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diff CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/share/man/man3/ev.3 @ 68:5028fdace37b
planemo upload commit 2e9511a184a1ca667c7be0c6321a36dc4e3d116d
| author | jpayne |
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| date | Tue, 18 Mar 2025 16:23:26 -0400 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/share/man/man3/ev.3 Tue Mar 18 16:23:26 2025 -0400 @@ -0,0 +1,5819 @@ +.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. 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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +libev \- a high performance full\-featured event loop written in C +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <ev.h> +.Ve +.SS "\s-1EXAMPLE PROGRAM\s0" +.IX Subsection "EXAMPLE PROGRAM" +.Vb 2 +\& // a single header file is required +\& #include <ev.h> +\& +\& #include <stdio.h> // for puts +\& +\& // every watcher type has its own typedef\*(Aqd struct +\& // with the name ev_TYPE +\& ev_io stdin_watcher; +\& ev_timer timeout_watcher; +\& +\& // all watcher callbacks have a similar signature +\& // this callback is called when data is readable on stdin +\& static void +\& stdin_cb (EV_P_ ev_io *w, int revents) +\& { +\& puts ("stdin ready"); +\& // for one\-shot events, one must manually stop the watcher +\& // with its corresponding stop function. +\& ev_io_stop (EV_A_ w); +\& +\& // this causes all nested ev_run\*(Aqs to stop iterating +\& ev_break (EV_A_ EVBREAK_ALL); +\& } +\& +\& // another callback, this time for a time\-out +\& static void +\& timeout_cb (EV_P_ ev_timer *w, int revents) +\& { +\& puts ("timeout"); +\& // this causes the innermost ev_run to stop iterating +\& ev_break (EV_A_ EVBREAK_ONE); +\& } +\& +\& int +\& main (void) +\& { +\& // use the default event loop unless you have special needs +\& struct ev_loop *loop = EV_DEFAULT; +\& +\& // initialise an io watcher, then start it +\& // this one will watch for stdin to become readable +\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); +\& ev_io_start (loop, &stdin_watcher); +\& +\& // initialise a timer watcher, then start it +\& // simple non\-repeating 5.5 second timeout +\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); +\& ev_timer_start (loop, &timeout_watcher); +\& +\& // now wait for events to arrive +\& ev_run (loop, 0); +\& +\& // break was called, so exit +\& return 0; +\& } +.Ve +.SH "ABOUT THIS DOCUMENT" +.IX Header "ABOUT THIS DOCUMENT" +This document documents the libev software package. +.PP +The newest version of this document is also available as an html-formatted +web page you might find easier to navigate when reading it for the first +time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. +.PP +While this document tries to be as complete as possible in documenting +libev, its usage and the rationale behind its design, it is not a tutorial +on event-based programming, nor will it introduce event-based programming +with libev. +.PP +Familiarity with event based programming techniques in general is assumed +throughout this document. +.SH "WHAT TO READ WHEN IN A HURRY" +.IX Header "WHAT TO READ WHEN IN A HURRY" +This manual tries to be very detailed, but unfortunately, this also makes +it very long. If you just want to know the basics of libev, I suggest +reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and +look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and +\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0. +.SH "ABOUT LIBEV" +.IX Header "ABOUT LIBEV" +Libev is an event loop: you register interest in certain events (such as a +file descriptor being readable or a timeout occurring), and it will manage +these event sources and provide your program with events. +.PP +To do this, it must take more or less complete control over your process +(or thread) by executing the \fIevent loop\fR handler, and will then +communicate events via a callback mechanism. +.PP +You register interest in certain events by registering so-called \fIevent +watchers\fR, which are relatively small C structures you initialise with the +details of the event, and then hand it over to libev by \fIstarting\fR the +watcher. +.SS "\s-1FEATURES\s0" +.IX Subsection "FEATURES" +Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR +interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port +mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR +interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner +inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative +timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling +(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status +change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event +loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and +\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even +limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR). +.PP +It also is quite fast (see this +benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent +for example). +.SS "\s-1CONVENTIONS\s0" +.IX Subsection "CONVENTIONS" +Libev is very configurable. In this manual the default (and most common) +configuration will be described, which supports multiple event loops. For +more info about various configuration options please have a look at +\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support +for multiple event loops, then all functions taking an initial argument of +name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have +this argument. +.SS "\s-1TIME REPRESENTATION\s0" +.IX Subsection "TIME REPRESENTATION" +Libev represents time as a single floating point number, representing +the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice +somewhere near the beginning of 1970, details are complicated, don't +ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use +too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do +any calculations on it, you should treat it as some floating point value. +.PP +Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for +time differences (e.g. delays) throughout libev. +.SH "ERROR HANDLING" +.IX Header "ERROR HANDLING" +Libev knows three classes of errors: operating system errors, usage errors +and internal errors (bugs). +.PP +When libev catches an operating system error it cannot handle (for example +a system call indicating a condition libev cannot fix), it calls the callback +set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or +abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort +()\*(C'\fR. +.PP +When libev detects a usage error such as a negative timer interval, then +it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism, +so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in +the libev caller and need to be fixed there. +.PP +Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR macro you can compile in and/or enable extensive +consistency checking code inside libev that can be used to check for +internal inconsistencies, suually caused by application bugs. +.PP +Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. These do not +trigger under normal circumstances, as they indicate either a bug in libev +or worse. +.SH "GLOBAL FUNCTIONS" +.IX Header "GLOBAL FUNCTIONS" +These functions can be called anytime, even before initialising the +library in any way. +.IP "ev_tstamp ev_time ()" 4 +.IX Item "ev_tstamp ev_time ()" +Returns the current time as libev would use it. Please note that the +\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp +you actually want to know. Also interesting is the combination of +\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR. +.IP "ev_sleep (ev_tstamp interval)" 4 +.IX Item "ev_sleep (ev_tstamp interval)" +Sleep for the given interval: The current thread will be blocked +until either it is interrupted or the given time interval has +passed (approximately \- it might return a bit earlier even if not +interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR. +.Sp +Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR. +.Sp +The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work +with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR). +.IP "int ev_version_major ()" 4 +.IX Item "int ev_version_major ()" +.PD 0 +.IP "int ev_version_minor ()" 4 +.IX Item "int ev_version_minor ()" +.PD +You can find out the major and minor \s-1ABI\s0 version numbers of the library +you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and +\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global +symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the +version of the library your program was compiled against. +.Sp +These version numbers refer to the \s-1ABI\s0 version of the library, not the +release version. +.Sp +Usually, it's a good idea to terminate if the major versions mismatch, +as this indicates an incompatible change. Minor versions are usually +compatible to older versions, so a larger minor version alone is usually +not a problem. +.Sp +Example: Make sure we haven't accidentally been linked against the wrong +version (note, however, that this will not detect other \s-1ABI\s0 mismatches, +such as \s-1LFS\s0 or reentrancy). +.Sp +.Vb 3 +\& assert (("libev version mismatch", +\& ev_version_major () == EV_VERSION_MAJOR +\& && ev_version_minor () >= EV_VERSION_MINOR)); +.Ve +.IP "unsigned int ev_supported_backends ()" 4 +.IX Item "unsigned int ev_supported_backends ()" +Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR +value) compiled into this binary of libev (independent of their +availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for +a description of the set values. +.Sp +Example: make sure we have the epoll method, because yeah this is cool and +a must have and can we have a torrent of it please!!!11 +.Sp +.Vb 2 +\& assert (("sorry, no epoll, no sex", +\& ev_supported_backends () & EVBACKEND_EPOLL)); +.Ve +.IP "unsigned int ev_recommended_backends ()" 4 +.IX Item "unsigned int ev_recommended_backends ()" +Return the set of all backends compiled into this binary of libev and +also recommended for this platform, meaning it will work for most file +descriptor types. This set is often smaller than the one returned by +\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs +and will not be auto-detected unless you explicitly request it (assuming +you know what you are doing). This is the set of backends that libev will +probe for if you specify no backends explicitly. +.IP "unsigned int ev_embeddable_backends ()" 4 +.IX Item "unsigned int ev_embeddable_backends ()" +Returns the set of backends that are embeddable in other event loops. This +value is platform-specific but can include backends not available on the +current system. To find which embeddable backends might be supported on +the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends () +& ev_supported_backends ()\*(C'\fR, likewise for recommended ones. +.Sp +See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. +.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4 +.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" +Sets the allocation function to use (the prototype is similar \- the +semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is +used to allocate and free memory (no surprises here). If it returns zero +when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort +or take some potentially destructive action. +.Sp +Since some systems (at least OpenBSD and Darwin) fail to implement +correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system +\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default. +.Sp +You could override this function in high-availability programs to, say, +free some memory if it cannot allocate memory, to use a special allocator, +or even to sleep a while and retry until some memory is available. +.Sp +Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses +which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and +is probably a good basis for your own implementation. +.Sp +.Vb 5 +\& static void * +\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT +\& { +\& if (size) +\& return realloc (ptr, size); +\& +\& free (ptr); +\& return 0; +\& } +.Ve +.Sp +Example: Replace the libev allocator with one that waits a bit and then +retries. +.Sp +.Vb 8 +\& static void * +\& persistent_realloc (void *ptr, size_t size) +\& { +\& if (!size) +\& { +\& free (ptr); +\& return 0; +\& } +\& +\& for (;;) +\& { +\& void *newptr = realloc (ptr, size); +\& +\& if (newptr) +\& return newptr; +\& +\& sleep (60); +\& } +\& } +\& +\& ... +\& ev_set_allocator (persistent_realloc); +.Ve +.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4 +.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" +Set the callback function to call on a retryable system call error (such +as failed select, poll, epoll_wait). The message is a printable string +indicating the system call or subsystem causing the problem. If this +callback is set, then libev will expect it to remedy the situation, no +matter what, when it returns. That is, libev will generally retry the +requested operation, or, if the condition doesn't go away, do bad stuff +(such as abort). +.Sp +Example: This is basically the same thing that libev does internally, too. +.Sp +.Vb 6 +\& static void +\& fatal_error (const char *msg) +\& { +\& perror (msg); +\& abort (); +\& } +\& +\& ... +\& ev_set_syserr_cb (fatal_error); +.Ve +.IP "ev_feed_signal (int signum)" 4 +.IX Item "ev_feed_signal (int signum)" +This function can be used to \*(L"simulate\*(R" a signal receive. It is completely +safe to call this function at any time, from any context, including signal +handlers or random threads. +.Sp +Its main use is to customise signal handling in your process, especially +in the presence of threads. For example, you could block signals +by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when +creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other +mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling +\&\f(CW\*(C`ev_feed_signal\*(C'\fR. +.SH "FUNCTIONS CONTROLLING EVENT LOOPS" +.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS" +An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is +\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as +libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name). +.PP +The library knows two types of such loops, the \fIdefault\fR loop, which +supports child process events, and dynamically created event loops which +do not. +.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 +.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" +This returns the \*(L"default\*(R" event loop object, which is what you should +normally use when you just need \*(L"the event loop\*(R". Event loop objects and +the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for +\&\f(CW\*(C`ev_loop_new\*(C'\fR. +.Sp +If the default loop is already initialised then this function simply +returns it (and ignores the flags. If that is troubling you, check +\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given +flags, which should almost always be \f(CW0\fR, unless the caller is also the +one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R". +.Sp +If you don't know what event loop to use, use the one returned from this +function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro). +.Sp +Note that this function is \fInot\fR thread-safe, so if you want to use it +from multiple threads, you have to employ some kind of mutex (note also +that this case is unlikely, as loops cannot be shared easily between +threads anyway). +.Sp +The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers, +and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is +a problem for your application you can either create a dynamic loop with +\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the +\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR. +.Sp +Example: This is the most typical usage. +.Sp +.Vb 2 +\& if (!ev_default_loop (0)) +\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); +.Ve +.Sp +Example: Restrict libev to the select and poll backends, and do not allow +environment settings to be taken into account: +.Sp +.Vb 1 +\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); +.Ve +.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 +.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" +This will create and initialise a new event loop object. If the loop +could not be initialised, returns false. +.Sp +This function is thread-safe, and one common way to use libev with +threads is indeed to create one loop per thread, and using the default +loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread. +.Sp +The flags argument can be used to specify special behaviour or specific +backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). +.Sp +The following flags are supported: +.RS 4 +.ie n .IP """EVFLAG_AUTO""" 4 +.el .IP "\f(CWEVFLAG_AUTO\fR" 4 +.IX Item "EVFLAG_AUTO" +The default flags value. Use this if you have no clue (it's the right +thing, believe me). +.ie n .IP """EVFLAG_NOENV""" 4 +.el .IP "\f(CWEVFLAG_NOENV\fR" 4 +.IX Item "EVFLAG_NOENV" +If this flag bit is or'ed into the flag value (or the program runs setuid +or setgid) then libev will \fInot\fR look at the environment variable +\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will +override the flags completely if it is found in the environment. This is +useful to try out specific backends to test their performance, to work +around bugs, or to make libev threadsafe (accessing environment variables +cannot be done in a threadsafe way, but usually it works if no other +thread modifies them). +.ie n .IP """EVFLAG_FORKCHECK""" 4 +.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 +.IX Item "EVFLAG_FORKCHECK" +Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also +make libev check for a fork in each iteration by enabling this flag. +.Sp +This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, +and thus this might slow down your event loop if you do a lot of loop +iterations and little real work, but is usually not noticeable (on my +GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn +sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux +system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc +versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again). +.Sp +The big advantage of this flag is that you can forget about fork (and +forget about forgetting to tell libev about forking, although you still +have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag. +.Sp +This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR +environment variable. +.ie n .IP """EVFLAG_NOINOTIFY""" 4 +.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4 +.IX Item "EVFLAG_NOINOTIFY" +When this flag is specified, then libev will not attempt to use the +\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and +testing, this flag can be useful to conserve inotify file descriptors, as +otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle. +.ie n .IP """EVFLAG_SIGNALFD""" 4 +.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4 +.IX Item "EVFLAG_SIGNALFD" +When this flag is specified, then libev will attempt to use the +\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0 +delivers signals synchronously, which makes it both faster and might make +it possible to get the queued signal data. It can also simplify signal +handling with threads, as long as you properly block signals in your +threads that are not interested in handling them. +.Sp +Signalfd will not be used by default as this changes your signal mask, and +there are a lot of shoddy libraries and programs (glib's threadpool for +example) that can't properly initialise their signal masks. +.ie n .IP """EVFLAG_NOSIGMASK""" 4 +.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4 +.IX Item "EVFLAG_NOSIGMASK" +When this flag is specified, then libev will avoid to modify the signal +mask. Specifically, this means you have to make sure signals are unblocked +when you want to receive them. +.Sp +This behaviour is useful when you want to do your own signal handling, or +want to handle signals only in specific threads and want to avoid libev +unblocking the signals. +.Sp +It's also required by \s-1POSIX\s0 in a threaded program, as libev calls +\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified. +.ie n .IP """EVFLAG_NOTIMERFD""" 4 +.el .IP "\f(CWEVFLAG_NOTIMERFD\fR" 4 +.IX Item "EVFLAG_NOTIMERFD" +When this flag is specified, the libev will avoid using a \f(CW\*(C`timerfd\*(C'\fR to +detect time jumps. It will still be able to detect time jumps, but takes +longer and has a lower accuracy in doing so, but saves a file descriptor +per loop. +.Sp +The current implementation only tries to use a \f(CW\*(C`timerfd\*(C'\fR when the first +\&\f(CW\*(C`ev_periodic\*(C'\fR watcher is started and falls back on other methods if it +cannot be created, but this behaviour might change in the future. +.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 +.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 +.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" +This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as +libev tries to roll its own fd_set with no limits on the number of fds, +but if that fails, expect a fairly low limit on the number of fds when +using this backend. It doesn't scale too well (O(highest_fd)), but its +usually the fastest backend for a low number of (low-numbered :) fds. +.Sp +To get good performance out of this backend you need a high amount of +parallelism (most of the file descriptors should be busy). If you are +writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many +connections as possible during one iteration. You might also want to have +a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of +readiness notifications you get per iteration. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the +\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the +\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform). +.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 +.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 +.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" +And this is your standard \fBpoll\fR\|(2) backend. It's more complicated +than select, but handles sparse fds better and has no artificial +limit on the number of fds you can use (except it will slow down +considerably with a lot of inactive fds). It scales similarly to select, +i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for +performance tips. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and +\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR. +.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 +.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 +.IX Item "EVBACKEND_EPOLL (value 4, Linux)" +Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9 +kernels). +.Sp +For few fds, this backend is a bit little slower than poll and select, but +it scales phenomenally better. While poll and select usually scale like +O(total_fds) where total_fds is the total number of fds (or the highest +fd), epoll scales either O(1) or O(active_fds). +.Sp +The epoll mechanism deserves honorable mention as the most misdesigned +of the more advanced event mechanisms: mere annoyances include silently +dropping file descriptors, requiring a system call per change per file +descriptor (and unnecessary guessing of parameters), problems with dup, +returning before the timeout value, resulting in additional iterations +(and only giving 5ms accuracy while select on the same platform gives +0.1ms) and so on. The biggest issue is fork races, however \- if a program +forks then \fIboth\fR parent and child process have to recreate the epoll +set, which can take considerable time (one syscall per file descriptor) +and is of course hard to detect. +.Sp +Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, +but of course \fIdoesn't\fR, and epoll just loves to report events for +totally \fIdifferent\fR file descriptors (even already closed ones, so +one cannot even remove them from the set) than registered in the set +(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious +notifications by employing an additional generation counter and comparing +that against the events to filter out spurious ones, recreating the set +when required. Epoll also erroneously rounds down timeouts, but gives you +no way to know when and by how much, so sometimes you have to busy-wait +because epoll returns immediately despite a nonzero timeout. And last +not least, it also refuses to work with some file descriptors which work +perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...). +.Sp +Epoll is truly the train wreck among event poll mechanisms, a frankenpoll, +cobbled together in a hurry, no thought to design or interaction with +others. Oh, the pain, will it ever stop... +.Sp +While stopping, setting and starting an I/O watcher in the same iteration +will result in some caching, there is still a system call per such +incident (because the same \fIfile descriptor\fR could point to a different +\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed +file descriptors might not work very well if you register events for both +file descriptors. +.Sp +Best performance from this backend is achieved by not unregistering all +watchers for a file descriptor until it has been closed, if possible, +i.e. keep at least one watcher active per fd at all times. Stopping and +starting a watcher (without re-setting it) also usually doesn't cause +extra overhead. A fork can both result in spurious notifications as well +as in libev having to destroy and recreate the epoll object, which can +take considerable time and thus should be avoided. +.Sp +All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or +faster than epoll for maybe up to a hundred file descriptors, depending on +the usage. So sad. +.Sp +While nominally embeddable in other event loops, this feature is broken in +a lot of kernel revisions, but probably(!) works in current versions. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as +\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4 +.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4 +.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)" +Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev +only tries to use it in 4.19+). +.Sp +This is another Linux train wreck of an event interface. +.Sp +If this backend works for you (as of this writing, it was very +experimental), it is the best event interface available on Linux and might +be well worth enabling it \- if it isn't available in your kernel this will +be detected and this backend will be skipped. +.Sp +This backend can batch oneshot requests and supports a user-space ring +buffer to receive events. It also doesn't suffer from most of the design +problems of epoll (such as not being able to remove event sources from +the epoll set), and generally sounds too good to be true. Because, this +being the Linux kernel, of course it suffers from a whole new set of +limitations, forcing you to fall back to epoll, inheriting all its design +issues. +.Sp +For one, it is not easily embeddable (but probably could be done using +an event fd at some extra overhead). It also is subject to a system wide +limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0 +requests are left, this backend will be skipped during initialisation, and +will switch to epoll when the loop is active. +.Sp +Most problematic in practice, however, is that not all file descriptors +work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds, +files, \fI/dev/null\fR and many others are supported, but ttys do not work +properly (a known bug that the kernel developers don't care about, see +<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not +(yet?) a generic event polling interface. +.Sp +Overall, it seems the Linux developers just don't want it to have a +generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR. +.Sp +To work around all these problem, the current version of libev uses its +epoll backend as a fallback for file descriptor types that do not work. Or +falls back completely to epoll if the kernel acts up. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as +\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 +.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 +.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" +Kqueue deserves special mention, as at the time this backend was +implemented, it was broken on all BSDs except NetBSD (usually it doesn't +work reliably with anything but sockets and pipes, except on Darwin, +where of course it's completely useless). Unlike epoll, however, whose +brokenness is by design, these kqueue bugs can be (and mostly have been) +fixed without \s-1API\s0 changes to existing programs. For this reason it's not +being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it +in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a +known-to-be-good (\-enough) system like NetBSD. +.Sp +You still can embed kqueue into a normal poll or select backend and use it +only for sockets (after having made sure that sockets work with kqueue on +the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. +.Sp +It scales in the same way as the epoll backend, but the interface to the +kernel is more efficient (which says nothing about its actual speed, of +course). While stopping, setting and starting an I/O watcher does never +cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to +two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you +might have to leak fds on fork, but it's more sane than epoll) and it +drops fds silently in similarly hard-to-detect cases. +.Sp +This backend usually performs well under most conditions. +.Sp +While nominally embeddable in other event loops, this doesn't work +everywhere, so you might need to test for this. And since it is broken +almost everywhere, you should only use it when you have a lot of sockets +(for which it usually works), by embedding it into another event loop +(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course +also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with +\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with +\&\f(CW\*(C`NOTE_EOF\*(C'\fR. +.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 +.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 +.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" +This is not implemented yet (and might never be, unless you send me an +implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets +and is not embeddable, which would limit the usefulness of this backend +immensely. +.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 +.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 +.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" +This uses the Solaris 10 event port mechanism. As with everything on Solaris, +it's really slow, but it still scales very well (O(active_fds)). +.Sp +While this backend scales well, it requires one system call per active +file descriptor per loop iteration. For small and medium numbers of file +descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend +might perform better. +.Sp +On the positive side, this backend actually performed fully to +specification in all tests and is fully embeddable, which is a rare feat +among the OS-specific backends (I vastly prefer correctness over speed +hacks). +.Sp +On the negative side, the interface is \fIbizarre\fR \- so bizarre that +even sun itself gets it wrong in their code examples: The event polling +function sometimes returns events to the caller even though an error +occurred, but with no indication whether it has done so or not (yes, it's +even documented that way) \- deadly for edge-triggered interfaces where you +absolutely have to know whether an event occurred or not because you have +to re-arm the watcher. +.Sp +Fortunately libev seems to be able to work around these idiocies. +.Sp +This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as +\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.ie n .IP """EVBACKEND_ALL""" 4 +.el .IP "\f(CWEVBACKEND_ALL\fR" 4 +.IX Item "EVBACKEND_ALL" +Try all backends (even potentially broken ones that wouldn't be tried +with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as +\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. +.Sp +It is definitely not recommended to use this flag, use whatever +\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend +at all. +.ie n .IP """EVBACKEND_MASK""" 4 +.el .IP "\f(CWEVBACKEND_MASK\fR" 4 +.IX Item "EVBACKEND_MASK" +Not a backend at all, but a mask to select all backend bits from a +\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags +value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable). +.RE +.RS 4 +.Sp +If one or more of the backend flags are or'ed into the flags value, +then only these backends will be tried (in the reverse order as listed +here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends +()\*(C'\fR will be tried. +.Sp +Example: Try to create a event loop that uses epoll and nothing else. +.Sp +.Vb 3 +\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); +\& if (!epoller) +\& fatal ("no epoll found here, maybe it hides under your chair"); +.Ve +.Sp +Example: Use whatever libev has to offer, but make sure that kqueue is +used if available. +.Sp +.Vb 1 +\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE); +.Ve +.Sp +Example: Similarly, on linux, you mgiht want to take advantage of the +linux aio backend if possible, but fall back to something else if that +isn't available. +.Sp +.Vb 1 +\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO); +.Ve +.RE +.IP "ev_loop_destroy (loop)" 4 +.IX Item "ev_loop_destroy (loop)" +Destroys an event loop object (frees all memory and kernel state +etc.). None of the active event watchers will be stopped in the normal +sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your +responsibility to either stop all watchers cleanly yourself \fIbefore\fR +calling this function, or cope with the fact afterwards (which is usually +the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them +for example). +.Sp +Note that certain global state, such as signal state (and installed signal +handlers), will not be freed by this function, and related watchers (such +as signal and child watchers) would need to be stopped manually. +.Sp +This function is normally used on loop objects allocated by +\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by +\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe. +.Sp +Note that it is not advisable to call this function on the default loop +except in the rare occasion where you really need to free its resources. +If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR +and \f(CW\*(C`ev_loop_destroy\*(C'\fR. +.IP "ev_loop_fork (loop)" 4 +.IX Item "ev_loop_fork (loop)" +This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations +to reinitialise the kernel state for backends that have one. Despite +the name, you can call it anytime you are allowed to start or stop +watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most +sense after forking, in the child process. You \fImust\fR call it (or use +\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR. +.Sp +In addition, if you want to reuse a loop (via this function or +\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR. +.Sp +Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after +a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is +because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things +during fork. +.Sp +On the other hand, you only need to call this function in the child +process if and only if you want to use the event loop in the child. If +you just fork+exec or create a new loop in the child, you don't have to +call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a +difference, but libev will usually detect this case on its own and do a +costly reset of the backend). +.Sp +The function itself is quite fast and it's usually not a problem to call +it just in case after a fork. +.Sp +Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when +using pthreads. +.Sp +.Vb 5 +\& static void +\& post_fork_child (void) +\& { +\& ev_loop_fork (EV_DEFAULT); +\& } +\& +\& ... +\& pthread_atfork (0, 0, post_fork_child); +.Ve +.IP "int ev_is_default_loop (loop)" 4 +.IX Item "int ev_is_default_loop (loop)" +Returns true when the given loop is, in fact, the default loop, and false +otherwise. +.IP "unsigned int ev_iteration (loop)" 4 +.IX Item "unsigned int ev_iteration (loop)" +Returns the current iteration count for the event loop, which is identical +to the number of times libev did poll for new events. It starts at \f(CW0\fR +and happily wraps around with enough iterations. +.Sp +This value can sometimes be useful as a generation counter of sorts (it +\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with +\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the +prepare and check phases. +.IP "unsigned int ev_depth (loop)" 4 +.IX Item "unsigned int ev_depth (loop)" +Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of +times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth. +.Sp +Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is +\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread), +in which case it is higher. +.Sp +Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread, +throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this +as a hint to avoid such ungentleman-like behaviour unless it's really +convenient, in which case it is fully supported. +.IP "unsigned int ev_backend (loop)" 4 +.IX Item "unsigned int ev_backend (loop)" +Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in +use. +.IP "ev_tstamp ev_now (loop)" 4 +.IX Item "ev_tstamp ev_now (loop)" +Returns the current \*(L"event loop time\*(R", which is the time the event loop +received events and started processing them. This timestamp does not +change as long as callbacks are being processed, and this is also the base +time used for relative timers. You can treat it as the timestamp of the +event occurring (or more correctly, libev finding out about it). +.IP "ev_now_update (loop)" 4 +.IX Item "ev_now_update (loop)" +Establishes the current time by querying the kernel, updating the time +returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and +is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR. +.Sp +This function is rarely useful, but when some event callback runs for a +very long time without entering the event loop, updating libev's idea of +the current time is a good idea. +.Sp +See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section. +.IP "ev_suspend (loop)" 4 +.IX Item "ev_suspend (loop)" +.PD 0 +.IP "ev_resume (loop)" 4 +.IX Item "ev_resume (loop)" +.PD +These two functions suspend and resume an event loop, for use when the +loop is not used for a while and timeouts should not be processed. +.Sp +A typical use case would be an interactive program such as a game: When +the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it +would be best to handle timeouts as if no time had actually passed while +the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR +in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling +\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing. +.Sp +Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend +between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers +will be rescheduled (that is, they will lose any events that would have +occurred while suspended). +.Sp +After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the +given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR +without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR. +.Sp +Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the +event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR). +.IP "bool ev_run (loop, int flags)" 4 +.IX Item "bool ev_run (loop, int flags)" +Finally, this is it, the event handler. This function usually is called +after you have initialised all your watchers and you want to start +handling events. It will ask the operating system for any new events, call +the watcher callbacks, and then repeat the whole process indefinitely: This +is why event loops are called \fIloops\fR. +.Sp +If the flags argument is specified as \f(CW0\fR, it will keep handling events +until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was +called. +.Sp +The return value is false if there are no more active watchers (which +usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases +(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again"). +.Sp +Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than +relying on all watchers to be stopped when deciding when a program has +finished (especially in interactive programs), but having a program +that automatically loops as long as it has to and no longer by virtue +of relying on its watchers stopping correctly, that is truly a thing of +beauty. +.Sp +This function is \fImostly\fR exception-safe \- you can break out of a +\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+ +exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor +will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks. +.Sp +A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle +those events and any already outstanding ones, but will not wait and +block your process in case there are no events and will return after one +iteration of the loop. This is sometimes useful to poll and handle new +events while doing lengthy calculations, to keep the program responsive. +.Sp +A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if +necessary) and will handle those and any already outstanding ones. It +will block your process until at least one new event arrives (which could +be an event internal to libev itself, so there is no guarantee that a +user-registered callback will be called), and will return after one +iteration of the loop. +.Sp +This is useful if you are waiting for some external event in conjunction +with something not expressible using other libev watchers (i.e. "roll your +own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is +usually a better approach for this kind of thing. +.Sp +Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your +understanding, not a guarantee that things will work exactly like this in +future versions): +.Sp +.Vb 10 +\& \- Increment loop depth. +\& \- Reset the ev_break status. +\& \- Before the first iteration, call any pending watchers. +\& LOOP: +\& \- If EVFLAG_FORKCHECK was used, check for a fork. +\& \- If a fork was detected (by any means), queue and call all fork watchers. +\& \- Queue and call all prepare watchers. +\& \- If ev_break was called, goto FINISH. +\& \- If we have been forked, detach and recreate the kernel state +\& as to not disturb the other process. +\& \- Update the kernel state with all outstanding changes. +\& \- Update the "event loop time" (ev_now ()). +\& \- Calculate for how long to sleep or block, if at all +\& (active idle watchers, EVRUN_NOWAIT or not having +\& any active watchers at all will result in not sleeping). +\& \- Sleep if the I/O and timer collect interval say so. +\& \- Increment loop iteration counter. +\& \- Block the process, waiting for any events. +\& \- Queue all outstanding I/O (fd) events. +\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments. +\& \- Queue all expired timers. +\& \- Queue all expired periodics. +\& \- Queue all idle watchers with priority higher than that of pending events. +\& \- Queue all check watchers. +\& \- Call all queued watchers in reverse order (i.e. check watchers first). +\& Signals and child watchers are implemented as I/O watchers, and will +\& be handled here by queueing them when their watcher gets executed. +\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT +\& were used, or there are no active watchers, goto FINISH, otherwise +\& continue with step LOOP. +\& FINISH: +\& \- Reset the ev_break status iff it was EVBREAK_ONE. +\& \- Decrement the loop depth. +\& \- Return. +.Ve +.Sp +Example: Queue some jobs and then loop until no events are outstanding +anymore. +.Sp +.Vb 4 +\& ... queue jobs here, make sure they register event watchers as long +\& ... as they still have work to do (even an idle watcher will do..) +\& ev_run (my_loop, 0); +\& ... jobs done or somebody called break. yeah! +.Ve +.IP "ev_break (loop, how)" 4 +.IX Item "ev_break (loop, how)" +Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it +has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either +\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or +\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return. +.Sp +This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR. +.Sp +It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in +which case it will have no effect. +.IP "ev_ref (loop)" 4 +.IX Item "ev_ref (loop)" +.PD 0 +.IP "ev_unref (loop)" 4 +.IX Item "ev_unref (loop)" +.PD +Ref/unref can be used to add or remove a reference count on the event +loop: Every watcher keeps one reference, and as long as the reference +count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own. +.Sp +This is useful when you have a watcher that you never intend to +unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from +returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR +before stopping it. +.Sp +As an example, libev itself uses this for its internal signal pipe: It +is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from +exiting if no event watchers registered by it are active. It is also an +excellent way to do this for generic recurring timers or from within +third-party libraries. Just remember to \fIunref after start\fR and \fIref +before stop\fR (but only if the watcher wasn't active before, or was active +before, respectively. Note also that libev might stop watchers itself +(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR +in the callback). +.Sp +Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR +running when nothing else is active. +.Sp +.Vb 4 +\& ev_signal exitsig; +\& ev_signal_init (&exitsig, sig_cb, SIGINT); +\& ev_signal_start (loop, &exitsig); +\& ev_unref (loop); +.Ve +.Sp +Example: For some weird reason, unregister the above signal handler again. +.Sp +.Vb 2 +\& ev_ref (loop); +\& ev_signal_stop (loop, &exitsig); +.Ve +.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4 +.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)" +.PD 0 +.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4 +.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" +.PD +These advanced functions influence the time that libev will spend waiting +for events. Both time intervals are by default \f(CW0\fR, meaning that libev +will try to invoke timer/periodic callbacks and I/O callbacks with minimum +latency. +.Sp +Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR) +allows libev to delay invocation of I/O and timer/periodic callbacks +to increase efficiency of loop iterations (or to increase power-saving +opportunities). +.Sp +The idea is that sometimes your program runs just fast enough to handle +one (or very few) event(s) per loop iteration. While this makes the +program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new +events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high +overhead for the actual polling but can deliver many events at once. +.Sp +By setting a higher \fIio collect interval\fR you allow libev to spend more +time collecting I/O events, so you can handle more events per iteration, +at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and +\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will +introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The +sleep time ensures that libev will not poll for I/O events more often then +once per this interval, on average (as long as the host time resolution is +good enough). +.Sp +Likewise, by setting a higher \fItimeout collect interval\fR you allow libev +to spend more time collecting timeouts, at the expense of increased +latency/jitter/inexactness (the watcher callback will be called +later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null +value will not introduce any overhead in libev. +.Sp +Many (busy) programs can usually benefit by setting the I/O collect +interval to a value near \f(CW0.1\fR or so, which is often enough for +interactive servers (of course not for games), likewise for timeouts. It +usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR, +as this approaches the timing granularity of most systems. Note that if +you do transactions with the outside world and you can't increase the +parallelity, then this setting will limit your transaction rate (if you +need to poll once per transaction and the I/O collect interval is 0.01, +then you can't do more than 100 transactions per second). +.Sp +Setting the \fItimeout collect interval\fR can improve the opportunity for +saving power, as the program will \*(L"bundle\*(R" timer callback invocations that +are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of +times the process sleeps and wakes up again. Another useful technique to +reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure +they fire on, say, one-second boundaries only. +.Sp +Example: we only need 0.1s timeout granularity, and we wish not to poll +more often than 100 times per second: +.Sp +.Vb 2 +\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1); +\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01); +.Ve +.IP "ev_invoke_pending (loop)" 4 +.IX Item "ev_invoke_pending (loop)" +This call will simply invoke all pending watchers while resetting their +pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required, +but when overriding the invoke callback this call comes handy. This +function can be invoked from a watcher \- this can be useful for example +when you want to do some lengthy calculation and want to pass further +event handling to another thread (you still have to make sure only one +thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course). +.IP "int ev_pending_count (loop)" 4 +.IX Item "int ev_pending_count (loop)" +Returns the number of pending watchers \- zero indicates that no watchers +are pending. +.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4 +.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))" +This overrides the invoke pending functionality of the loop: Instead of +invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call +this callback instead. This is useful, for example, when you want to +invoke the actual watchers inside another context (another thread etc.). +.Sp +If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new +callback. +.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4 +.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())" +Sometimes you want to share the same loop between multiple threads. This +can be done relatively simply by putting mutex_lock/unlock calls around +each call to a libev function. +.Sp +However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible +to wait for it to return. One way around this is to wake up the event +loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these +\&\fIrelease\fR and \fIacquire\fR callbacks on the loop. +.Sp +When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is +suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just +afterwards. +.Sp +Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and +\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again. +.Sp +While event loop modifications are allowed between invocations of +\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no +modifications done will affect the event loop, i.e. adding watchers will +have no effect on the set of file descriptors being watched, or the time +waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it +to take note of any changes you made. +.Sp +In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between +invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR. +.Sp +See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this +document. +.IP "ev_set_userdata (loop, void *data)" 4 +.IX Item "ev_set_userdata (loop, void *data)" +.PD 0 +.IP "void *ev_userdata (loop)" 4 +.IX Item "void *ev_userdata (loop)" +.PD +Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When +\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns +\&\f(CW0\fR. +.Sp +These two functions can be used to associate arbitrary data with a loop, +and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and +\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for +any other purpose as well. +.IP "ev_verify (loop)" 4 +.IX Item "ev_verify (loop)" +This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been +compiled in, which is the default for non-minimal builds. It tries to go +through all internal structures and checks them for validity. If anything +is found to be inconsistent, it will print an error message to standard +error and call \f(CW\*(C`abort ()\*(C'\fR. +.Sp +This can be used to catch bugs inside libev itself: under normal +circumstances, this function will never abort as of course libev keeps its +data structures consistent. +.SH "ANATOMY OF A WATCHER" +.IX Header "ANATOMY OF A WATCHER" +In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the +watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer +watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers. +.PP +A watcher is an opaque structure that you allocate and register to record +your interest in some event. To make a concrete example, imagine you want +to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher +for that: +.PP +.Vb 5 +\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents) +\& { +\& ev_io_stop (w); +\& ev_break (loop, EVBREAK_ALL); +\& } +\& +\& struct ev_loop *loop = ev_default_loop (0); +\& +\& ev_io stdin_watcher; +\& +\& ev_init (&stdin_watcher, my_cb); +\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); +\& ev_io_start (loop, &stdin_watcher); +\& +\& ev_run (loop, 0); +.Ve +.PP +As you can see, you are responsible for allocating the memory for your +watcher structures (and it is \fIusually\fR a bad idea to do this on the +stack). +.PP +Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR +or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs). +.PP +Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher +*, callback)\*(C'\fR, which expects a callback to be provided. This callback is +invoked each time the event occurs (or, in the case of I/O watchers, each +time the event loop detects that the file descriptor given is readable +and/or writable). +.PP +Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR +macro to configure it, with arguments specific to the watcher type. There +is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR. +.PP +To make the watcher actually watch out for events, you have to start it +with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher +*)\*(C'\fR), and you can stop watching for events at any time by calling the +corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR. +.PP +As long as your watcher is active (has been started but not stopped) you +must not touch the values stored in it except when explicitly documented +otherwise. Most specifically you must never reinitialise it or call its +\&\f(CW\*(C`ev_TYPE_set\*(C'\fR macro. +.PP +Each and every callback receives the event loop pointer as first, the +registered watcher structure as second, and a bitset of received events as +third argument. +.PP +The received events usually include a single bit per event type received +(you can receive multiple events at the same time). The possible bit masks +are: +.ie n .IP """EV_READ""" 4 +.el .IP "\f(CWEV_READ\fR" 4 +.IX Item "EV_READ" +.PD 0 +.ie n .IP """EV_WRITE""" 4 +.el .IP "\f(CWEV_WRITE\fR" 4 +.IX Item "EV_WRITE" +.PD +The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or +writable. +.ie n .IP """EV_TIMER""" 4 +.el .IP "\f(CWEV_TIMER\fR" 4 +.IX Item "EV_TIMER" +The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. +.ie n .IP """EV_PERIODIC""" 4 +.el .IP "\f(CWEV_PERIODIC\fR" 4 +.IX Item "EV_PERIODIC" +The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. +.ie n .IP """EV_SIGNAL""" 4 +.el .IP "\f(CWEV_SIGNAL\fR" 4 +.IX Item "EV_SIGNAL" +The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. +.ie n .IP """EV_CHILD""" 4 +.el .IP "\f(CWEV_CHILD\fR" 4 +.IX Item "EV_CHILD" +The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. +.ie n .IP """EV_STAT""" 4 +.el .IP "\f(CWEV_STAT\fR" 4 +.IX Item "EV_STAT" +The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow. +.ie n .IP """EV_IDLE""" 4 +.el .IP "\f(CWEV_IDLE\fR" 4 +.IX Item "EV_IDLE" +The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. +.ie n .IP """EV_PREPARE""" 4 +.el .IP "\f(CWEV_PREPARE\fR" 4 +.IX Item "EV_PREPARE" +.PD 0 +.ie n .IP """EV_CHECK""" 4 +.el .IP "\f(CWEV_CHECK\fR" 4 +.IX Item "EV_CHECK" +.PD +All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to +gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked) +just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks +for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last +watchers invoked before the event loop sleeps or polls for new events, and +\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same +or lower priority within an event loop iteration. +.Sp +Callbacks of both watcher types can start and stop as many watchers as +they want, and all of them will be taken into account (for example, a +\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from +blocking). +.ie n .IP """EV_EMBED""" 4 +.el .IP "\f(CWEV_EMBED\fR" 4 +.IX Item "EV_EMBED" +The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. +.ie n .IP """EV_FORK""" 4 +.el .IP "\f(CWEV_FORK\fR" 4 +.IX Item "EV_FORK" +The event loop has been resumed in the child process after fork (see +\&\f(CW\*(C`ev_fork\*(C'\fR). +.ie n .IP """EV_CLEANUP""" 4 +.el .IP "\f(CWEV_CLEANUP\fR" 4 +.IX Item "EV_CLEANUP" +The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR). +.ie n .IP """EV_ASYNC""" 4 +.el .IP "\f(CWEV_ASYNC\fR" 4 +.IX Item "EV_ASYNC" +The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR). +.ie n .IP """EV_CUSTOM""" 4 +.el .IP "\f(CWEV_CUSTOM\fR" 4 +.IX Item "EV_CUSTOM" +Not ever sent (or otherwise used) by libev itself, but can be freely used +by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR). +.ie n .IP """EV_ERROR""" 4 +.el .IP "\f(CWEV_ERROR\fR" 4 +.IX Item "EV_ERROR" +An unspecified error has occurred, the watcher has been stopped. This might +happen because the watcher could not be properly started because libev +ran out of memory, a file descriptor was found to be closed or any other +problem. Libev considers these application bugs. +.Sp +You best act on it by reporting the problem and somehow coping with the +watcher being stopped. Note that well-written programs should not receive +an error ever, so when your watcher receives it, this usually indicates a +bug in your program. +.Sp +Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for +example it might indicate that a fd is readable or writable, and if your +callbacks is well-written it can just attempt the operation and cope with +the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded +programs, though, as the fd could already be closed and reused for another +thing, so beware. +.SS "\s-1GENERIC WATCHER FUNCTIONS\s0" +.IX Subsection "GENERIC WATCHER FUNCTIONS" +.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 +.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 +.IX Item "ev_init (ev_TYPE *watcher, callback)" +This macro initialises the generic portion of a watcher. The contents +of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only +the generic parts of the watcher are initialised, you \fIneed\fR to call +the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the +type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro +which rolls both calls into one. +.Sp +You can reinitialise a watcher at any time as long as it has been stopped +(or never started) and there are no pending events outstanding. +.Sp +The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher, +int revents)\*(C'\fR. +.Sp +Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps. +.Sp +.Vb 3 +\& ev_io w; +\& ev_init (&w, my_cb); +\& ev_io_set (&w, STDIN_FILENO, EV_READ); +.Ve +.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4 +.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4 +.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])" +This macro initialises the type-specific parts of a watcher. You need to +call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can +call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this +macro on a watcher that is active (it can be pending, however, which is a +difference to the \f(CW\*(C`ev_init\*(C'\fR macro). +.Sp +Although some watcher types do not have type-specific arguments +(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. +.Sp +See \f(CW\*(C`ev_init\*(C'\fR, above, for an example. +.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 +.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 +.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" +This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro +calls into a single call. This is the most convenient method to initialise +a watcher. The same limitations apply, of course. +.Sp +Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step. +.Sp +.Vb 1 +\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ); +.Ve +.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4 +.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4 +.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)" +Starts (activates) the given watcher. Only active watchers will receive +events. If the watcher is already active nothing will happen. +.Sp +Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this +whole section. +.Sp +.Vb 1 +\& ev_io_start (EV_DEFAULT_UC, &w); +.Ve +.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4 +.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4 +.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)" +Stops the given watcher if active, and clears the pending status (whether +the watcher was active or not). +.Sp +It is possible that stopped watchers are pending \- for example, +non-repeating timers are being stopped when they become pending \- but +calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor +pending. If you want to free or reuse the memory used by the watcher it is +therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. +.IP "bool ev_is_active (ev_TYPE *watcher)" 4 +.IX Item "bool ev_is_active (ev_TYPE *watcher)" +Returns a true value iff the watcher is active (i.e. it has been started +and not yet been stopped). As long as a watcher is active you must not modify +it. +.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 +.IX Item "bool ev_is_pending (ev_TYPE *watcher)" +Returns a true value iff the watcher is pending, (i.e. it has outstanding +events but its callback has not yet been invoked). As long as a watcher +is pending (but not active) you must not call an init function on it (but +\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must +make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR +it). +.IP "callback ev_cb (ev_TYPE *watcher)" 4 +.IX Item "callback ev_cb (ev_TYPE *watcher)" +Returns the callback currently set on the watcher. +.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4 +.IX Item "ev_set_cb (ev_TYPE *watcher, callback)" +Change the callback. You can change the callback at virtually any time +(modulo threads). +.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4 +.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)" +.PD 0 +.IP "int ev_priority (ev_TYPE *watcher)" 4 +.IX Item "int ev_priority (ev_TYPE *watcher)" +.PD +Set and query the priority of the watcher. The priority is a small +integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR +(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked +before watchers with lower priority, but priority will not keep watchers +from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). +.Sp +If you need to suppress invocation when higher priority events are pending +you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. +.Sp +You \fImust not\fR change the priority of a watcher as long as it is active or +pending. +.Sp +Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is +fine, as long as you do not mind that the priority value you query might +or might not have been clamped to the valid range. +.Sp +The default priority used by watchers when no priority has been set is +always \f(CW0\fR, which is supposed to not be too high and not be too low :). +.Sp +See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of +priorities. +.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 +.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" +Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither +\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback +can deal with that fact, as both are simply passed through to the +callback. +.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 +.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" +If the watcher is pending, this function clears its pending status and +returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the +watcher isn't pending it does nothing and returns \f(CW0\fR. +.Sp +Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its +callback to be invoked, which can be accomplished with this function. +.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4 +.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)" +Feeds the given event set into the event loop, as if the specified event +had happened for the specified watcher (which must be a pointer to an +initialised but not necessarily started event watcher). Obviously you must +not free the watcher as long as it has pending events. +.Sp +Stopping the watcher, letting libev invoke it, or calling +\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was +not started in the first place. +.Sp +See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related +functions that do not need a watcher. +.PP +See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR +OWN COMPOSITE WATCHERS\*(R"\s0 idioms. +.SS "\s-1WATCHER STATES\s0" +.IX Subsection "WATCHER STATES" +There are various watcher states mentioned throughout this manual \- +active, pending and so on. In this section these states and the rules to +transition between them will be described in more detail \- and while these +rules might look complicated, they usually do \*(L"the right thing\*(R". +.IP "initialised" 4 +.IX Item "initialised" +Before a watcher can be registered with the event loop it has to be +initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to +\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function. +.Sp +In this state it is simply some block of memory that is suitable for +use in an event loop. It can be moved around, freed, reused etc. at +will \- as long as you either keep the memory contents intact, or call +\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again. +.IP "started/running/active" 4 +.IX Item "started/running/active" +Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes +property of the event loop, and is actively waiting for events. While in +this state it cannot be accessed (except in a few documented ways), moved, +freed or anything else \- the only legal thing is to keep a pointer to it, +and call libev functions on it that are documented to work on active watchers. +.IP "pending" 4 +.IX Item "pending" +If a watcher is active and libev determines that an event it is interested +in has occurred (such as a timer expiring), it will become pending. It will +stay in this pending state until either it is stopped or its callback is +about to be invoked, so it is not normally pending inside the watcher +callback. +.Sp +The watcher might or might not be active while it is pending (for example, +an expired non-repeating timer can be pending but no longer active). If it +is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR), +but it is still property of the event loop at this time, so cannot be +moved, freed or reused. And if it is active the rules described in the +previous item still apply. +.Sp +It is also possible to feed an event on a watcher that is not active (e.g. +via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being +active. +.IP "stopped" 4 +.IX Item "stopped" +A watcher can be stopped implicitly by libev (in which case it might still +be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The +latter will clear any pending state the watcher might be in, regardless +of whether it was active or not, so stopping a watcher explicitly before +freeing it is often a good idea. +.Sp +While stopped (and not pending) the watcher is essentially in the +initialised state, that is, it can be reused, moved, modified in any way +you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR +it again). +.SS "\s-1WATCHER PRIORITY MODELS\s0" +.IX Subsection "WATCHER PRIORITY MODELS" +Many event loops support \fIwatcher priorities\fR, which are usually small +integers that influence the ordering of event callback invocation +between watchers in some way, all else being equal. +.PP +In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its +description for the more technical details such as the actual priority +range. +.PP +There are two common ways how these these priorities are being interpreted +by event loops: +.PP +In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation +of lower priority watchers, which means as long as higher priority +watchers receive events, lower priority watchers are not being invoked. +.PP +The less common only-for-ordering model uses priorities solely to order +callback invocation within a single event loop iteration: Higher priority +watchers are invoked before lower priority ones, but they all get invoked +before polling for new events. +.PP +Libev uses the second (only-for-ordering) model for all its watchers +except for idle watchers (which use the lock-out model). +.PP +The rationale behind this is that implementing the lock-out model for +watchers is not well supported by most kernel interfaces, and most event +libraries will just poll for the same events again and again as long as +their callbacks have not been executed, which is very inefficient in the +common case of one high-priority watcher locking out a mass of lower +priority ones. +.PP +Static (ordering) priorities are most useful when you have two or more +watchers handling the same resource: a typical usage example is having an +\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle +timeouts. Under load, data might be received while the program handles +other jobs, but since timers normally get invoked first, the timeout +handler will be executed before checking for data. In that case, giving +the timer a lower priority than the I/O watcher ensures that I/O will be +handled first even under adverse conditions (which is usually, but not +always, what you want). +.PP +Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers +will only be executed when no same or higher priority watchers have +received events, they can be used to implement the \*(L"lock-out\*(R" model when +required. +.PP +For example, to emulate how many other event libraries handle priorities, +you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in +the normal watcher callback, you just start the idle watcher. The real +processing is done in the idle watcher callback. This causes libev to +continuously poll and process kernel event data for the watcher, but when +the lock-out case is known to be rare (which in turn is rare :), this is +workable. +.PP +Usually, however, the lock-out model implemented that way will perform +miserably under the type of load it was designed to handle. In that case, +it might be preferable to stop the real watcher before starting the +idle watcher, so the kernel will not have to process the event in case +the actual processing will be delayed for considerable time. +.PP +Here is an example of an I/O watcher that should run at a strictly lower +priority than the default, and which should only process data when no +other events are pending: +.PP +.Vb 2 +\& ev_idle idle; // actual processing watcher +\& ev_io io; // actual event watcher +\& +\& static void +\& io_cb (EV_P_ ev_io *w, int revents) +\& { +\& // stop the I/O watcher, we received the event, but +\& // are not yet ready to handle it. +\& ev_io_stop (EV_A_ w); +\& +\& // start the idle watcher to handle the actual event. +\& // it will not be executed as long as other watchers +\& // with the default priority are receiving events. +\& ev_idle_start (EV_A_ &idle); +\& } +\& +\& static void +\& idle_cb (EV_P_ ev_idle *w, int revents) +\& { +\& // actual processing +\& read (STDIN_FILENO, ...); +\& +\& // have to start the I/O watcher again, as +\& // we have handled the event +\& ev_io_start (EV_P_ &io); +\& } +\& +\& // initialisation +\& ev_idle_init (&idle, idle_cb); +\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ); +\& ev_io_start (EV_DEFAULT_ &io); +.Ve +.PP +In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that +low-priority connections can not be locked out forever under load. This +enables your program to keep a lower latency for important connections +during short periods of high load, while not completely locking out less +important ones. +.SH "WATCHER TYPES" +.IX Header "WATCHER TYPES" +This section describes each watcher in detail, but will not repeat +information given in the last section. Any initialisation/set macros, +functions and members specific to the watcher type are explained. +.PP +Most members are additionally marked with either \fI[read\-only]\fR, meaning +that, while the watcher is active, you can look at the member and expect +some sensible content, but you must not modify it (you can modify it while +the watcher is stopped to your hearts content), or \fI[read\-write]\fR, which +means you can expect it to have some sensible content while the watcher is +active, but you can also modify it (within the same thread as the event +loop, i.e. without creating data races). Modifying it may not do something +sensible or take immediate effect (or do anything at all), but libev will +not crash or malfunction in any way. +.PP +In any case, the documentation for each member will explain what the +effects are, and if there are any additional access restrictions. +.ie n .SS """ev_io"" \- is this file descriptor readable or writable?" +.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?" +.IX Subsection "ev_io - is this file descriptor readable or writable?" +I/O watchers check whether a file descriptor is readable or writable +in each iteration of the event loop, or, more precisely, when reading +would not block the process and writing would at least be able to write +some data. This behaviour is called level-triggering because you keep +receiving events as long as the condition persists. Remember you can stop +the watcher if you don't want to act on the event and neither want to +receive future events. +.PP +In general you can register as many read and/or write event watchers per +fd as you want (as long as you don't confuse yourself). Setting all file +descriptors to non-blocking mode is also usually a good idea (but not +required if you know what you are doing). +.PP +Another thing you have to watch out for is that it is quite easy to +receive \*(L"spurious\*(R" readiness notifications, that is, your callback might +be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block +because there is no data. It is very easy to get into this situation even +with a relatively standard program structure. Thus it is best to always +use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far +preferable to a program hanging until some data arrives. +.PP +If you cannot run the fd in non-blocking mode (for example you should +not play around with an Xlib connection), then you have to separately +re-test whether a file descriptor is really ready with a known-to-be good +interface such as poll (fortunately in the case of Xlib, it already does +this on its own, so its quite safe to use). Some people additionally +use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block +indefinitely. +.PP +But really, best use non-blocking mode. +.PP +\fIThe special problem of disappearing file descriptors\fR +.IX Subsection "The special problem of disappearing file descriptors" +.PP +Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing +a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other +means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some +file descriptor, but when it goes away, the operating system will silently +drop this interest. If another file descriptor with the same number then +is registered with libev, there is no efficient way to see that this is, +in fact, a different file descriptor. +.PP +To avoid having to explicitly tell libev about such cases, libev follows +the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev +will assume that this is potentially a new file descriptor, otherwise +it is assumed that the file descriptor stays the same. That means that +you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the +descriptor even if the file descriptor number itself did not change. +.PP +This is how one would do it normally anyway, the important point is that +the libev application should not optimise around libev but should leave +optimisations to libev. +.PP +\fIThe special problem of dup'ed file descriptors\fR +.IX Subsection "The special problem of dup'ed file descriptors" +.PP +Some backends (e.g. epoll), cannot register events for file descriptors, +but only events for the underlying file descriptions. That means when you +have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register +events for them, only one file descriptor might actually receive events. +.PP +There is no workaround possible except not registering events +for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to +\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.PP +\fIThe special problem of files\fR +.IX Subsection "The special problem of files" +.PP +Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors +representing files, and expect it to become ready when their program +doesn't block on disk accesses (which can take a long time on their own). +.PP +However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness +notification as soon as the kernel knows whether and how much data is +there, and in the case of open files, that's always the case, so you +always get a readiness notification instantly, and your read (or possibly +write) will still block on the disk I/O. +.PP +Another way to view it is that in the case of sockets, pipes, character +devices and so on, there is another party (the sender) that delivers data +on its own, but in the case of files, there is no such thing: the disk +will not send data on its own, simply because it doesn't know what you +wish to read \- you would first have to request some data. +.PP +Since files are typically not-so-well supported by advanced notification +mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect +to files, even though you should not use it. The reason for this is +convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is +usually a tty, often a pipe, but also sometimes files or special devices +(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with +\&\fI/dev/urandom\fR), and even though the file might better be served with +asynchronous I/O instead of with non-blocking I/O, it is still useful when +it \*(L"just works\*(R" instead of freezing. +.PP +So avoid file descriptors pointing to files when you know it (e.g. use +libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or +when you rarely read from a file instead of from a socket, and want to +reuse the same code path. +.PP +\fIThe special problem of fork\fR +.IX Subsection "The special problem of fork" +.PP +Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR +at all or exhibit useless behaviour. Libev fully supports fork, but needs +to be told about it in the child if you want to continue to use it in the +child. +.PP +To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork +()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to +\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.PP +\fIThe special problem of \s-1SIGPIPE\s0\fR +.IX Subsection "The special problem of SIGPIPE" +.PP +While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR: +when writing to a pipe whose other end has been closed, your program gets +sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs +this is sensible behaviour, for daemons, this is usually undesirable. +.PP +So when you encounter spurious, unexplained daemon exits, make sure you +ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon +somewhere, as that would have given you a big clue). +.PP +\fIThe special problem of \f(BIaccept()\fIing when you can't\fR +.IX Subsection "The special problem of accept()ing when you can't" +.PP +Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example, +found in post\-2004 Linux) have the peculiar behaviour of not removing a +connection from the pending queue in all error cases. +.PP +For example, larger servers often run out of file descriptors (because +of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not +rejecting the connection, leading to libev signalling readiness on +the next iteration again (the connection still exists after all), and +typically causing the program to loop at 100% \s-1CPU\s0 usage. +.PP +Unfortunately, the set of errors that cause this issue differs between +operating systems, there is usually little the app can do to remedy the +situation, and no known thread-safe method of removing the connection to +cope with overload is known (to me). +.PP +One of the easiest ways to handle this situation is to just ignore it +\&\- when the program encounters an overload, it will just loop until the +situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an +event-based way to handle this situation, so it's the best one can do. +.PP +A better way to handle the situation is to log any errors other than +\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such +messages, and continue as usual, which at least gives the user an idea of +what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop +the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0 +usage. +.PP +If your program is single-threaded, then you could also keep a dummy file +descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and +when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR, +close that fd, and create a new dummy fd. This will gracefully refuse +clients under typical overload conditions. +.PP +The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as +is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy +opportunity for a DoS attack. +.PP +\fIWatcher-Specific Functions\fR +.IX Subsection "Watcher-Specific Functions" +.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 +.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" +.PD 0 +.IP "ev_io_set (ev_io *, int fd, int events)" 4 +.IX Item "ev_io_set (ev_io *, int fd, int events)" +.PD +Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to +receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR, both +\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR or \f(CW0\fR, to express the desire to receive the given +events. +.Sp +Note that setting the \f(CW\*(C`events\*(C'\fR to \f(CW0\fR and starting the watcher is +supported, but not specially optimized \- if your program sometimes happens +to generate this combination this is fine, but if it is easy to avoid +starting an io watcher watching for no events you should do so. +.IP "ev_io_modify (ev_io *, int events)" 4 +.IX Item "ev_io_modify (ev_io *, int events)" +Similar to \f(CW\*(C`ev_io_set\*(C'\fR, but only changes the requested events. Using this +might be faster with some backends, as libev can assume that the \f(CW\*(C`fd\*(C'\fR +still refers to the same underlying file description, something it cannot +do when using \f(CW\*(C`ev_io_set\*(C'\fR. +.IP "int fd [no\-modify]" 4 +.IX Item "int fd [no-modify]" +The file descriptor being watched. While it can be read at any time, you +must not modify this member even when the watcher is stopped \- always use +\&\f(CW\*(C`ev_io_set\*(C'\fR for that. +.IP "int events [no\-modify]" 4 +.IX Item "int events [no-modify]" +The set of events the fd is being watched for, among other flags. Remember +that this is a bit set \- to test for \f(CW\*(C`EV_READ\*(C'\fR, use \f(CW\*(C`w\->events & +EV_READ\*(C'\fR, and similarly for \f(CW\*(C`EV_WRITE\*(C'\fR. +.Sp +As with \f(CW\*(C`fd\*(C'\fR, you must not modify this member even when the watcher is +stopped, always use \f(CW\*(C`ev_io_set\*(C'\fR or \f(CW\*(C`ev_io_modify\*(C'\fR for that. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well +readable, but only once. Since it is likely line-buffered, you could +attempt to read a whole line in the callback. +.PP +.Vb 6 +\& static void +\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents) +\& { +\& ev_io_stop (loop, w); +\& .. read from stdin here (or from w\->fd) and handle any I/O errors +\& } +\& +\& ... +\& struct ev_loop *loop = ev_default_init (0); +\& ev_io stdin_readable; +\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); +\& ev_io_start (loop, &stdin_readable); +\& ev_run (loop, 0); +.Ve +.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts" +.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts" +.IX Subsection "ev_timer - relative and optionally repeating timeouts" +Timer watchers are simple relative timers that generate an event after a +given time, and optionally repeating in regular intervals after that. +.PP +The timers are based on real time, that is, if you register an event that +times out after an hour and you reset your system clock to January last +year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because +detecting time jumps is hard, and some inaccuracies are unavoidable (the +monotonic clock option helps a lot here). +.PP +The callback is guaranteed to be invoked only \fIafter\fR its timeout has +passed (not \fIat\fR, so on systems with very low-resolution clocks this +might introduce a small delay, see \*(L"the special problem of being too +early\*(R", below). If multiple timers become ready during the same loop +iteration then the ones with earlier time-out values are invoked before +ones of the same priority with later time-out values (but this is no +longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively). +.PP +\fIBe smart about timeouts\fR +.IX Subsection "Be smart about timeouts" +.PP +Many real-world problems involve some kind of timeout, usually for error +recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs, +you want to raise some error after a while. +.PP +What follows are some ways to handle this problem, from obvious and +inefficient to smart and efficient. +.PP +In the following, a 60 second activity timeout is assumed \- a timeout that +gets reset to 60 seconds each time there is activity (e.g. each time some +data or other life sign was received). +.IP "1. Use a timer and stop, reinitialise and start it on activity." 4 +.IX Item "1. Use a timer and stop, reinitialise and start it on activity." +This is the most obvious, but not the most simple way: In the beginning, +start the watcher: +.Sp +.Vb 2 +\& ev_timer_init (timer, callback, 60., 0.); +\& ev_timer_start (loop, timer); +.Ve +.Sp +Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it +and start it again: +.Sp +.Vb 3 +\& ev_timer_stop (loop, timer); +\& ev_timer_set (timer, 60., 0.); +\& ev_timer_start (loop, timer); +.Ve +.Sp +This is relatively simple to implement, but means that each time there is +some activity, libev will first have to remove the timer from its internal +data structure and then add it again. Libev tries to be fast, but it's +still not a constant-time operation. +.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4 +.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4 +.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity." +This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of +\&\f(CW\*(C`ev_timer_start\*(C'\fR. +.Sp +To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value +of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you +successfully read or write some data. If you go into an idle state where +you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR +the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be. +.Sp +That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the +\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR +member and \f(CW\*(C`ev_timer_again\*(C'\fR. +.Sp +At start: +.Sp +.Vb 3 +\& ev_init (timer, callback); +\& timer\->repeat = 60.; +\& ev_timer_again (loop, timer); +.Ve +.Sp +Each time there is some activity: +.Sp +.Vb 1 +\& ev_timer_again (loop, timer); +.Ve +.Sp +It is even possible to change the time-out on the fly, regardless of +whether the watcher is active or not: +.Sp +.Vb 2 +\& timer\->repeat = 30.; +\& ev_timer_again (loop, timer); +.Ve +.Sp +This is slightly more efficient then stopping/starting the timer each time +you want to modify its timeout value, as libev does not have to completely +remove and re-insert the timer from/into its internal data structure. +.Sp +It is, however, even simpler than the \*(L"obvious\*(R" way to do it. +.IP "3. Let the timer time out, but then re-arm it as required." 4 +.IX Item "3. Let the timer time out, but then re-arm it as required." +This method is more tricky, but usually most efficient: Most timeouts are +relatively long compared to the intervals between other activity \- in +our example, within 60 seconds, there are usually many I/O events with +associated activity resets. +.Sp +In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone, +but remember the time of last activity, and check for a real timeout only +within the callback: +.Sp +.Vb 3 +\& ev_tstamp timeout = 60.; +\& ev_tstamp last_activity; // time of last activity +\& ev_timer timer; +\& +\& static void +\& callback (EV_P_ ev_timer *w, int revents) +\& { +\& // calculate when the timeout would happen +\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout; +\& +\& // if negative, it means we the timeout already occurred +\& if (after < 0.) +\& { +\& // timeout occurred, take action +\& } +\& else +\& { +\& // callback was invoked, but there was some recent +\& // activity. simply restart the timer to time out +\& // after "after" seconds, which is the earliest time +\& // the timeout can occur. +\& ev_timer_set (w, after, 0.); +\& ev_timer_start (EV_A_ w); +\& } +\& } +.Ve +.Sp +To summarise the callback: first calculate in how many seconds the +timeout will occur (by calculating the absolute time when it would occur, +\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now +(EV_A)\*(C'\fR from that). +.Sp +If this value is negative, then we are already past the timeout, i.e. we +timed out, and need to do whatever is needed in this case. +.Sp +Otherwise, we now the earliest time at which the timeout would trigger, +and simply start the timer with this timeout value. +.Sp +In other words, each time the callback is invoked it will check whether +the timeout occurred. If not, it will simply reschedule itself to check +again at the earliest time it could time out. Rinse. Repeat. +.Sp +This scheme causes more callback invocations (about one every 60 seconds +minus half the average time between activity), but virtually no calls to +libev to change the timeout. +.Sp +To start the machinery, simply initialise the watcher and set +\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just +now), then call the callback, which will \*(L"do the right thing\*(R" and start +the timer: +.Sp +.Vb 3 +\& last_activity = ev_now (EV_A); +\& ev_init (&timer, callback); +\& callback (EV_A_ &timer, 0); +.Ve +.Sp +When there is some activity, simply store the current time in +\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all: +.Sp +.Vb 2 +\& if (activity detected) +\& last_activity = ev_now (EV_A); +.Ve +.Sp +When your timeout value changes, then the timeout can be changed by simply +providing a new value, stopping the timer and calling the callback, which +will again do the right thing (for example, time out immediately :). +.Sp +.Vb 3 +\& timeout = new_value; +\& ev_timer_stop (EV_A_ &timer); +\& callback (EV_A_ &timer, 0); +.Ve +.Sp +This technique is slightly more complex, but in most cases where the +time-out is unlikely to be triggered, much more efficient. +.IP "4. Wee, just use a double-linked list for your timeouts." 4 +.IX Item "4. Wee, just use a double-linked list for your timeouts." +If there is not one request, but many thousands (millions...), all +employing some kind of timeout with the same timeout value, then one can +do even better: +.Sp +When starting the timeout, calculate the timeout value and put the timeout +at the \fIend\fR of the list. +.Sp +Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of +the list is expected to fire (for example, using the technique #3). +.Sp +When there is some activity, remove the timer from the list, recalculate +the timeout, append it to the end of the list again, and make sure to +update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list. +.Sp +This way, one can manage an unlimited number of timeouts in O(1) time for +starting, stopping and updating the timers, at the expense of a major +complication, and having to use a constant timeout. The constant timeout +ensures that the list stays sorted. +.PP +So which method the best? +.PP +Method #2 is a simple no-brain-required solution that is adequate in most +situations. Method #3 requires a bit more thinking, but handles many cases +better, and isn't very complicated either. In most case, choosing either +one is fine, with #3 being better in typical situations. +.PP +Method #1 is almost always a bad idea, and buys you nothing. Method #4 is +rather complicated, but extremely efficient, something that really pays +off after the first million or so of active timers, i.e. it's usually +overkill :) +.PP +\fIThe special problem of being too early\fR +.IX Subsection "The special problem of being too early" +.PP +If you ask a timer to call your callback after three seconds, then +you expect it to be invoked after three seconds \- but of course, this +cannot be guaranteed to infinite precision. Less obviously, it cannot be +guaranteed to any precision by libev \- imagine somebody suspending the +process with a \s-1STOP\s0 signal for a few hours for example. +.PP +So, libev tries to invoke your callback as soon as possible \fIafter\fR the +delay has occurred, but cannot guarantee this. +.PP +A less obvious failure mode is calling your callback too early: many event +loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but +this can cause your callback to be invoked much earlier than you would +expect. +.PP +To see why, imagine a system with a clock that only offers full second +resolution (think windows if you can't come up with a broken enough \s-1OS\s0 +yourself). If you schedule a one-second timer at the time 500.9, then the +event loop will schedule your timeout to elapse at a system time of 500 +(500.9 truncated to the resolution) + 1, or 501. +.PP +If an event library looks at the timeout 0.1s later, it will see \*(L"501 >= +501\*(R" and invoke the callback 0.1s after it was started, even though a +one-second delay was requested \- this is being \*(L"too early\*(R", despite best +intentions. +.PP +This is the reason why libev will never invoke the callback if the elapsed +delay equals the requested delay, but only when the elapsed delay is +larger than the requested delay. In the example above, libev would only invoke +the callback at system time 502, or 1.1s after the timer was started. +.PP +So, while libev cannot guarantee that your callback will be invoked +exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested +delay has actually elapsed, or in other words, it always errs on the \*(L"too +late\*(R" side of things. +.PP +\fIThe special problem of time updates\fR +.IX Subsection "The special problem of time updates" +.PP +Establishing the current time is a costly operation (it usually takes +at least one system call): \s-1EV\s0 therefore updates its idea of the current +time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a +growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling +lots of events in one iteration. +.PP +The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR +time. This is usually the right thing as this timestamp refers to the time +of the event triggering whatever timeout you are modifying/starting. If +you suspect event processing to be delayed and you \fIneed\fR to base the +timeout on the current time, use something like the following to adjust +for it: +.PP +.Vb 1 +\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.); +.Ve +.PP +If the event loop is suspended for a long time, you can also force an +update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update +()\*(C'\fR, although that will push the event time of all outstanding events +further into the future. +.PP +\fIThe special problem of unsynchronised clocks\fR +.IX Subsection "The special problem of unsynchronised clocks" +.PP +Modern systems have a variety of clocks \- libev itself uses the normal +\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time +jumps). +.PP +Neither of these clocks is synchronised with each other or any other clock +on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time +than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example, +a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher +than a directly following call to \f(CW\*(C`time\*(C'\fR. +.PP +The moral of this is to only compare libev-related timestamps with +\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than +a second or so. +.PP +One more problem arises due to this lack of synchronisation: if libev uses +the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR +or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is +invoked, you will find that sometimes the callback is a bit \*(L"early\*(R". +.PP +This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so +libev makes sure your callback is not invoked before the delay happened, +\&\fImeasured according to the real time\fR, not the system clock. +.PP +If your timeouts are based on a physical timescale (e.g. \*(L"time out this +connection after 100 seconds\*(R") then this shouldn't bother you as it is +exactly the right behaviour. +.PP +If you want to compare wall clock/system timestamps to your timers, then +you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock +time, where your comparisons will always generate correct results. +.PP +\fIThe special problems of suspended animation\fR +.IX Subsection "The special problems of suspended animation" +.PP +When you leave the server world it is quite customary to hit machines that +can suspend/hibernate \- what happens to the clocks during such a suspend? +.PP +Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes +all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue +to run until the system is suspended, but they will not advance while the +system is suspended. That means, on resume, it will be as if the program +was frozen for a few seconds, but the suspend time will not be counted +towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time +clock advanced as expected, but if it is used as sole clocksource, then a +long suspend would be detected as a time jump by libev, and timers would +be adjusted accordingly. +.PP +I would not be surprised to see different behaviour in different between +operating systems, \s-1OS\s0 versions or even different hardware. +.PP +The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a +time jump in the monotonic clocks and the realtime clock. If the program +is suspended for a very long time, and monotonic clock sources are in use, +then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time +will be counted towards the timers. When no monotonic clock source is in +use, then libev will again assume a timejump and adjust accordingly. +.PP +It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR +and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get +deterministic behaviour in this case (you can do nothing against +\&\f(CW\*(C`SIGSTOP\*(C'\fR). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 +.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" +.PD 0 +.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 +.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" +.PD +Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and +negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will +automatically be stopped once the timeout is reached. If it is positive, +then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR +seconds later, again, and again, until stopped manually. +.Sp +The timer itself will do a best-effort at avoiding drift, that is, if +you configure a timer to trigger every 10 seconds, then it will normally +trigger at exactly 10 second intervals. If, however, your program cannot +keep up with the timer (because it takes longer than those 10 seconds to +do stuff) the timer will not fire more than once per event loop iteration. +.IP "ev_timer_again (loop, ev_timer *)" 4 +.IX Item "ev_timer_again (loop, ev_timer *)" +This will act as if the timer timed out, and restarts it again if it is +repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the +timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR. +.Sp +The exact semantics are as in the following rules, all of which will be +applied to the watcher: +.RS 4 +.IP "If the timer is pending, the pending status is always cleared." 4 +.IX Item "If the timer is pending, the pending status is always cleared." +.PD 0 +.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4 +.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." +.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4 +.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4 +.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary." +.RE +.RS 4 +.PD +.Sp +This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a +usage example. +.RE +.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4 +.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)" +Returns the remaining time until a timer fires. If the timer is active, +then this time is relative to the current event loop time, otherwise it's +the timeout value currently configured. +.Sp +That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns +\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR +will return \f(CW4\fR. When the timer expires and is restarted, it will return +roughly \f(CW7\fR (likely slightly less as callback invocation takes some time, +too), and so on. +.IP "ev_tstamp repeat [read\-write]" 4 +.IX Item "ev_tstamp repeat [read-write]" +The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out +or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any), +which is also when any modifications are taken into account. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Create a timer that fires after 60 seconds. +.PP +.Vb 5 +\& static void +\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents) +\& { +\& .. one minute over, w is actually stopped right here +\& } +\& +\& ev_timer mytimer; +\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); +\& ev_timer_start (loop, &mytimer); +.Ve +.PP +Example: Create a timeout timer that times out after 10 seconds of +inactivity. +.PP +.Vb 5 +\& static void +\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents) +\& { +\& .. ten seconds without any activity +\& } +\& +\& ev_timer mytimer; +\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ +\& ev_timer_again (&mytimer); /* start timer */ +\& ev_run (loop, 0); +\& +\& // and in some piece of code that gets executed on any "activity": +\& // reset the timeout to start ticking again at 10 seconds +\& ev_timer_again (&mytimer); +.Ve +.ie n .SS """ev_periodic"" \- to cron or not to cron?" +.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?" +.IX Subsection "ev_periodic - to cron or not to cron?" +Periodic watchers are also timers of a kind, but they are very versatile +(and unfortunately a bit complex). +.PP +Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or +relative time, the physical time that passes) but on wall clock time +(absolute time, the thing you can read on your calendar or clock). The +difference is that wall clock time can run faster or slower than real +time, and time jumps are not uncommon (e.g. when you adjust your +wrist-watch). +.PP +You can tell a periodic watcher to trigger after some specific point +in time: for example, if you tell a periodic watcher to trigger \*(L"in 10 +seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time +not a delay) and then reset your system clock to January of the previous +year, then it will take a year or more to trigger the event (unlike an +\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting +it, as it uses a relative timeout). +.PP +\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex +timers, such as triggering an event on each \*(L"midnight, local time\*(R", or +other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR +watchers, as those cannot react to time jumps. +.PP +As with timers, the callback is guaranteed to be invoked only when the +point in time where it is supposed to trigger has passed. If multiple +timers become ready during the same loop iteration then the ones with +earlier time-out values are invoked before ones with later time-out values +(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4 +.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" +.PD 0 +.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4 +.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" +.PD +Lots of arguments, let's sort it out... There are basically three modes of +operation, and we will explain them from simplest to most complex: +.RS 4 +.IP "\(bu" 4 +absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0) +.Sp +In this configuration the watcher triggers an event after the wall clock +time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a +time jump occurs, that is, if it is to be run at January 1st 2011 then it +will be stopped and invoked when the system clock reaches or surpasses +this point in time. +.IP "\(bu" 4 +repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0) +.Sp +In this mode the watcher will always be scheduled to time out at the next +\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be +negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR +argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods. +.Sp +This can be used to create timers that do not drift with respect to the +system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each +hour, on the hour (with respect to \s-1UTC\s0): +.Sp +.Vb 1 +\& ev_periodic_set (&periodic, 0., 3600., 0); +.Ve +.Sp +This doesn't mean there will always be 3600 seconds in between triggers, +but only that the callback will be called when the system time shows a +full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible +by 3600. +.Sp +Another way to think about it (for the mathematically inclined) is that +\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible +time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps. +.Sp +The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the +interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100 +microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have +at most a similar magnitude as the current time (say, within a factor of +ten). Typical values for offset are, in fact, \f(CW0\fR or something between +\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range. +.Sp +Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0 +speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability +will of course deteriorate. Libev itself tries to be exact to be about one +millisecond (if the \s-1OS\s0 supports it and the machine is fast enough). +.IP "\(bu" 4 +manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback) +.Sp +In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being +ignored. Instead, each time the periodic watcher gets scheduled, the +reschedule callback will be called with the watcher as first, and the +current time as second argument. +.Sp +\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever, +or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly +allowed by documentation here\fR. +.Sp +If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop +it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the +only event loop modification you are allowed to do). +.Sp +The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic +*w, ev_tstamp now)\*(C'\fR, e.g.: +.Sp +.Vb 5 +\& static ev_tstamp +\& my_rescheduler (ev_periodic *w, ev_tstamp now) +\& { +\& return now + 60.; +\& } +.Ve +.Sp +It must return the next time to trigger, based on the passed time value +(that is, the lowest time value larger than to the second argument). It +will usually be called just before the callback will be triggered, but +might be called at other times, too. +.Sp +\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or +equal to the passed \f(CI\*(C`now\*(C'\fI value\fR. +.Sp +This can be used to create very complex timers, such as a timer that +triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate +the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for +this. Here is a (completely untested, no error checking) example on how to +do this: +.Sp +.Vb 1 +\& #include <time.h> +\& +\& static ev_tstamp +\& my_rescheduler (ev_periodic *w, ev_tstamp now) +\& { +\& time_t tnow = (time_t)now; +\& struct tm tm; +\& localtime_r (&tnow, &tm); +\& +\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day +\& ++tm.tm_mday; // midnight next day +\& +\& return mktime (&tm); +\& } +.Ve +.Sp +Note: this code might run into trouble on days that have more then two +midnights (beginning and end). +.RE +.RS 4 +.RE +.IP "ev_periodic_again (loop, ev_periodic *)" 4 +.IX Item "ev_periodic_again (loop, ev_periodic *)" +Simply stops and restarts the periodic watcher again. This is only useful +when you changed some parameters or the reschedule callback would return +a different time than the last time it was called (e.g. in a crond like +program when the crontabs have changed). +.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4 +.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)" +When active, returns the absolute time that the watcher is supposed +to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to +\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual +rescheduling modes. +.IP "ev_tstamp offset [read\-write]" 4 +.IX Item "ev_tstamp offset [read-write]" +When repeating, this contains the offset value, otherwise this is the +absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR, +although libev might modify this value for better numerical stability). +.Sp +Can be modified any time, but changes only take effect when the periodic +timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. +.IP "ev_tstamp interval [read\-write]" 4 +.IX Item "ev_tstamp interval [read-write]" +The current interval value. Can be modified any time, but changes only +take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being +called. +.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4 +.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]" +The current reschedule callback, or \f(CW0\fR, if this functionality is +switched off. Can be changed any time, but changes only take effect when +the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Call a callback every hour, or, more precisely, whenever the +system time is divisible by 3600. The callback invocation times have +potentially a lot of jitter, but good long-term stability. +.PP +.Vb 5 +\& static void +\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents) +\& { +\& ... its now a full hour (UTC, or TAI or whatever your clock follows) +\& } +\& +\& ev_periodic hourly_tick; +\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); +\& ev_periodic_start (loop, &hourly_tick); +.Ve +.PP +Example: The same as above, but use a reschedule callback to do it: +.PP +.Vb 1 +\& #include <math.h> +\& +\& static ev_tstamp +\& my_scheduler_cb (ev_periodic *w, ev_tstamp now) +\& { +\& return now + (3600. \- fmod (now, 3600.)); +\& } +\& +\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); +.Ve +.PP +Example: Call a callback every hour, starting now: +.PP +.Vb 4 +\& ev_periodic hourly_tick; +\& ev_periodic_init (&hourly_tick, clock_cb, +\& fmod (ev_now (loop), 3600.), 3600., 0); +\& ev_periodic_start (loop, &hourly_tick); +.Ve +.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!" +.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!" +.IX Subsection "ev_signal - signal me when a signal gets signalled!" +Signal watchers will trigger an event when the process receives a specific +signal one or more times. Even though signals are very asynchronous, libev +will try its best to deliver signals synchronously, i.e. as part of the +normal event processing, like any other event. +.PP +If you want signals to be delivered truly asynchronously, just use +\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing +the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to +synchronously wake up an event loop. +.PP +You can configure as many watchers as you like for the same signal, but +only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your +default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for +\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At +the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop. +.PP +Only after the first watcher for a signal is started will libev actually +register something with the kernel. It thus coexists with your own signal +handlers as long as you don't register any with libev for the same signal. +.PP +If possible and supported, libev will install its handlers with +\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should +not be unduly interrupted. If you have a problem with system calls getting +interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher +and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher. +.PP +\fIThe special problem of inheritance over fork/execve/pthread_create\fR +.IX Subsection "The special problem of inheritance over fork/execve/pthread_create" +.PP +Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition +(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after +stopping it again), that is, libev might or might not block the signal, +and might or might not set or restore the installed signal handler (but +see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR). +.PP +While this does not matter for the signal disposition (libev never +sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on +\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect +certain signals to be blocked. +.PP +This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset +the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good +choice usually). +.PP +The simplest way to ensure that the signal mask is reset in the child is +to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will +catch fork calls done by libraries (such as the libc) as well. +.PP +In current versions of libev, the signal will not be blocked indefinitely +unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces +the window of opportunity for problems, it will not go away, as libev +\&\fIhas\fR to modify the signal mask, at least temporarily. +.PP +So I can't stress this enough: \fIIf you do not reset your signal mask when +you expect it to be empty, you have a race condition in your code\fR. This +is not a libev-specific thing, this is true for most event libraries. +.PP +\fIThe special problem of threads signal handling\fR +.IX Subsection "The special problem of threads signal handling" +.PP +\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically, +a lot of functionality (sigfd, sigwait etc.) only really works if all +threads in a process block signals, which is hard to achieve. +.PP +When you want to use sigwait (or mix libev signal handling with your own +for the same signals), you can tackle this problem by globally blocking +all signals before creating any threads (or creating them with a fully set +sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating +loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles +these signals. You can pass on any signals that libev might be interested +in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 +.IX Item "ev_signal_init (ev_signal *, callback, int signum)" +.PD 0 +.IP "ev_signal_set (ev_signal *, int signum)" 4 +.IX Item "ev_signal_set (ev_signal *, int signum)" +.PD +Configures the watcher to trigger on the given signal number (usually one +of the \f(CW\*(C`SIGxxx\*(C'\fR constants). +.IP "int signum [read\-only]" 4 +.IX Item "int signum [read-only]" +The signal the watcher watches out for. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Try to exit cleanly on \s-1SIGINT.\s0 +.PP +.Vb 5 +\& static void +\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents) +\& { +\& ev_break (loop, EVBREAK_ALL); +\& } +\& +\& ev_signal signal_watcher; +\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); +\& ev_signal_start (loop, &signal_watcher); +.Ve +.ie n .SS """ev_child"" \- watch out for process status changes" +.el .SS "\f(CWev_child\fP \- watch out for process status changes" +.IX Subsection "ev_child - watch out for process status changes" +Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to +some child status changes (most typically when a child of yours dies or +exits). It is permissible to install a child watcher \fIafter\fR the child +has been forked (which implies it might have already exited), as long +as the event loop isn't entered (or is continued from a watcher), i.e., +forking and then immediately registering a watcher for the child is fine, +but forking and registering a watcher a few event loop iterations later or +in the next callback invocation is not. +.PP +Only the default event loop is capable of handling signals, and therefore +you can only register child watchers in the default event loop. +.PP +Due to some design glitches inside libev, child watchers will always be +handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by +libev) +.PP +\fIProcess Interaction\fR +.IX Subsection "Process Interaction" +.PP +Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is +initialised. This is necessary to guarantee proper behaviour even if the +first child watcher is started after the child exits. The occurrence +of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done +synchronously as part of the event loop processing. Libev always reaps all +children, even ones not watched. +.PP +\fIOverriding the Built-In Processing\fR +.IX Subsection "Overriding the Built-In Processing" +.PP +Libev offers no special support for overriding the built-in child +processing, but if your application collides with libev's default child +handler, you can override it easily by installing your own handler for +\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the +default loop never gets destroyed. You are encouraged, however, to use an +event-based approach to child reaping and thus use libev's support for +that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely. +.PP +\fIStopping the Child Watcher\fR +.IX Subsection "Stopping the Child Watcher" +.PP +Currently, the child watcher never gets stopped, even when the +child terminates, so normally one needs to stop the watcher in the +callback. Future versions of libev might stop the watcher automatically +when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a +problem). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4 +.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)" +.PD 0 +.IP "ev_child_set (ev_child *, int pid, int trace)" 4 +.IX Item "ev_child_set (ev_child *, int pid, int trace)" +.PD +Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or +\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look +at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see +the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems +\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the +process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only +activate the watcher when the process terminates) or \f(CW1\fR (additionally +activate the watcher when the process is stopped or continued). +.IP "int pid [read\-only]" 4 +.IX Item "int pid [read-only]" +The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. +.IP "int rpid [read\-write]" 4 +.IX Item "int rpid [read-write]" +The process id that detected a status change. +.IP "int rstatus [read\-write]" 4 +.IX Item "int rstatus [read-write]" +The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems +\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for +its completion. +.PP +.Vb 1 +\& ev_child cw; +\& +\& static void +\& child_cb (EV_P_ ev_child *w, int revents) +\& { +\& ev_child_stop (EV_A_ w); +\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus); +\& } +\& +\& pid_t pid = fork (); +\& +\& if (pid < 0) +\& // error +\& else if (pid == 0) +\& { +\& // the forked child executes here +\& exit (1); +\& } +\& else +\& { +\& ev_child_init (&cw, child_cb, pid, 0); +\& ev_child_start (EV_DEFAULT_ &cw); +\& } +.Ve +.ie n .SS """ev_stat"" \- did the file attributes just change?" +.el .SS "\f(CWev_stat\fP \- did the file attributes just change?" +.IX Subsection "ev_stat - did the file attributes just change?" +This watches a file system path for attribute changes. That is, it calls +\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed) +and sees if it changed compared to the last time, invoking the callback +if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that +happen after the watcher has been started will be reported. +.PP +The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does +not exist\*(R" is a status change like any other. The condition \*(L"path does not +exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the +\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at +least one) and all the other fields of the stat buffer having unspecified +contents. +.PP +The path \fImust not\fR end in a slash or contain special components such as +\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and +your working directory changes, then the behaviour is undefined. +.PP +Since there is no portable change notification interface available, the +portable implementation simply calls \f(CWstat(2)\fR regularly on the path +to see if it changed somehow. You can specify a recommended polling +interval for this case. If you specify a polling interval of \f(CW0\fR (highly +recommended!) then a \fIsuitable, unspecified default\fR value will be used +(which you can expect to be around five seconds, although this might +change dynamically). Libev will also impose a minimum interval which is +currently around \f(CW0.1\fR, but that's usually overkill. +.PP +This watcher type is not meant for massive numbers of stat watchers, +as even with OS-supported change notifications, this can be +resource-intensive. +.PP +At the time of this writing, the only OS-specific interface implemented +is the Linux inotify interface (implementing kqueue support is left as an +exercise for the reader. Note, however, that the author sees no way of +implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint). +.PP +\fI\s-1ABI\s0 Issues (Largefile Support)\fR +.IX Subsection "ABI Issues (Largefile Support)" +.PP +Libev by default (unless the user overrides this) uses the default +compilation environment, which means that on systems with large file +support disabled by default, you get the 32 bit version of the stat +structure. When using the library from programs that change the \s-1ABI\s0 to +use 64 bit file offsets the programs will fail. In that case you have to +compile libev with the same flags to get binary compatibility. This is +obviously the case with any flags that change the \s-1ABI,\s0 but the problem is +most noticeably displayed with ev_stat and large file support. +.PP +The solution for this is to lobby your distribution maker to make large +file interfaces available by default (as e.g. FreeBSD does) and not +optional. Libev cannot simply switch on large file support because it has +to exchange stat structures with application programs compiled using the +default compilation environment. +.PP +\fIInotify and Kqueue\fR +.IX Subsection "Inotify and Kqueue" +.PP +When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at +runtime, it will be used to speed up change detection where possible. The +inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR +watcher is being started. +.PP +Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers +except that changes might be detected earlier, and in some cases, to avoid +making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support +there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling, +but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too +many bugs), the path exists (i.e. stat succeeds), and the path resides on +a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and +xfs are fully working) libev usually gets away without polling. +.PP +There is no support for kqueue, as apparently it cannot be used to +implement this functionality, due to the requirement of having a file +descriptor open on the object at all times, and detecting renames, unlinks +etc. is difficult. +.PP +\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR +.IX Subsection "stat () is a synchronous operation" +.PP +Libev doesn't normally do any kind of I/O itself, and so is not blocking +the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat +()\*(C'\fR, which is a synchronous operation. +.PP +For local paths, this usually doesn't matter: unless the system is very +busy or the intervals between stat's are large, a stat call will be fast, +as the path data is usually in memory already (except when starting the +watcher). +.PP +For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite +time due to network issues, and even under good conditions, a stat call +often takes multiple milliseconds. +.PP +Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked +paths, although this is fully supported by libev. +.PP +\fIThe special problem of stat time resolution\fR +.IX Subsection "The special problem of stat time resolution" +.PP +The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably, +and even on systems where the resolution is higher, most file systems +still only support whole seconds. +.PP +That means that, if the time is the only thing that changes, you can +easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and +calls your callback, which does something. When there is another update +within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the +stat data does change in other ways (e.g. file size). +.PP +The solution to this is to delay acting on a change for slightly more +than a second (or till slightly after the next full second boundary), using +a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02); +ev_timer_again (loop, w)\*(C'\fR). +.PP +The \f(CW.02\fR offset is added to work around small timing inconsistencies +of some operating systems (where the second counter of the current time +might be be delayed. One such system is the Linux kernel, where a call to +\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than +a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to +update file times then there will be a small window where the kernel uses +the previous second to update file times but libev might already execute +the timer callback). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 +.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" +.PD 0 +.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 +.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" +.PD +Configures the watcher to wait for status changes of the given +\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to +be detected and should normally be specified as \f(CW0\fR to let libev choose +a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same +path for as long as the watcher is active. +.Sp +The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected, +relative to the attributes at the time the watcher was started (or the +last change was detected). +.IP "ev_stat_stat (loop, ev_stat *)" 4 +.IX Item "ev_stat_stat (loop, ev_stat *)" +Updates the stat buffer immediately with new values. If you change the +watched path in your callback, you could call this function to avoid +detecting this change (while introducing a race condition if you are not +the only one changing the path). Can also be useful simply to find out the +new values. +.IP "ev_statdata attr [read\-only]" 4 +.IX Item "ev_statdata attr [read-only]" +The most-recently detected attributes of the file. Although the type is +\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types +suitable for your system, but you can only rely on the POSIX-standardised +members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was +some error while \f(CW\*(C`stat\*(C'\fRing the file. +.IP "ev_statdata prev [read\-only]" 4 +.IX Item "ev_statdata prev [read-only]" +The previous attributes of the file. The callback gets invoked whenever +\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members +differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR, +\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR. +.IP "ev_tstamp interval [read\-only]" 4 +.IX Item "ev_tstamp interval [read-only]" +The specified interval. +.IP "const char *path [read\-only]" 4 +.IX Item "const char *path [read-only]" +The file system path that is being watched. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. +.PP +.Vb 10 +\& static void +\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) +\& { +\& /* /etc/passwd changed in some way */ +\& if (w\->attr.st_nlink) +\& { +\& printf ("passwd current size %ld\en", (long)w\->attr.st_size); +\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime); +\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime); +\& } +\& else +\& /* you shalt not abuse printf for puts */ +\& puts ("wow, /etc/passwd is not there, expect problems. " +\& "if this is windows, they already arrived\en"); +\& } +\& +\& ... +\& ev_stat passwd; +\& +\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.); +\& ev_stat_start (loop, &passwd); +.Ve +.PP +Example: Like above, but additionally use a one-second delay so we do not +miss updates (however, frequent updates will delay processing, too, so +one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on +\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation). +.PP +.Vb 2 +\& static ev_stat passwd; +\& static ev_timer timer; +\& +\& static void +\& timer_cb (EV_P_ ev_timer *w, int revents) +\& { +\& ev_timer_stop (EV_A_ w); +\& +\& /* now it\*(Aqs one second after the most recent passwd change */ +\& } +\& +\& static void +\& stat_cb (EV_P_ ev_stat *w, int revents) +\& { +\& /* reset the one\-second timer */ +\& ev_timer_again (EV_A_ &timer); +\& } +\& +\& ... +\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.); +\& ev_stat_start (loop, &passwd); +\& ev_timer_init (&timer, timer_cb, 0., 1.02); +.Ve +.ie n .SS """ev_idle"" \- when you've got nothing better to do..." +.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..." +.IX Subsection "ev_idle - when you've got nothing better to do..." +Idle watchers trigger events when no other events of the same or higher +priority are pending (prepare, check and other idle watchers do not count +as receiving \*(L"events\*(R"). +.PP +That is, as long as your process is busy handling sockets or timeouts +(or even signals, imagine) of the same or higher priority it will not be +triggered. But when your process is idle (or only lower-priority watchers +are pending), the idle watchers are being called once per event loop +iteration \- until stopped, that is, or your process receives more events +and becomes busy again with higher priority stuff. +.PP +The most noteworthy effect is that as long as any idle watchers are +active, the process will not block when waiting for new events. +.PP +Apart from keeping your process non-blocking (which is a useful +effect on its own sometimes), idle watchers are a good place to do +\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the +event loop has handled all outstanding events. +.PP +\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR +.IX Subsection "Abusing an ev_idle watcher for its side-effect" +.PP +As long as there is at least one active idle watcher, libev will never +sleep unnecessarily. Or in other words, it will loop as fast as possible. +For this to work, the idle watcher doesn't need to be invoked at all \- the +lowest priority will do. +.PP +This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher, +to do something on each event loop iteration \- for example to balance load +between different connections. +.PP +See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer +example. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_idle_init (ev_idle *, callback)" 4 +.IX Item "ev_idle_init (ev_idle *, callback)" +Initialises and configures the idle watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, +believe me. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the +callback, free it. Also, use no error checking, as usual. +.PP +.Vb 5 +\& static void +\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents) +\& { +\& // stop the watcher +\& ev_idle_stop (loop, w); +\& +\& // now we can free it +\& free (w); +\& +\& // now do something you wanted to do when the program has +\& // no longer anything immediate to do. +\& } +\& +\& ev_idle *idle_watcher = malloc (sizeof (ev_idle)); +\& ev_idle_init (idle_watcher, idle_cb); +\& ev_idle_start (loop, idle_watcher); +.Ve +.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!" +.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" +.IX Subsection "ev_prepare and ev_check - customise your event loop!" +Prepare and check watchers are often (but not always) used in pairs: +prepare watchers get invoked before the process blocks and check watchers +afterwards. +.PP +You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the +current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or +\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine, +however. The rationale behind this is that you do not need to check +for recursion in those watchers, i.e. the sequence will always be +\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each +kind they will always be called in pairs bracketing the blocking call. +.PP +Their main purpose is to integrate other event mechanisms into libev and +their use is somewhat advanced. They could be used, for example, to track +variable changes, implement your own watchers, integrate net-snmp or a +coroutine library and lots more. They are also occasionally useful if +you cache some data and want to flush it before blocking (for example, +in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR +watcher). +.PP +This is done by examining in each prepare call which file descriptors +need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers +for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many +libraries provide exactly this functionality). Then, in the check watcher, +you check for any events that occurred (by checking the pending status +of all watchers and stopping them) and call back into the library. The +I/O and timer callbacks will never actually be called (but must be valid +nevertheless, because you never know, you know?). +.PP +As another example, the Perl Coro module uses these hooks to integrate +coroutines into libev programs, by yielding to other active coroutines +during each prepare and only letting the process block if no coroutines +are ready to run (it's actually more complicated: it only runs coroutines +with priority higher than or equal to the event loop and one coroutine +of lower priority, but only once, using idle watchers to keep the event +loop from blocking if lower-priority coroutines are active, thus mapping +low-priority coroutines to idle/background tasks). +.PP +When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers +highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before +any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR +watchers). +.PP +Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not +activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they +might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As +\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event +loops those other event loops might be in an unusable state until their +\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with +others). +.PP +\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR +.IX Subsection "Abusing an ev_check watcher for its side-effect" +.PP +\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be +useful because they are called once per event loop iteration. For +example, if you want to handle a large number of connections fairly, you +normally only do a bit of work for each active connection, and if there +is more work to do, you wait for the next event loop iteration, so other +connections have a chance of making progress. +.PP +Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the +next event loop iteration. However, that isn't as soon as possible \- +without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked. +.PP +This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a +single global idle watcher that is active as long as you have one active +\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop +will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets +invoked. Neither watcher alone can do that. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_prepare_init (ev_prepare *, callback)" 4 +.IX Item "ev_prepare_init (ev_prepare *, callback)" +.PD 0 +.IP "ev_check_init (ev_check *, callback)" 4 +.IX Item "ev_check_init (ev_check *, callback)" +.PD +Initialises and configures the prepare or check watcher \- they have no +parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR +macros, but using them is utterly, utterly, utterly and completely +pointless. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +There are a number of principal ways to embed other event loops or modules +into libev. Here are some ideas on how to include libadns into libev +(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could +use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a +Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the +Glib event loop). +.PP +Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, +and in a check watcher, destroy them and call into libadns. What follows +is pseudo-code only of course. This requires you to either use a low +priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as +the callbacks for the IO/timeout watchers might not have been called yet. +.PP +.Vb 2 +\& static ev_io iow [nfd]; +\& static ev_timer tw; +\& +\& static void +\& io_cb (struct ev_loop *loop, ev_io *w, int revents) +\& { +\& } +\& +\& // create io watchers for each fd and a timer before blocking +\& static void +\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents) +\& { +\& int timeout = 3600000; +\& struct pollfd fds [nfd]; +\& // actual code will need to loop here and realloc etc. +\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); +\& +\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */ +\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.); +\& ev_timer_start (loop, &tw); +\& +\& // create one ev_io per pollfd +\& for (int i = 0; i < nfd; ++i) +\& { +\& ev_io_init (iow + i, io_cb, fds [i].fd, +\& ((fds [i].events & POLLIN ? EV_READ : 0) +\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); +\& +\& fds [i].revents = 0; +\& ev_io_start (loop, iow + i); +\& } +\& } +\& +\& // stop all watchers after blocking +\& static void +\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents) +\& { +\& ev_timer_stop (loop, &tw); +\& +\& for (int i = 0; i < nfd; ++i) +\& { +\& // set the relevant poll flags +\& // could also call adns_processreadable etc. here +\& struct pollfd *fd = fds + i; +\& int revents = ev_clear_pending (iow + i); +\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN; +\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT; +\& +\& // now stop the watcher +\& ev_io_stop (loop, iow + i); +\& } +\& +\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); +\& } +.Ve +.PP +Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR +in the prepare watcher and would dispose of the check watcher. +.PP +Method 3: If the module to be embedded supports explicit event +notification (libadns does), you can also make use of the actual watcher +callbacks, and only destroy/create the watchers in the prepare watcher. +.PP +.Vb 5 +\& static void +\& timer_cb (EV_P_ ev_timer *w, int revents) +\& { +\& adns_state ads = (adns_state)w\->data; +\& update_now (EV_A); +\& +\& adns_processtimeouts (ads, &tv_now); +\& } +\& +\& static void +\& io_cb (EV_P_ ev_io *w, int revents) +\& { +\& adns_state ads = (adns_state)w\->data; +\& update_now (EV_A); +\& +\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now); +\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now); +\& } +\& +\& // do not ever call adns_afterpoll +.Ve +.PP +Method 4: Do not use a prepare or check watcher because the module you +want to embed is not flexible enough to support it. Instead, you can +override their poll function. The drawback with this solution is that the +main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses +this approach, effectively embedding \s-1EV\s0 as a client into the horrible +libglib event loop. +.PP +.Vb 4 +\& static gint +\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) +\& { +\& int got_events = 0; +\& +\& for (n = 0; n < nfds; ++n) +\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events +\& +\& if (timeout >= 0) +\& // create/start timer +\& +\& // poll +\& ev_run (EV_A_ 0); +\& +\& // stop timer again +\& if (timeout >= 0) +\& ev_timer_stop (EV_A_ &to); +\& +\& // stop io watchers again \- their callbacks should have set +\& for (n = 0; n < nfds; ++n) +\& ev_io_stop (EV_A_ iow [n]); +\& +\& return got_events; +\& } +.Ve +.ie n .SS """ev_embed"" \- when one backend isn't enough..." +.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..." +.IX Subsection "ev_embed - when one backend isn't enough..." +This is a rather advanced watcher type that lets you embed one event loop +into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded +loop, other types of watchers might be handled in a delayed or incorrect +fashion and must not be used). +.PP +There are primarily two reasons you would want that: work around bugs and +prioritise I/O. +.PP +As an example for a bug workaround, the kqueue backend might only support +sockets on some platform, so it is unusable as generic backend, but you +still want to make use of it because you have many sockets and it scales +so nicely. In this case, you would create a kqueue-based loop and embed +it into your default loop (which might use e.g. poll). Overall operation +will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then +\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are +best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :) +.PP +As for prioritising I/O: under rare circumstances you have the case where +some fds have to be watched and handled very quickly (with low latency), +and even priorities and idle watchers might have too much overhead. In +this case you would put all the high priority stuff in one loop and all +the rest in a second one, and embed the second one in the first. +.PP +As long as the watcher is active, the callback will be invoked every +time there might be events pending in the embedded loop. The callback +must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single +sweep and invoke their callbacks (the callback doesn't need to invoke the +\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher +to give the embedded loop strictly lower priority for example). +.PP +You can also set the callback to \f(CW0\fR, in which case the embed watcher +will automatically execute the embedded loop sweep whenever necessary. +.PP +Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher +is active, i.e., the embedded loop will automatically be forked when the +embedding loop forks. In other cases, the user is responsible for calling +\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop. +.PP +Unfortunately, not all backends are embeddable: only the ones returned by +\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any +portable one. +.PP +So when you want to use this feature you will always have to be prepared +that you cannot get an embeddable loop. The recommended way to get around +this is to have a separate variables for your embeddable loop, try to +create it, and if that fails, use the normal loop for everything. +.PP +\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR +.IX Subsection "ev_embed and fork" +.PP +While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will +automatically be applied to the embedded loop as well, so no special +fork handling is required in that case. When the watcher is not running, +however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR +as applicable. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 +.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" +.PD 0 +.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4 +.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" +.PD +Configures the watcher to embed the given loop, which must be +embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be +invoked automatically, otherwise it is the responsibility of the callback +to invoke it (it will continue to be called until the sweep has been done, +if you do not want that, you need to temporarily stop the embed watcher). +.IP "ev_embed_sweep (loop, ev_embed *)" 4 +.IX Item "ev_embed_sweep (loop, ev_embed *)" +Make a single, non-blocking sweep over the embedded loop. This works +similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most +appropriate way for embedded loops. +.IP "struct ev_loop *other [read\-only]" 4 +.IX Item "struct ev_loop *other [read-only]" +The embedded event loop. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Try to get an embeddable event loop and embed it into the default +event loop. If that is not possible, use the default loop. The default +loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in +\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be +used). +.PP +.Vb 3 +\& struct ev_loop *loop_hi = ev_default_init (0); +\& struct ev_loop *loop_lo = 0; +\& ev_embed embed; +\& +\& // see if there is a chance of getting one that works +\& // (remember that a flags value of 0 means autodetection) +\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () +\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) +\& : 0; +\& +\& // if we got one, then embed it, otherwise default to loop_hi +\& if (loop_lo) +\& { +\& ev_embed_init (&embed, 0, loop_lo); +\& ev_embed_start (loop_hi, &embed); +\& } +\& else +\& loop_lo = loop_hi; +.Ve +.PP +Example: Check if kqueue is available but not recommended and create +a kqueue backend for use with sockets (which usually work with any +kqueue implementation). Store the kqueue/socket\-only event loop in +\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too). +.PP +.Vb 3 +\& struct ev_loop *loop = ev_default_init (0); +\& struct ev_loop *loop_socket = 0; +\& ev_embed embed; +\& +\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) +\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) +\& { +\& ev_embed_init (&embed, 0, loop_socket); +\& ev_embed_start (loop, &embed); +\& } +\& +\& if (!loop_socket) +\& loop_socket = loop; +\& +\& // now use loop_socket for all sockets, and loop for everything else +.Ve +.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork" +.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" +.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" +Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because +whoever is a good citizen cared to tell libev about it by calling +\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next +and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child +after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats +and calls it in the wrong process, the fork handlers will be invoked, too, +of course. +.PP +\fIThe special problem of life after fork \- how is it possible?\fR +.IX Subsection "The special problem of life after fork - how is it possible?" +.PP +Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set +up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This +sequence should be handled by libev without any problems. +.PP +This changes when the application actually wants to do event handling +in the child, or both parent in child, in effect \*(L"continuing\*(R" after the +fork. +.PP +The default mode of operation (for libev, with application help to detect +forks) is to duplicate all the state in the child, as would be expected +when \fIeither\fR the parent \fIor\fR the child process continues. +.PP +When both processes want to continue using libev, then this is usually the +wrong result. In that case, usually one process (typically the parent) is +supposed to continue with all watchers in place as before, while the other +process typically wants to start fresh, i.e. without any active watchers. +.PP +The cleanest and most efficient way to achieve that with libev is to +simply create a new event loop, which of course will be \*(L"empty\*(R", and +use that for new watchers. This has the advantage of not touching more +memory than necessary, and thus avoiding the copy-on-write, and the +disadvantage of having to use multiple event loops (which do not support +signal watchers). +.PP +When this is not possible, or you want to use the default loop for +other reasons, then in the process that wants to start \*(L"fresh\*(R", call +\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. +Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered +watchers, so you have to be careful not to execute code that modifies +those watchers. Note also that in that case, you have to re-register any +signal watchers. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_fork_init (ev_fork *, callback)" 4 +.IX Item "ev_fork_init (ev_fork *, callback)" +Initialises and configures the fork watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, +really. +.ie n .SS """ev_cleanup"" \- even the best things end" +.el .SS "\f(CWev_cleanup\fP \- even the best things end" +.IX Subsection "ev_cleanup - even the best things end" +Cleanup watchers are called just before the event loop is being destroyed +by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR. +.PP +While there is no guarantee that the event loop gets destroyed, cleanup +watchers provide a convenient method to install cleanup hooks for your +program, worker threads and so on \- you just to make sure to destroy the +loop when you want them to be invoked. +.PP +Cleanup watchers are invoked in the same way as any other watcher. Unlike +all other watchers, they do not keep a reference to the event loop (which +makes a lot of sense if you think about it). Like all other watchers, you +can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_cleanup_init (ev_cleanup *, callback)" 4 +.IX Item "ev_cleanup_init (ev_cleanup *, callback)" +Initialises and configures the cleanup watcher \- it has no parameters of +any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly +pointless, I assure you. +.PP +Example: Register an atexit handler to destroy the default loop, so any +cleanup functions are called. +.PP +.Vb 5 +\& static void +\& program_exits (void) +\& { +\& ev_loop_destroy (EV_DEFAULT_UC); +\& } +\& +\& ... +\& atexit (program_exits); +.Ve +.ie n .SS """ev_async"" \- how to wake up an event loop" +.el .SS "\f(CWev_async\fP \- how to wake up an event loop" +.IX Subsection "ev_async - how to wake up an event loop" +In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other +asynchronous sources such as signal handlers (as opposed to multiple event +loops \- those are of course safe to use in different threads). +.PP +Sometimes, however, you need to wake up an event loop you do not control, +for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR +watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal +it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe. +.PP +This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals, +too, are asynchronous in nature, and signals, too, will be compressed +(i.e. the number of callback invocations may be less than the number of +\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind +of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused +signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread, +even without knowing which loop owns the signal. +.PP +\fIQueueing\fR +.IX Subsection "Queueing" +.PP +\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason +is that the author does not know of a simple (or any) algorithm for a +multiple-writer-single-reader queue that works in all cases and doesn't +need elaborate support such as pthreads or unportable memory access +semantics. +.PP +That means that if you want to queue data, you have to provide your own +queue. But at least I can tell you how to implement locking around your +queue: +.IP "queueing from a signal handler context" 4 +.IX Item "queueing from a signal handler context" +To implement race-free queueing, you simply add to the queue in the signal +handler but you block the signal handler in the watcher callback. Here is +an example that does that for some fictitious \s-1SIGUSR1\s0 handler: +.Sp +.Vb 1 +\& static ev_async mysig; +\& +\& static void +\& sigusr1_handler (void) +\& { +\& sometype data; +\& +\& // no locking etc. +\& queue_put (data); +\& ev_async_send (EV_DEFAULT_ &mysig); +\& } +\& +\& static void +\& mysig_cb (EV_P_ ev_async *w, int revents) +\& { +\& sometype data; +\& sigset_t block, prev; +\& +\& sigemptyset (&block); +\& sigaddset (&block, SIGUSR1); +\& sigprocmask (SIG_BLOCK, &block, &prev); +\& +\& while (queue_get (&data)) +\& process (data); +\& +\& if (sigismember (&prev, SIGUSR1) +\& sigprocmask (SIG_UNBLOCK, &block, 0); +\& } +.Ve +.Sp +(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR +instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it +either...). +.IP "queueing from a thread context" 4 +.IX Item "queueing from a thread context" +The strategy for threads is different, as you cannot (easily) block +threads but you can easily preempt them, so to queue safely you need to +employ a traditional mutex lock, such as in this pthread example: +.Sp +.Vb 2 +\& static ev_async mysig; +\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER; +\& +\& static void +\& otherthread (void) +\& { +\& // only need to lock the actual queueing operation +\& pthread_mutex_lock (&mymutex); +\& queue_put (data); +\& pthread_mutex_unlock (&mymutex); +\& +\& ev_async_send (EV_DEFAULT_ &mysig); +\& } +\& +\& static void +\& mysig_cb (EV_P_ ev_async *w, int revents) +\& { +\& pthread_mutex_lock (&mymutex); +\& +\& while (queue_get (&data)) +\& process (data); +\& +\& pthread_mutex_unlock (&mymutex); +\& } +.Ve +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_async_init (ev_async *, callback)" 4 +.IX Item "ev_async_init (ev_async *, callback)" +Initialises and configures the async watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless, +trust me. +.IP "ev_async_send (loop, ev_async *)" 4 +.IX Item "ev_async_send (loop, ev_async *)" +Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds +an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly +returns. +.Sp +Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, +signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the +embedding section below on what exactly this means). +.Sp +Note that, as with other watchers in libev, multiple events might get +compressed into a single callback invocation (another way to look at +this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on +\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that). +.Sp +This call incurs the overhead of at most one extra system call per event +loop iteration, if the event loop is blocked, and no syscall at all if +the event loop (or your program) is processing events. That means that +repeated calls are basically free (there is no need to avoid calls for +performance reasons) and that the overhead becomes smaller (typically +zero) under load. +.IP "bool = ev_async_pending (ev_async *)" 4 +.IX Item "bool = ev_async_pending (ev_async *)" +Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the +watcher but the event has not yet been processed (or even noted) by the +event loop. +.Sp +\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When +the loop iterates next and checks for the watcher to have become active, +it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very +quickly check whether invoking the loop might be a good idea. +.Sp +Not that this does \fInot\fR check whether the watcher itself is pending, +only whether it has been requested to make this watcher pending: there +is a time window between the event loop checking and resetting the async +notification, and the callback being invoked. +.SH "OTHER FUNCTIONS" +.IX Header "OTHER FUNCTIONS" +There are some other functions of possible interest. Described. Here. Now. +.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4 +.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" +This function combines a simple timer and an I/O watcher, calls your +callback on whichever event happens first and automatically stops both +watchers. This is useful if you want to wait for a single event on an fd +or timeout without having to allocate/configure/start/stop/free one or +more watchers yourself. +.Sp +If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the +\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for +the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started. +.Sp +If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be +started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and +repeat = 0) will be started. \f(CW0\fR is a valid timeout. +.Sp +The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is +passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of +\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR +value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR +a timeout and an io event at the same time \- you probably should give io +events precedence. +.Sp +Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0 +.Sp +.Vb 7 +\& static void stdin_ready (int revents, void *arg) +\& { +\& if (revents & EV_READ) +\& /* stdin might have data for us, joy! */; +\& else if (revents & EV_TIMER) +\& /* doh, nothing entered */; +\& } +\& +\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); +.Ve +.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 +.IX Item "ev_feed_fd_event (loop, int fd, int revents)" +Feed an event on the given fd, as if a file descriptor backend detected +the given events. +.IP "ev_feed_signal_event (loop, int signum)" 4 +.IX Item "ev_feed_signal_event (loop, int signum)" +Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR, +which is async-safe. +.SH "COMMON OR USEFUL IDIOMS (OR BOTH)" +.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)" +This section explains some common idioms that are not immediately +obvious. Note that examples are sprinkled over the whole manual, and this +section only contains stuff that wouldn't fit anywhere else. +.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0" +.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" +Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read +or modify at any time: libev will completely ignore it. This can be used +to associate arbitrary data with your watcher. If you need more data and +don't want to allocate memory separately and store a pointer to it in that +data member, you can also \*(L"subclass\*(R" the watcher type and provide your own +data: +.PP +.Vb 7 +\& struct my_io +\& { +\& ev_io io; +\& int otherfd; +\& void *somedata; +\& struct whatever *mostinteresting; +\& }; +\& +\& ... +\& struct my_io w; +\& ev_io_init (&w.io, my_cb, fd, EV_READ); +.Ve +.PP +And since your callback will be called with a pointer to the watcher, you +can cast it back to your own type: +.PP +.Vb 5 +\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) +\& { +\& struct my_io *w = (struct my_io *)w_; +\& ... +\& } +.Ve +.PP +More interesting and less C\-conformant ways of casting your callback +function type instead have been omitted. +.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0" +.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS" +Another common scenario is to use some data structure with multiple +embedded watchers, in effect creating your own watcher that combines +multiple libev event sources into one \*(L"super-watcher\*(R": +.PP +.Vb 6 +\& struct my_biggy +\& { +\& int some_data; +\& ev_timer t1; +\& ev_timer t2; +\& } +.Ve +.PP +In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more +complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in +the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need +to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for +real programmers): +.PP +.Vb 1 +\& #include <stddef.h> +\& +\& static void +\& t1_cb (EV_P_ ev_timer *w, int revents) +\& { +\& struct my_biggy big = (struct my_biggy *) +\& (((char *)w) \- offsetof (struct my_biggy, t1)); +\& } +\& +\& static void +\& t2_cb (EV_P_ ev_timer *w, int revents) +\& { +\& struct my_biggy big = (struct my_biggy *) +\& (((char *)w) \- offsetof (struct my_biggy, t2)); +\& } +.Ve +.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0" +.IX Subsection "AVOIDING FINISHING BEFORE RETURNING" +Often you have structures like this in event-based programs: +.PP +.Vb 4 +\& callback () +\& { +\& free (request); +\& } +\& +\& request = start_new_request (..., callback); +.Ve +.PP +The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be +used to cancel the operation, or do other things with it. +.PP +It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that +immediately invoke the callback, for example, to report errors. Or you add +some caching layer that finds that it can skip the lengthy aspects of the +operation and simply invoke the callback with the result. +.PP +The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR +has returned, so \f(CW\*(C`request\*(C'\fR is not set. +.PP +Even if you pass the request by some safer means to the callback, you +might want to do something to the request after starting it, such as +canceling it, which probably isn't working so well when the callback has +already been invoked. +.PP +A common way around all these issues is to make sure that +\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If +\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially +delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for +example, or more sneakily, by reusing an existing (stopped) watcher and +pushing it into the pending queue: +.PP +.Vb 2 +\& ev_set_cb (watcher, callback); +\& ev_feed_event (EV_A_ watcher, 0); +.Ve +.PP +This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is +invoked, while not delaying callback invocation too much. +.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0" +.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS" +Often (especially in \s-1GUI\s0 toolkits) there are places where you have +\&\fImodal\fR interaction, which is most easily implemented by recursively +invoking \f(CW\*(C`ev_run\*(C'\fR. +.PP +This brings the problem of exiting \- a callback might want to finish the +main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but +a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one +and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some +other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work. +.PP +The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR +invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is +triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR: +.PP +.Vb 2 +\& // main loop +\& int exit_main_loop = 0; +\& +\& while (!exit_main_loop) +\& ev_run (EV_DEFAULT_ EVRUN_ONCE); +\& +\& // in a modal watcher +\& int exit_nested_loop = 0; +\& +\& while (!exit_nested_loop) +\& ev_run (EV_A_ EVRUN_ONCE); +.Ve +.PP +To exit from any of these loops, just set the corresponding exit variable: +.PP +.Vb 2 +\& // exit modal loop +\& exit_nested_loop = 1; +\& +\& // exit main program, after modal loop is finished +\& exit_main_loop = 1; +\& +\& // exit both +\& exit_main_loop = exit_nested_loop = 1; +.Ve +.SS "\s-1THREAD LOCKING EXAMPLE\s0" +.IX Subsection "THREAD LOCKING EXAMPLE" +Here is a fictitious example of how to run an event loop in a different +thread from where callbacks are being invoked and watchers are +created/added/removed. +.PP +For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module, +which uses exactly this technique (which is suited for many high-level +languages). +.PP +The example uses a pthread mutex to protect the loop data, a condition +variable to wait for callback invocations, an async watcher to notify the +event loop thread and an unspecified mechanism to wake up the main thread. +.PP +First, you need to associate some data with the event loop: +.PP +.Vb 6 +\& typedef struct { +\& mutex_t lock; /* global loop lock */ +\& ev_async async_w; +\& thread_t tid; +\& cond_t invoke_cv; +\& } userdata; +\& +\& void prepare_loop (EV_P) +\& { +\& // for simplicity, we use a static userdata struct. +\& static userdata u; +\& +\& ev_async_init (&u\->async_w, async_cb); +\& ev_async_start (EV_A_ &u\->async_w); +\& +\& pthread_mutex_init (&u\->lock, 0); +\& pthread_cond_init (&u\->invoke_cv, 0); +\& +\& // now associate this with the loop +\& ev_set_userdata (EV_A_ u); +\& ev_set_invoke_pending_cb (EV_A_ l_invoke); +\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire); +\& +\& // then create the thread running ev_run +\& pthread_create (&u\->tid, 0, l_run, EV_A); +\& } +.Ve +.PP +The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used +solely to wake up the event loop so it takes notice of any new watchers +that might have been added: +.PP +.Vb 5 +\& static void +\& async_cb (EV_P_ ev_async *w, int revents) +\& { +\& // just used for the side effects +\& } +.Ve +.PP +The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex +protecting the loop data, respectively. +.PP +.Vb 6 +\& static void +\& l_release (EV_P) +\& { +\& userdata *u = ev_userdata (EV_A); +\& pthread_mutex_unlock (&u\->lock); +\& } +\& +\& static void +\& l_acquire (EV_P) +\& { +\& userdata *u = ev_userdata (EV_A); +\& pthread_mutex_lock (&u\->lock); +\& } +.Ve +.PP +The event loop thread first acquires the mutex, and then jumps straight +into \f(CW\*(C`ev_run\*(C'\fR: +.PP +.Vb 4 +\& void * +\& l_run (void *thr_arg) +\& { +\& struct ev_loop *loop = (struct ev_loop *)thr_arg; +\& +\& l_acquire (EV_A); +\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0); +\& ev_run (EV_A_ 0); +\& l_release (EV_A); +\& +\& return 0; +\& } +.Ve +.PP +Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will +signal the main thread via some unspecified mechanism (signals? pipe +writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers +have been called (in a while loop because a) spurious wakeups are possible +and b) skipping inter-thread-communication when there are no pending +watchers is very beneficial): +.PP +.Vb 4 +\& static void +\& l_invoke (EV_P) +\& { +\& userdata *u = ev_userdata (EV_A); +\& +\& while (ev_pending_count (EV_A)) +\& { +\& wake_up_other_thread_in_some_magic_or_not_so_magic_way (); +\& pthread_cond_wait (&u\->invoke_cv, &u\->lock); +\& } +\& } +.Ve +.PP +Now, whenever the main thread gets told to invoke pending watchers, it +will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop +thread to continue: +.PP +.Vb 4 +\& static void +\& real_invoke_pending (EV_P) +\& { +\& userdata *u = ev_userdata (EV_A); +\& +\& pthread_mutex_lock (&u\->lock); +\& ev_invoke_pending (EV_A); +\& pthread_cond_signal (&u\->invoke_cv); +\& pthread_mutex_unlock (&u\->lock); +\& } +.Ve +.PP +Whenever you want to start/stop a watcher or do other modifications to an +event loop, you will now have to lock: +.PP +.Vb 2 +\& ev_timer timeout_watcher; +\& userdata *u = ev_userdata (EV_A); +\& +\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); +\& +\& pthread_mutex_lock (&u\->lock); +\& ev_timer_start (EV_A_ &timeout_watcher); +\& ev_async_send (EV_A_ &u\->async_w); +\& pthread_mutex_unlock (&u\->lock); +.Ve +.PP +Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise +an event loop currently blocking in the kernel will have no knowledge +about the newly added timer. By waking up the loop it will pick up any new +watchers in the next event loop iteration. +.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0" +.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS" +While the overhead of a callback that e.g. schedules a thread is small, it +is still an overhead. If you embed libev, and your main usage is with some +kind of threads or coroutines, you might want to customise libev so that +doesn't need callbacks anymore. +.PP +Imagine you have coroutines that you can switch to using a function +\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR +and that due to some magic, the currently active coroutine is stored in a +global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev +event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note +the differing \f(CW\*(C`;\*(C'\fR conventions): +.PP +.Vb 2 +\& #define EV_CB_DECLARE(type) struct my_coro *cb; +\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb) +.Ve +.PP +That means instead of having a C callback function, you store the +coroutine to switch to in each watcher, and instead of having libev call +your callback, you instead have it switch to that coroutine. +.PP +A coroutine might now wait for an event with a function called +\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't +matter when, or whether the watcher is active or not when this function is +called): +.PP +.Vb 6 +\& void +\& wait_for_event (ev_watcher *w) +\& { +\& ev_set_cb (w, current_coro); +\& switch_to (libev_coro); +\& } +.Ve +.PP +That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and +continues the libev coroutine, which, when appropriate, switches back to +this or any other coroutine. +.PP +You can do similar tricks if you have, say, threads with an event queue \- +instead of storing a coroutine, you store the queue object and instead of +switching to a coroutine, you push the watcher onto the queue and notify +any waiters. +.PP +To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two +files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files: +.PP +.Vb 4 +\& // my_ev.h +\& #define EV_CB_DECLARE(type) struct my_coro *cb; +\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb) +\& #include "../libev/ev.h" +\& +\& // my_ev.c +\& #define EV_H "my_ev.h" +\& #include "../libev/ev.c" +.Ve +.PP +And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile +\&\fImy_ev.c\fR into your project. When properly specifying include paths, you +can even use \fIev.h\fR as header file name directly. +.SH "LIBEVENT EMULATION" +.IX Header "LIBEVENT EMULATION" +Libev offers a compatibility emulation layer for libevent. It cannot +emulate the internals of libevent, so here are some usage hints: +.IP "\(bu" 4 +Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated. +.Sp +This was the newest libevent version available when libev was implemented, +and is still mostly unchanged in 2010. +.IP "\(bu" 4 +Use it by including <event.h>, as usual. +.IP "\(bu" 4 +The following members are fully supported: ev_base, ev_callback, +ev_arg, ev_fd, ev_res, ev_events. +.IP "\(bu" 4 +Avoid using ev_flags and the EVLIST_*\-macros, while it is +maintained by libev, it does not work exactly the same way as in libevent (consider +it a private \s-1API\s0). +.IP "\(bu" 4 +Priorities are not currently supported. Initialising priorities +will fail and all watchers will have the same priority, even though there +is an ev_pri field. +.IP "\(bu" 4 +In libevent, the last base created gets the signals, in libev, the +base that registered the signal gets the signals. +.IP "\(bu" 4 +Other members are not supported. +.IP "\(bu" 4 +The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need +to use the libev header file and library. +.SH "\*(C+ SUPPORT" +.IX Header " SUPPORT" +.SS "C \s-1API\s0" +.IX Subsection "C API" +The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the +libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0 +will work fine. +.PP +Proper exception specifications might have to be added to callbacks passed +to libev: exceptions may be thrown only from watcher callbacks, all other +callbacks (allocator, syserr, loop acquire/release and periodic reschedule +callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR +specification. If you have code that needs to be compiled as both C and +\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this: +.PP +.Vb 6 +\& static void +\& fatal_error (const char *msg) EV_NOEXCEPT +\& { +\& perror (msg); +\& abort (); +\& } +\& +\& ... +\& ev_set_syserr_cb (fatal_error); +.Ve +.PP +The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR, +\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter +because it runs cleanup watchers). +.PP +Throwing exceptions in watcher callbacks is only supported if libev itself +is compiled with a \*(C+ compiler or your C and \*(C+ environments allow +throwing exceptions through C libraries (most do). +.SS "\*(C+ \s-1API\s0" +.IX Subsection " API" +Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow +you to use some convenience methods to start/stop watchers and also change +the callback model to a model using method callbacks on objects. +.PP +To use it, +.PP +.Vb 1 +\& #include <ev++.h> +.Ve +.PP +This automatically includes \fIev.h\fR and puts all of its definitions (many +of them macros) into the global namespace. All \*(C+ specific things are +put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding +options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. +.PP +Care has been taken to keep the overhead low. The only data member the \*(C+ +classes add (compared to plain C\-style watchers) is the event loop pointer +that the watcher is associated with (or no additional members at all if +you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). +.PP +Currently, functions, static and non-static member functions and classes +with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy +to add as long as they only need one additional pointer for context. If +you need support for other types of functors please contact the author +(preferably after implementing it). +.PP +For all this to work, your \*(C+ compiler either has to use the same calling +conventions as your C compiler (for static member functions), or you have +to embed libev and compile libev itself as \*(C+. +.PP +Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: +.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4 +.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 +.IX Item "ev::READ, ev::WRITE etc." +These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. +macros from \fIev.h\fR. +.ie n .IP """ev::tstamp"", ""ev::now""" 4 +.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 +.IX Item "ev::tstamp, ev::now" +Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. +.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4 +.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 +.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." +For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of +the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR +which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro +defined by many implementations. +.Sp +All of those classes have these methods: +.RS 4 +.IP "ev::TYPE::TYPE ()" 4 +.IX Item "ev::TYPE::TYPE ()" +.PD 0 +.IP "ev::TYPE::TYPE (loop)" 4 +.IX Item "ev::TYPE::TYPE (loop)" +.IP "ev::TYPE::~TYPE" 4 +.IX Item "ev::TYPE::~TYPE" +.PD +The constructor (optionally) takes an event loop to associate the watcher +with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. +.Sp +The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the +\&\f(CW\*(C`set\*(C'\fR method before starting it. +.Sp +It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR +method to set a callback before you can start the watcher. +.Sp +(The reason why you have to use a method is a limitation in \*(C+ which does +not allow explicit template arguments for constructors). +.Sp +The destructor automatically stops the watcher if it is active. +.IP "w\->set<class, &class::method> (object *)" 4 +.IX Item "w->set<class, &class::method> (object *)" +This method sets the callback method to call. The method has to have a +signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as +first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as +parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher. +.Sp +This method synthesizes efficient thunking code to call your method from +the C callback that libev requires. If your compiler can inline your +callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and +your compiler is good :), then the method will be fully inlined into the +thunking function, making it as fast as a direct C callback. +.Sp +Example: simple class declaration and watcher initialisation +.Sp +.Vb 4 +\& struct myclass +\& { +\& void io_cb (ev::io &w, int revents) { } +\& } +\& +\& myclass obj; +\& ev::io iow; +\& iow.set <myclass, &myclass::io_cb> (&obj); +.Ve +.IP "w\->set (object *)" 4 +.IX Item "w->set (object *)" +This is a variation of a method callback \- leaving out the method to call +will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use +functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all +the time. Incidentally, you can then also leave out the template argument +list. +.Sp +The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w, +int revents)\*(C'\fR. +.Sp +See the method\-\f(CW\*(C`set\*(C'\fR above for more details. +.Sp +Example: use a functor object as callback. +.Sp +.Vb 7 +\& struct myfunctor +\& { +\& void operator() (ev::io &w, int revents) +\& { +\& ... +\& } +\& } +\& +\& myfunctor f; +\& +\& ev::io w; +\& w.set (&f); +.Ve +.IP "w\->set<function> (void *data = 0)" 4 +.IX Item "w->set<function> (void *data = 0)" +Also sets a callback, but uses a static method or plain function as +callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's +\&\f(CW\*(C`data\*(C'\fR member and is free for you to use. +.Sp +The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. +.Sp +See the method\-\f(CW\*(C`set\*(C'\fR above for more details. +.Sp +Example: Use a plain function as callback. +.Sp +.Vb 2 +\& static void io_cb (ev::io &w, int revents) { } +\& iow.set <io_cb> (); +.Ve +.IP "w\->set (loop)" 4 +.IX Item "w->set (loop)" +Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only +do this when the watcher is inactive (and not pending either). +.IP "w\->set ([arguments])" 4 +.IX Item "w->set ([arguments])" +Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>), +with the same arguments. Either this method or a suitable start method +must be called at least once. Unlike the C counterpart, an active watcher +gets automatically stopped and restarted when reconfiguring it with this +method. +.Sp +For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid +clashing with the \f(CW\*(C`set (loop)\*(C'\fR method. +.Sp +For \f(CW\*(C`ev::io\*(C'\fR watchers there is an additional \f(CW\*(C`set\*(C'\fR method that acepts a +new event mask only, and internally calls \f(CW\*(C`ev_io_modfify\*(C'\fR. +.IP "w\->start ()" 4 +.IX Item "w->start ()" +Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the +constructor already stores the event loop. +.IP "w\->start ([arguments])" 4 +.IX Item "w->start ([arguments])" +Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often +convenient to wrap them in one call. Uses the same type of arguments as +the configure \f(CW\*(C`set\*(C'\fR method of the watcher. +.IP "w\->stop ()" 4 +.IX Item "w->stop ()" +Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. +.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4 +.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4 +.IX Item "w->again () (ev::timer, ev::periodic only)" +For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding +\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. +.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 +.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4 +.IX Item "w->sweep () (ev::embed only)" +Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. +.ie n .IP "w\->update () (""ev::stat"" only)" 4 +.el .IP "w\->update () (\f(CWev::stat\fR only)" 4 +.IX Item "w->update () (ev::stat only)" +Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. +.RE +.RS 4 +.RE +.PP +Example: Define a class with two I/O and idle watchers, start the I/O +watchers in the constructor. +.PP +.Vb 5 +\& class myclass +\& { +\& ev::io io ; void io_cb (ev::io &w, int revents); +\& ev::io io2 ; void io2_cb (ev::io &w, int revents); +\& ev::idle idle; void idle_cb (ev::idle &w, int revents); +\& +\& myclass (int fd) +\& { +\& io .set <myclass, &myclass::io_cb > (this); +\& io2 .set <myclass, &myclass::io2_cb > (this); +\& idle.set <myclass, &myclass::idle_cb> (this); +\& +\& io.set (fd, ev::WRITE); // configure the watcher +\& io.start (); // start it whenever convenient +\& +\& io2.start (fd, ev::READ); // set + start in one call +\& } +\& }; +.Ve +.SH "OTHER LANGUAGE BINDINGS" +.IX Header "OTHER LANGUAGE BINDINGS" +Libev does not offer other language bindings itself, but bindings for a +number of languages exist in the form of third-party packages. If you know +any interesting language binding in addition to the ones listed here, drop +me a note. +.IP "Perl" 4 +.IX Item "Perl" +The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test +libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module, +there are additional modules that implement libev-compatible interfaces +to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays), +\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR +and \f(CW\*(C`EV::Glib\*(C'\fR). +.Sp +It can be found and installed via \s-1CPAN,\s0 its homepage is at +<http://software.schmorp.de/pkg/EV>. +.IP "Python" 4 +.IX Item "Python" +Python bindings can be found at <http://code.google.com/p/pyev/>. It +seems to be quite complete and well-documented. +.IP "Ruby" 4 +.IX Item "Ruby" +Tony Arcieri has written a ruby extension that offers access to a subset +of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and +more on top of it. It can be found via gem servers. Its homepage is at +<http://rev.rubyforge.org/>. +.Sp +Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR +makes rev work even on mingw. +.IP "Haskell" 4 +.IX Item "Haskell" +A haskell binding to libev is available at +<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>. +.IP "D" 4 +.IX Item "D" +Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to +be found at <http://www.llucax.com.ar/proj/ev.d/index.html>. +.IP "Ocaml" 4 +.IX Item "Ocaml" +Erkki Seppala has written Ocaml bindings for libev, to be found at +<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>. +.IP "Lua" 4 +.IX Item "Lua" +Brian Maher has written a partial interface to libev for lua (at the +time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at +<http://github.com/brimworks/lua\-ev>. +.IP "Javascript" 4 +.IX Item "Javascript" +Node.js (<http://nodejs.org>) uses libev as the underlying event library. +.IP "Others" 4 +.IX Item "Others" +There are others, and I stopped counting. +.SH "MACRO MAGIC" +.IX Header "MACRO MAGIC" +Libev can be compiled with a variety of options, the most fundamental +of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) +functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. +.PP +To make it easier to write programs that cope with either variant, the +following macros are defined: +.ie n .IP """EV_A"", ""EV_A_""" 4 +.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 +.IX Item "EV_A, EV_A_" +This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev +loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, +\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: +.Sp +.Vb 3 +\& ev_unref (EV_A); +\& ev_timer_add (EV_A_ watcher); +\& ev_run (EV_A_ 0); +.Ve +.Sp +It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, +which is often provided by the following macro. +.ie n .IP """EV_P"", ""EV_P_""" 4 +.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 +.IX Item "EV_P, EV_P_" +This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev +loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, +\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: +.Sp +.Vb 2 +\& // this is how ev_unref is being declared +\& static void ev_unref (EV_P); +\& +\& // this is how you can declare your typical callback +\& static void cb (EV_P_ ev_timer *w, int revents) +.Ve +.Sp +It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite +suitable for use with \f(CW\*(C`EV_A\*(C'\fR. +.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4 +.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 +.IX Item "EV_DEFAULT, EV_DEFAULT_" +Similar to the other two macros, this gives you the value of the default +loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop +will be initialised if it isn't already initialised. +.Sp +For non-multiplicity builds, these macros do nothing, so you always have +to initialise the loop somewhere. +.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4 +.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4 +.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_" +Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the +default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour +is undefined when the default loop has not been initialised by a previous +execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR. +.Sp +It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first +watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards. +.PP +Example: Declare and initialise a check watcher, utilising the above +macros so it will work regardless of whether multiple loops are supported +or not. +.PP +.Vb 5 +\& static void +\& check_cb (EV_P_ ev_timer *w, int revents) +\& { +\& ev_check_stop (EV_A_ w); +\& } +\& +\& ev_check check; +\& ev_check_init (&check, check_cb); +\& ev_check_start (EV_DEFAULT_ &check); +\& ev_run (EV_DEFAULT_ 0); +.Ve +.SH "EMBEDDING" +.IX Header "EMBEDDING" +Libev can (and often is) directly embedded into host +applications. Examples of applications that embed it include the Deliantra +Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) +and rxvt-unicode. +.PP +The goal is to enable you to just copy the necessary files into your +source directory without having to change even a single line in them, so +you can easily upgrade by simply copying (or having a checked-out copy of +libev somewhere in your source tree). +.SS "\s-1FILESETS\s0" +.IX Subsection "FILESETS" +Depending on what features you need you need to include one or more sets of files +in your application. +.PP +\fI\s-1CORE EVENT LOOP\s0\fR +.IX Subsection "CORE EVENT LOOP" +.PP +To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual +configuration (no autoconf): +.PP +.Vb 2 +\& #define EV_STANDALONE 1 +\& #include "ev.c" +.Ve +.PP +This will automatically include \fIev.h\fR, too, and should be done in a +single C source file only to provide the function implementations. To use +it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best +done by writing a wrapper around \fIev.h\fR that you can include instead and +where you can put other configuration options): +.PP +.Vb 2 +\& #define EV_STANDALONE 1 +\& #include "ev.h" +.Ve +.PP +Both header files and implementation files can be compiled with a \*(C+ +compiler (at least, that's a stated goal, and breakage will be treated +as a bug). +.PP +You need the following files in your source tree, or in a directory +in your include path (e.g. in libev/ when using \-Ilibev): +.PP +.Vb 4 +\& ev.h +\& ev.c +\& ev_vars.h +\& ev_wrap.h +\& +\& ev_win32.c required on win32 platforms only +\& +\& ev_select.c only when select backend is enabled +\& ev_poll.c only when poll backend is enabled +\& ev_epoll.c only when the epoll backend is enabled +\& ev_linuxaio.c only when the linux aio backend is enabled +\& ev_iouring.c only when the linux io_uring backend is enabled +\& ev_kqueue.c only when the kqueue backend is enabled +\& ev_port.c only when the solaris port backend is enabled +.Ve +.PP +\&\fIev.c\fR includes the backend files directly when enabled, so you only need +to compile this single file. +.PP +\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR +.IX Subsection "LIBEVENT COMPATIBILITY API" +.PP +To include the libevent compatibility \s-1API,\s0 also include: +.PP +.Vb 1 +\& #include "event.c" +.Ve +.PP +in the file including \fIev.c\fR, and: +.PP +.Vb 1 +\& #include "event.h" +.Ve +.PP +in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR. +.PP +You need the following additional files for this: +.PP +.Vb 2 +\& event.h +\& event.c +.Ve +.PP +\fI\s-1AUTOCONF SUPPORT\s0\fR +.IX Subsection "AUTOCONF SUPPORT" +.PP +Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in +whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your +\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then +include \fIconfig.h\fR and configure itself accordingly. +.PP +For this of course you need the m4 file: +.PP +.Vb 1 +\& libev.m4 +.Ve +.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0" +.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" +Libev can be configured via a variety of preprocessor symbols you have to +define before including (or compiling) any of its files. The default in +the absence of autoconf is documented for every option. +.PP +Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different +values when compiling libev vs. including \fIev.h\fR, so it is permissible +to redefine them before including \fIev.h\fR without breaking compatibility +to a compiled library. All other symbols change the \s-1ABI,\s0 which means all +users of libev and the libev code itself must be compiled with compatible +settings. +.IP "\s-1EV_COMPAT3\s0 (h)" 4 +.IX Item "EV_COMPAT3 (h)" +Backwards compatibility is a major concern for libev. This is why this +release of libev comes with wrappers for the functions and symbols that +have been renamed between libev version 3 and 4. +.Sp +You can disable these wrappers (to test compatibility with future +versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your +sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR +from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR +typedef in that case. +.Sp +In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR, +and in some even more future version the compatibility code will be +removed completely. +.IP "\s-1EV_STANDALONE\s0 (h)" 4 +.IX Item "EV_STANDALONE (h)" +Must always be \f(CW1\fR if you do not use autoconf configuration, which +keeps libev from including \fIconfig.h\fR, and it also defines dummy +implementations for some libevent functions (such as logging, which is not +supported). It will also not define any of the structs usually found in +\&\fIevent.h\fR that are not directly supported by the libev core alone. +.Sp +In standalone mode, libev will still try to automatically deduce the +configuration, but has to be more conservative. +.IP "\s-1EV_USE_FLOOR\s0" 4 +.IX Item "EV_USE_FLOOR" +If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its +periodic reschedule calculations, otherwise libev will fall back on a +portable (slower) implementation. If you enable this, you usually have to +link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR +function is not available will fail, so the safe default is to not enable +this. +.IP "\s-1EV_USE_MONOTONIC\s0" 4 +.IX Item "EV_USE_MONOTONIC" +If defined to be \f(CW1\fR, libev will try to detect the availability of the +monotonic clock option at both compile time and runtime. Otherwise no +use of the monotonic clock option will be attempted. If you enable this, +you usually have to link against librt or something similar. Enabling it +when the functionality isn't available is safe, though, although you have +to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR +function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR. +.IP "\s-1EV_USE_REALTIME\s0" 4 +.IX Item "EV_USE_REALTIME" +If defined to be \f(CW1\fR, libev will try to detect the availability of the +real-time clock option at compile time (and assume its availability +at runtime if successful). Otherwise no use of the real-time clock +option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR +by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect +correctness. See the note about libraries in the description of +\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of +\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR. +.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4 +.IX Item "EV_USE_CLOCK_SYSCALL" +If defined to be \f(CW1\fR, libev will try to use a direct syscall instead +of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option +exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR +unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded +programs needlessly. Using a direct syscall is slightly slower (in +theory), because no optimised vdso implementation can be used, but avoids +the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or +higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR). +.IP "\s-1EV_USE_NANOSLEEP\s0" 4 +.IX Item "EV_USE_NANOSLEEP" +If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available +and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR. +.IP "\s-1EV_USE_EVENTFD\s0" 4 +.IX Item "EV_USE_EVENTFD" +If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is +available and will probe for kernel support at runtime. This will improve +\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption. +If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc +2.7 or newer, otherwise disabled. +.IP "\s-1EV_USE_SIGNALFD\s0" 4 +.IX Item "EV_USE_SIGNALFD" +If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is +available and will probe for kernel support at runtime. This enables +the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If +undefined, it will be enabled if the headers indicate GNU/Linux + Glibc +2.7 or newer, otherwise disabled. +.IP "\s-1EV_USE_TIMERFD\s0" 4 +.IX Item "EV_USE_TIMERFD" +If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is +available and will probe for kernel support at runtime. This allows +libev to detect time jumps accurately. If undefined, it will be enabled +if the headers indicate GNU/Linux + Glibc 2.8 or newer and define +\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled. +.IP "\s-1EV_USE_EVENTFD\s0" 4 +.IX Item "EV_USE_EVENTFD" +If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is +available and will probe for kernel support at runtime. This will improve +\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption. +If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc +2.7 or newer, otherwise disabled. +.IP "\s-1EV_USE_SELECT\s0" 4 +.IX Item "EV_USE_SELECT" +If undefined or defined to be \f(CW1\fR, libev will compile in support for the +\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no +other method takes over, select will be it. Otherwise the select backend +will not be compiled in. +.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 +.IX Item "EV_SELECT_USE_FD_SET" +If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR +structure. This is useful if libev doesn't compile due to a missing +\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout +on exotic systems. This usually limits the range of file descriptors to +some low limit such as 1024 or might have other limitations (winsocket +only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, +configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR. +.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 +.IX Item "EV_SELECT_IS_WINSOCKET" +When defined to \f(CW1\fR, the select backend will assume that +select/socket/connect etc. don't understand file descriptors but +wants osf handles on win32 (this is the case when the select to +be used is the winsock select). This means that it will call +\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, +it is assumed that all these functions actually work on fds, even +on win32. Should not be defined on non\-win32 platforms. +.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4 +.IX Item "EV_FD_TO_WIN32_HANDLE(fd)" +If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map +file descriptors to socket handles. When not defining this symbol (the +default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually +correct. In some cases, programs use their own file descriptor management, +in which case they can provide this function to map fds to socket handles. +.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4 +.IX Item "EV_WIN32_HANDLE_TO_FD(handle)" +If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors +using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing +their own fd to handle mapping, overwriting this function makes it easier +to do so. This can be done by defining this macro to an appropriate value. +.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4 +.IX Item "EV_WIN32_CLOSE_FD(fd)" +If programs implement their own fd to handle mapping on win32, then this +macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister +file descriptors again. Note that the replacement function has to close +the underlying \s-1OS\s0 handle. +.IP "\s-1EV_USE_WSASOCKET\s0" 4 +.IX Item "EV_USE_WSASOCKET" +If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal +communication socket, which works better in some environments. Otherwise, +the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other +environments. +.IP "\s-1EV_USE_POLL\s0" 4 +.IX Item "EV_USE_POLL" +If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) +backend. Otherwise it will be enabled on non\-win32 platforms. It +takes precedence over select. +.IP "\s-1EV_USE_EPOLL\s0" 4 +.IX Item "EV_USE_EPOLL" +If defined to be \f(CW1\fR, libev will compile in support for the Linux +\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for GNU/Linux systems. If undefined, it will be enabled if the +headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. +.IP "\s-1EV_USE_LINUXAIO\s0" 4 +.IX Item "EV_USE_LINUXAIO" +If defined to be \f(CW1\fR, libev will compile in support for the Linux aio +backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be +enabled on linux, otherwise disabled. +.IP "\s-1EV_USE_IOURING\s0" 4 +.IX Item "EV_USE_IOURING" +If defined to be \f(CW1\fR, libev will compile in support for the Linux +io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's +current limitations it has to be requested explicitly. If undefined, it +will be enabled on linux, otherwise disabled. +.IP "\s-1EV_USE_KQUEUE\s0" 4 +.IX Item "EV_USE_KQUEUE" +If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style +\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only +supports some types of fds correctly (the only platform we found that +supports ptys for example was NetBSD), so kqueue might be compiled in, but +not be used unless explicitly requested. The best way to use it is to find +out whether kqueue supports your type of fd properly and use an embedded +kqueue loop. +.IP "\s-1EV_USE_PORT\s0" 4 +.IX Item "EV_USE_PORT" +If defined to be \f(CW1\fR, libev will compile in support for the Solaris +10 port style backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for Solaris 10 systems. +.IP "\s-1EV_USE_DEVPOLL\s0" 4 +.IX Item "EV_USE_DEVPOLL" +Reserved for future expansion, works like the \s-1USE\s0 symbols above. +.IP "\s-1EV_USE_INOTIFY\s0" 4 +.IX Item "EV_USE_INOTIFY" +If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify +interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will +be detected at runtime. If undefined, it will be enabled if the headers +indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. +.IP "\s-1EV_NO_SMP\s0" 4 +.IX Item "EV_NO_SMP" +If defined to be \f(CW1\fR, libev will assume that memory is always coherent +between threads, that is, threads can be used, but threads never run on +different cpus (or different cpu cores). This reduces dependencies +and makes libev faster. +.IP "\s-1EV_NO_THREADS\s0" 4 +.IX Item "EV_NO_THREADS" +If defined to be \f(CW1\fR, libev will assume that it will never be called from +different threads (that includes signal handlers), which is a stronger +assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes +libev faster. +.IP "\s-1EV_ATOMIC_T\s0" 4 +.IX Item "EV_ATOMIC_T" +Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose +access is atomic with respect to other threads or signal contexts. No +such type is easily found in the C language, so you can provide your own +type that you know is safe for your purposes. It is used both for signal +handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR +watchers. +.Sp +In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR +(from \fIsignal.h\fR), which is usually good enough on most platforms. +.IP "\s-1EV_H\s0 (h)" 4 +.IX Item "EV_H (h)" +The name of the \fIev.h\fR header file used to include it. The default if +undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be +used to virtually rename the \fIev.h\fR header file in case of conflicts. +.IP "\s-1EV_CONFIG_H\s0 (h)" 4 +.IX Item "EV_CONFIG_H (h)" +If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override +\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to +\&\f(CW\*(C`EV_H\*(C'\fR, above. +.IP "\s-1EV_EVENT_H\s0 (h)" 4 +.IX Item "EV_EVENT_H (h)" +Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea +of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR. +.IP "\s-1EV_PROTOTYPES\s0 (h)" 4 +.IX Item "EV_PROTOTYPES (h)" +If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function +prototypes, but still define all the structs and other symbols. This is +occasionally useful if you want to provide your own wrapper functions +around libev functions. +.IP "\s-1EV_MULTIPLICITY\s0" 4 +.IX Item "EV_MULTIPLICITY" +If undefined or defined to \f(CW1\fR, then all event-loop-specific functions +will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create +additional independent event loops. Otherwise there will be no support +for multiple event loops and there is no first event loop pointer +argument. Instead, all functions act on the single default loop. +.Sp +Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a +default loop when multiplicity is switched off \- you always have to +initialise the loop manually in this case. +.IP "\s-1EV_MINPRI\s0" 4 +.IX Item "EV_MINPRI" +.PD 0 +.IP "\s-1EV_MAXPRI\s0" 4 +.IX Item "EV_MAXPRI" +.PD +The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to +\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can +provide for more priorities by overriding those symbols (usually defined +to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively). +.Sp +When doing priority-based operations, libev usually has to linearly search +all the priorities, so having many of them (hundreds) uses a lot of space +and time, so using the defaults of five priorities (\-2 .. +2) is usually +fine. +.Sp +If your embedding application does not need any priorities, defining these +both to \f(CW0\fR will save some memory and \s-1CPU.\s0 +.IP "\s-1EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE.\s0" 4 +.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE." +If undefined or defined to be \f(CW1\fR (and the platform supports it), then +the respective watcher type is supported. If defined to be \f(CW0\fR, then it +is not. Disabling watcher types mainly saves code size. +.IP "\s-1EV_FEATURES\s0" 4 +.IX Item "EV_FEATURES" +If you need to shave off some kilobytes of code at the expense of some +speed (but with the full \s-1API\s0), you can define this symbol to request +certain subsets of functionality. The default is to enable all features +that can be enabled on the platform. +.Sp +A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset +with some broad features you want) and then selectively re-enable +additional parts you want, for example if you want everything minimal, +but multiple event loop support, async and child watchers and the poll +backend, use this: +.Sp +.Vb 5 +\& #define EV_FEATURES 0 +\& #define EV_MULTIPLICITY 1 +\& #define EV_USE_POLL 1 +\& #define EV_CHILD_ENABLE 1 +\& #define EV_ASYNC_ENABLE 1 +.Ve +.Sp +The actual value is a bitset, it can be a combination of the following +values (by default, all of these are enabled): +.RS 4 +.ie n .IP "1 \- faster/larger code" 4 +.el .IP "\f(CW1\fR \- faster/larger code" 4 +.IX Item "1 - faster/larger code" +Use larger code to speed up some operations. +.Sp +Currently this is used to override some inlining decisions (enlarging the +code size by roughly 30% on amd64). +.Sp +When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with +gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of +assertions. +.Sp +The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler +(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR). +.ie n .IP "2 \- faster/larger data structures" 4 +.el .IP "\f(CW2\fR \- faster/larger data structures" 4 +.IX Item "2 - faster/larger data structures" +Replaces the small 2\-heap for timer management by a faster 4\-heap, larger +hash table sizes and so on. This will usually further increase code size +and can additionally have an effect on the size of data structures at +runtime. +.Sp +The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler +(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR). +.ie n .IP "4 \- full \s-1API\s0 configuration" 4 +.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4 +.IX Item "4 - full API configuration" +This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and +enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1). +.ie n .IP "8 \- full \s-1API\s0" 4 +.el .IP "\f(CW8\fR \- full \s-1API\s0" 4 +.IX Item "8 - full API" +This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for +details on which parts of the \s-1API\s0 are still available without this +feature, and do not complain if this subset changes over time. +.ie n .IP "16 \- enable all optional watcher types" 4 +.el .IP "\f(CW16\fR \- enable all optional watcher types" 4 +.IX Item "16 - enable all optional watcher types" +Enables all optional watcher types. If you want to selectively enable +only some watcher types other than I/O and timers (e.g. prepare, +embed, async, child...) you can enable them manually by defining +\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead. +.ie n .IP "32 \- enable all backends" 4 +.el .IP "\f(CW32\fR \- enable all backends" 4 +.IX Item "32 - enable all backends" +This enables all backends \- without this feature, you need to enable at +least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice). +.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4 +.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4 +.IX Item "64 - enable OS-specific helper APIs" +Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by +default. +.RE +.RS 4 +.Sp +Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR +reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb +code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O +watchers, timers and monotonic clock support. +.Sp +With an intelligent-enough linker (gcc+binutils are intelligent enough +when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by +your program might be left out as well \- a binary starting a timer and an +I/O watcher then might come out at only 5Kb. +.RE +.IP "\s-1EV_API_STATIC\s0" 4 +.IX Item "EV_API_STATIC" +If this symbol is defined (by default it is not), then all identifiers +will have static linkage. This means that libev will not export any +identifiers, and you cannot link against libev anymore. This can be useful +when you embed libev, only want to use libev functions in a single file, +and do not want its identifiers to be visible. +.Sp +To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that +wants to use libev. +.Sp +This option only works when libev is compiled with a C compiler, as \*(C+ +doesn't support the required declaration syntax. +.IP "\s-1EV_AVOID_STDIO\s0" 4 +.IX Item "EV_AVOID_STDIO" +If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio +functions (printf, scanf, perror etc.). This will increase the code size +somewhat, but if your program doesn't otherwise depend on stdio and your +libc allows it, this avoids linking in the stdio library which is quite +big. +.Sp +Note that error messages might become less precise when this option is +enabled. +.IP "\s-1EV_NSIG\s0" 4 +.IX Item "EV_NSIG" +The highest supported signal number, +1 (or, the number of +signals): Normally, libev tries to deduce the maximum number of signals +automatically, but sometimes this fails, in which case it can be +specified. Also, using a lower number than detected (\f(CW32\fR should be +good for about any system in existence) can save some memory, as libev +statically allocates some 12\-24 bytes per signal number. +.IP "\s-1EV_PID_HASHSIZE\s0" 4 +.IX Item "EV_PID_HASHSIZE" +\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by +pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled), +usually more than enough. If you need to manage thousands of children you +might want to increase this value (\fImust\fR be a power of two). +.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 +.IX Item "EV_INOTIFY_HASHSIZE" +\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by +inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR +disabled), usually more than enough. If you need to manage thousands of +\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a +power of two). +.IP "\s-1EV_USE_4HEAP\s0" 4 +.IX Item "EV_USE_4HEAP" +Heaps are not very cache-efficient. To improve the cache-efficiency of the +timer and periodics heaps, libev uses a 4\-heap when this symbol is defined +to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably +faster performance with many (thousands) of watchers. +.Sp +The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it +will be \f(CW0\fR. +.IP "\s-1EV_HEAP_CACHE_AT\s0" 4 +.IX Item "EV_HEAP_CACHE_AT" +Heaps are not very cache-efficient. To improve the cache-efficiency of the +timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within +the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR), +which uses 8\-12 bytes more per watcher and a few hundred bytes more code, +but avoids random read accesses on heap changes. This improves performance +noticeably with many (hundreds) of watchers. +.Sp +The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it +will be \f(CW0\fR. +.IP "\s-1EV_VERIFY\s0" 4 +.IX Item "EV_VERIFY" +Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will +be done: If set to \f(CW0\fR, no internal verification code will be compiled +in. If set to \f(CW1\fR, then verification code will be compiled in, but not +called. If set to \f(CW2\fR, then the internal verification code will be +called once per loop, which can slow down libev. If set to \f(CW3\fR, then the +verification code will be called very frequently, which will slow down +libev considerably. +.Sp +Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you +disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported. +.Sp +The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it +will be \f(CW0\fR. +.IP "\s-1EV_COMMON\s0" 4 +.IX Item "EV_COMMON" +By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining +this macro to something else you can include more and other types of +members. You have to define it each time you include one of the files, +though, and it must be identical each time. +.Sp +For example, the perl \s-1EV\s0 module uses something like this: +.Sp +.Vb 3 +\& #define EV_COMMON \e +\& SV *self; /* contains this struct */ \e +\& SV *cb_sv, *fh /* note no trailing ";" */ +.Ve +.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 +.IX Item "EV_CB_DECLARE (type)" +.PD 0 +.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 +.IX Item "EV_CB_INVOKE (watcher, revents)" +.IP "ev_set_cb (ev, cb)" 4 +.IX Item "ev_set_cb (ev, cb)" +.PD +Can be used to change the callback member declaration in each watcher, +and the way callbacks are invoked and set. Must expand to a struct member +definition and a statement, respectively. See the \fIev.h\fR header file for +their default definitions. One possible use for overriding these is to +avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use +method calls instead of plain function calls in \*(C+. +.SS "\s-1EXPORTED API SYMBOLS\s0" +.IX Subsection "EXPORTED API SYMBOLS" +If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of +exported symbols, you can use the provided \fISymbol.*\fR files which list +all public symbols, one per line: +.PP +.Vb 2 +\& Symbols.ev for libev proper +\& Symbols.event for the libevent emulation +.Ve +.PP +This can also be used to rename all public symbols to avoid clashes with +multiple versions of libev linked together (which is obviously bad in +itself, but sometimes it is inconvenient to avoid this). +.PP +A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to +include before including \fIev.h\fR: +.PP +.Vb 1 +\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h +.Ve +.PP +This would create a file \fIwrap.h\fR which essentially looks like this: +.PP +.Vb 4 +\& #define ev_backend myprefix_ev_backend +\& #define ev_check_start myprefix_ev_check_start +\& #define ev_check_stop myprefix_ev_check_stop +\& ... +.Ve +.SS "\s-1EXAMPLES\s0" +.IX Subsection "EXAMPLES" +For a real-world example of a program the includes libev +verbatim, you can have a look at the \s-1EV\s0 perl module +(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in +the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public +interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file +will be compiled. It is pretty complex because it provides its own header +file. +.PP +The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file +that everybody includes and which overrides some configure choices: +.PP +.Vb 8 +\& #define EV_FEATURES 8 +\& #define EV_USE_SELECT 1 +\& #define EV_PREPARE_ENABLE 1 +\& #define EV_IDLE_ENABLE 1 +\& #define EV_SIGNAL_ENABLE 1 +\& #define EV_CHILD_ENABLE 1 +\& #define EV_USE_STDEXCEPT 0 +\& #define EV_CONFIG_H <config.h> +\& +\& #include "ev++.h" +.Ve +.PP +And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: +.PP +.Vb 2 +\& #include "ev_cpp.h" +\& #include "ev.c" +.Ve +.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT" +.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT" +.SS "\s-1THREADS AND COROUTINES\s0" +.IX Subsection "THREADS AND COROUTINES" +\fI\s-1THREADS\s0\fR +.IX Subsection "THREADS" +.PP +All libev functions are reentrant and thread-safe unless explicitly +documented otherwise, but libev implements no locking itself. This means +that you can use as many loops as you want in parallel, as long as there +are no concurrent calls into any libev function with the same loop +parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter, +of course): libev guarantees that different event loops share no data +structures that need any locking. +.PP +Or to put it differently: calls with different loop parameters can be done +concurrently from multiple threads, calls with the same loop parameter +must be done serially (but can be done from different threads, as long as +only one thread ever is inside a call at any point in time, e.g. by using +a mutex per loop). +.PP +Specifically to support threads (and signal handlers), libev implements +so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of +concurrency on the same event loop, namely waking it up \*(L"from the +outside\*(R". +.PP +If you want to know which design (one loop, locking, or multiple loops +without or something else still) is best for your problem, then I cannot +help you, but here is some generic advice: +.IP "\(bu" 4 +most applications have a main thread: use the default libev loop +in that thread, or create a separate thread running only the default loop. +.Sp +This helps integrating other libraries or software modules that use libev +themselves and don't care/know about threading. +.IP "\(bu" 4 +one loop per thread is usually a good model. +.Sp +Doing this is almost never wrong, sometimes a better-performance model +exists, but it is always a good start. +.IP "\(bu" 4 +other models exist, such as the leader/follower pattern, where one +loop is handed through multiple threads in a kind of round-robin fashion. +.Sp +Choosing a model is hard \- look around, learn, know that usually you can do +better than you currently do :\-) +.IP "\(bu" 4 +often you need to talk to some other thread which blocks in the +event loop. +.Sp +\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely +(or from signal contexts...). +.Sp +An example use would be to communicate signals or other events that only +work in the default loop by registering the signal watcher with the +default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop +watcher callback into the event loop interested in the signal. +.PP +See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0. +.PP +\fI\s-1COROUTINES\s0\fR +.IX Subsection "COROUTINES" +.PP +Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"): +libev fully supports nesting calls to its functions from different +coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two +different coroutines, and switch freely between both coroutines running +the loop, as long as you don't confuse yourself). The only exception is +that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks. +.PP +Care has been taken to ensure that libev does not keep local state inside +\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as +they do not call any callbacks. +.SS "\s-1COMPILER WARNINGS\s0" +.IX Subsection "COMPILER WARNINGS" +Depending on your compiler and compiler settings, you might get no or a +lot of warnings when compiling libev code. Some people are apparently +scared by this. +.PP +However, these are unavoidable for many reasons. For one, each compiler +has different warnings, and each user has different tastes regarding +warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when +targeting a specific compiler and compiler-version. +.PP +Another reason is that some compiler warnings require elaborate +workarounds, or other changes to the code that make it less clear and less +maintainable. +.PP +And of course, some compiler warnings are just plain stupid, or simply +wrong (because they don't actually warn about the condition their message +seems to warn about). For example, certain older gcc versions had some +warnings that resulted in an extreme number of false positives. These have +been fixed, but some people still insist on making code warn-free with +such buggy versions. +.PP +While libev is written to generate as few warnings as possible, +\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev +with any compiler warnings enabled unless you are prepared to cope with +them (e.g. by ignoring them). Remember that warnings are just that: +warnings, not errors, or proof of bugs. +.SS "\s-1VALGRIND\s0" +.IX Subsection "VALGRIND" +Valgrind has a special section here because it is a popular tool that is +highly useful. Unfortunately, valgrind reports are very hard to interpret. +.PP +If you think you found a bug (memory leak, uninitialised data access etc.) +in libev, then check twice: If valgrind reports something like: +.PP +.Vb 3 +\& ==2274== definitely lost: 0 bytes in 0 blocks. +\& ==2274== possibly lost: 0 bytes in 0 blocks. +\& ==2274== still reachable: 256 bytes in 1 blocks. +.Ve +.PP +Then there is no memory leak, just as memory accounted to global variables +is not a memleak \- the memory is still being referenced, and didn't leak. +.PP +Similarly, under some circumstances, valgrind might report kernel bugs +as if it were a bug in libev (e.g. in realloc or in the poll backend, +although an acceptable workaround has been found here), or it might be +confused. +.PP +Keep in mind that valgrind is a very good tool, but only a tool. Don't +make it into some kind of religion. +.PP +If you are unsure about something, feel free to contact the mailing list +with the full valgrind report and an explanation on why you think this +is a bug in libev (best check the archives, too :). However, don't be +annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance +of learning how to interpret valgrind properly. +.PP +If you need, for some reason, empty reports from valgrind for your project +I suggest using suppression lists. +.SH "PORTABILITY NOTES" +.IX Header "PORTABILITY NOTES" +.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0" +.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS" +GNU/Linux is the only common platform that supports 64 bit file/large file +interfaces but \fIdisables\fR them by default. +.PP +That means that libev compiled in the default environment doesn't support +files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers. +.PP +Unfortunately, many programs try to work around this GNU/Linux issue +by enabling the large file \s-1API,\s0 which makes them incompatible with the +standard libev compiled for their system. +.PP +Likewise, libev cannot enable the large file \s-1API\s0 itself as this would +suddenly make it incompatible to the default compile time environment, +i.e. all programs not using special compile switches. +.SS "\s-1OS/X AND DARWIN BUGS\s0" +.IX Subsection "OS/X AND DARWIN BUGS" +The whole thing is a bug if you ask me \- basically any system interface +you touch is broken, whether it is locales, poll, kqueue or even the +OpenGL drivers. +.PP +\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR +.IX Subsection "kqueue is buggy" +.PP +The kqueue syscall is broken in all known versions \- most versions support +only sockets, many support pipes. +.PP +Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this +rotten platform, but of course you can still ask for it when creating a +loop \- embedding a socket-only kqueue loop into a select-based one is +probably going to work well. +.PP +\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR +.IX Subsection "poll is buggy" +.PP +Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR +implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6 +release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken. +.PP +Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on +this rotten platform, but of course you can still ask for it when creating +a loop. +.PP +\fI\f(CI\*(C`select\*(C'\fI is buggy\fR +.IX Subsection "select is buggy" +.PP +All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this +one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file +descriptors you can pass in to 1024 \- your program suddenly crashes when +you use more. +.PP +There is an undocumented \*(L"workaround\*(R" for this \- defining +\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR +work on \s-1OS/X.\s0 +.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0" +.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS" +\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR +.IX Subsection "errno reentrancy" +.PP +The default compile environment on Solaris is unfortunately so +thread-unsafe that you can't even use components/libraries compiled +without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't +defined by default. A valid, if stupid, implementation choice. +.PP +If you want to use libev in threaded environments you have to make sure +it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined. +.PP +\fIEvent port backend\fR +.IX Subsection "Event port backend" +.PP +The scalable event interface for Solaris is called \*(L"event +ports\*(R". Unfortunately, this mechanism is very buggy in all major +releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get +a large number of spurious wakeups, make sure you have all the relevant +and latest kernel patches applied. No, I don't know which ones, but there +are multiple ones to apply, and afterwards, event ports actually work +great. +.PP +If you can't get it to work, you can try running the program by setting +the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and +\&\f(CW\*(C`select\*(C'\fR backends. +.SS "\s-1AIX POLL BUG\s0" +.IX Subsection "AIX POLL BUG" +\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around +this by trying to avoid the poll backend altogether (i.e. it's not even +compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine +with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway. +.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0" +.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS" +\fIGeneral issues\fR +.IX Subsection "General issues" +.PP +Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev +requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0 +model. Libev still offers limited functionality on this platform in +the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket +descriptors. This only applies when using Win32 natively, not when using +e.g. cygwin. Actually, it only applies to the microsofts own compilers, +as every compiler comes with a slightly differently broken/incompatible +environment. +.PP +Lifting these limitations would basically require the full +re-implementation of the I/O system. If you are into this kind of thing, +then note that glib does exactly that for you in a very portable way (note +also that glib is the slowest event library known to man). +.PP +There is no supported compilation method available on windows except +embedding it into other applications. +.PP +Sensible signal handling is officially unsupported by Microsoft \- libev +tries its best, but under most conditions, signals will simply not work. +.PP +Not a libev limitation but worth mentioning: windows apparently doesn't +accept large writes: instead of resulting in a partial write, windows will +either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large, +so make sure you only write small amounts into your sockets (less than a +megabyte seems safe, but this apparently depends on the amount of memory +available). +.PP +Due to the many, low, and arbitrary limits on the win32 platform and +the abysmal performance of winsockets, using a large number of sockets +is not recommended (and not reasonable). If your program needs to use +more than a hundred or so sockets, then likely it needs to use a totally +different implementation for windows, as libev offers the \s-1POSIX\s0 readiness +notification model, which cannot be implemented efficiently on windows +(due to Microsoft monopoly games). +.PP +A typical way to use libev under windows is to embed it (see the embedding +section for details) and use the following \fIevwrap.h\fR header file instead +of \fIev.h\fR: +.PP +.Vb 2 +\& #define EV_STANDALONE /* keeps ev from requiring config.h */ +\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */ +\& +\& #include "ev.h" +.Ve +.PP +And compile the following \fIevwrap.c\fR file into your project (make sure +you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!): +.PP +.Vb 2 +\& #include "evwrap.h" +\& #include "ev.c" +.Ve +.PP +\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR +.IX Subsection "The winsocket select function" +.PP +The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it +requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is +also extremely buggy). This makes select very inefficient, and also +requires a mapping from file descriptors to socket handles (the Microsoft +C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the +discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and +\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info. +.PP +The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime +libraries and raw winsocket select is: +.PP +.Vb 2 +\& #define EV_USE_SELECT 1 +\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ +.Ve +.PP +Note that winsockets handling of fd sets is O(n), so you can easily get a +complexity in the O(nX) range when using win32. +.PP +\fILimited number of file descriptors\fR +.IX Subsection "Limited number of file descriptors" +.PP +Windows has numerous arbitrary (and low) limits on things. +.PP +Early versions of winsocket's select only supported waiting for a maximum +of \f(CW64\fR handles (probably owning to the fact that all windows kernels +can only wait for \f(CW64\fR things at the same time internally; Microsoft +recommends spawning a chain of threads and wait for 63 handles and the +previous thread in each. Sounds great!). +.PP +Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR +to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select +call (which might be in libev or elsewhere, for example, perl and many +other interpreters do their own select emulation on windows). +.PP +Another limit is the number of file descriptors in the Microsoft runtime +libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR +fetish or something like this inside Microsoft). You can increase this +by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR +(another arbitrary limit), but is broken in many versions of the Microsoft +runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets +(depending on windows version and/or the phase of the moon). To get more, +you need to wrap all I/O functions and provide your own fd management, but +the cost of calling select (O(nX)) will likely make this unworkable. +.SS "\s-1PORTABILITY REQUIREMENTS\s0" +.IX Subsection "PORTABILITY REQUIREMENTS" +In addition to a working ISO-C implementation and of course the +backend-specific APIs, libev relies on a few additional extensions: +.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4 +.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4 +.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *." +Libev assumes not only that all watcher pointers have the same internal +structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also +assumes that the same (machine) code can be used to call any watcher +callback: The watcher callbacks have different type signatures, but libev +calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally. +.IP "null pointers and integer zero are represented by 0 bytes" 4 +.IX Item "null pointers and integer zero are represented by 0 bytes" +Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and +relies on this setting pointers and integers to null. +.IP "pointer accesses must be thread-atomic" 4 +.IX Item "pointer accesses must be thread-atomic" +Accessing a pointer value must be atomic, it must both be readable and +writable in one piece \- this is the case on all current architectures. +.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4 +.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4 +.IX Item "sig_atomic_t volatile must be thread-atomic as well" +The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as +\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different +threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is +believed to be sufficiently portable. +.ie n .IP """sigprocmask"" must work in a threaded environment" 4 +.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4 +.IX Item "sigprocmask must work in a threaded environment" +Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not +allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical +pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main +thread\*(R" or will block signals process-wide, both behaviours would +be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and +\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however. +.Sp +The most portable way to handle signals is to block signals in all threads +except the initial one, and run the signal handling loop in the initial +thread as well. +.ie n .IP """long"" must be large enough for common memory allocation sizes" 4 +.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4 +.IX Item "long must be large enough for common memory allocation sizes" +To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally +instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX +systems (Microsoft...) this might be unexpectedly low, but is still at +least 31 bits everywhere, which is enough for hundreds of millions of +watchers. +.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4 +.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4 +.IX Item "double must hold a time value in seconds with enough accuracy" +The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to +have at least 51 bits of mantissa (and 9 bits of exponent), which is +good enough for at least into the year 4000 with millisecond accuracy +(the design goal for libev). This requirement is overfulfilled by +implementations using \s-1IEEE 754,\s0 which is basically all existing ones. +.Sp +With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the +year 2255 (and millisecond accuracy till the year 287396 \- by then, libev +is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or +something like that, just kidding). +.PP +If you know of other additional requirements drop me a note. +.SH "ALGORITHMIC COMPLEXITIES" +.IX Header "ALGORITHMIC COMPLEXITIES" +In this section the complexities of (many of) the algorithms used inside +libev will be documented. For complexity discussions about backends see +the documentation for \f(CW\*(C`ev_default_init\*(C'\fR. +.PP +All of the following are about amortised time: If an array needs to be +extended, libev needs to realloc and move the whole array, but this +happens asymptotically rarer with higher number of elements, so O(1) might +mean that libev does a lengthy realloc operation in rare cases, but on +average it is much faster and asymptotically approaches constant time. +.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 +.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" +This means that, when you have a watcher that triggers in one hour and +there are 100 watchers that would trigger before that, then inserting will +have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers. +.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4 +.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" +That means that changing a timer costs less than removing/adding them, +as only the relative motion in the event queue has to be paid for. +.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4 +.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" +These just add the watcher into an array or at the head of a list. +.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4 +.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)" +.PD 0 +.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 +.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" +.PD +These watchers are stored in lists, so they need to be walked to find the +correct watcher to remove. The lists are usually short (you don't usually +have many watchers waiting for the same fd or signal: one is typical, two +is rare). +.IP "Finding the next timer in each loop iteration: O(1)" 4 +.IX Item "Finding the next timer in each loop iteration: O(1)" +By virtue of using a binary or 4\-heap, the next timer is always found at a +fixed position in the storage array. +.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 +.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" +A change means an I/O watcher gets started or stopped, which requires +libev to recalculate its status (and possibly tell the kernel, depending +on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used). +.IP "Activating one watcher (putting it into the pending state): O(1)" 4 +.IX Item "Activating one watcher (putting it into the pending state): O(1)" +.PD 0 +.IP "Priority handling: O(number_of_priorities)" 4 +.IX Item "Priority handling: O(number_of_priorities)" +.PD +Priorities are implemented by allocating some space for each +priority. When doing priority-based operations, libev usually has to +linearly search all the priorities, but starting/stopping and activating +watchers becomes O(1) with respect to priority handling. +.IP "Sending an ev_async: O(1)" 4 +.IX Item "Sending an ev_async: O(1)" +.PD 0 +.IP "Processing ev_async_send: O(number_of_async_watchers)" 4 +.IX Item "Processing ev_async_send: O(number_of_async_watchers)" +.IP "Processing signals: O(max_signal_number)" 4 +.IX Item "Processing signals: O(max_signal_number)" +.PD +Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR +calls in the current loop iteration and the loop is currently +blocked. Checking for async and signal events involves iterating over all +running async watchers or all signal numbers. +.SH "PORTING FROM LIBEV 3.X TO 4.X" +.IX Header "PORTING FROM LIBEV 3.X TO 4.X" +The major version 4 introduced some incompatible changes to the \s-1API.\s0 +.PP +At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions +for all changes, so most programs should still compile. The compatibility +layer might be removed in later versions of libev, so better update to the +new \s-1API\s0 early than late. +.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4 +.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4 +.IX Item "EV_COMPAT3 backwards compatibility mechanism" +The backward compatibility mechanism can be controlled by +\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0 +section. +.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4 +.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4 +.IX Item "ev_default_destroy and ev_default_fork have been removed" +These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts: +.Sp +.Vb 2 +\& ev_loop_destroy (EV_DEFAULT_UC); +\& ev_loop_fork (EV_DEFAULT); +.Ve +.IP "function/symbol renames" 4 +.IX Item "function/symbol renames" +A number of functions and symbols have been renamed: +.Sp +.Vb 3 +\& ev_loop => ev_run +\& EVLOOP_NONBLOCK => EVRUN_NOWAIT +\& EVLOOP_ONESHOT => EVRUN_ONCE +\& +\& ev_unloop => ev_break +\& EVUNLOOP_CANCEL => EVBREAK_CANCEL +\& EVUNLOOP_ONE => EVBREAK_ONE +\& EVUNLOOP_ALL => EVBREAK_ALL +\& +\& EV_TIMEOUT => EV_TIMER +\& +\& ev_loop_count => ev_iteration +\& ev_loop_depth => ev_depth +\& ev_loop_verify => ev_verify +.Ve +.Sp +Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an +\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and +associated constants have been renamed to not collide with the \f(CW\*(C`struct +ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme +as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called +\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR +typedef. +.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4 +.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4 +.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES" +The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different +mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile +and work, but the library code will of course be larger. +.SH "GLOSSARY" +.IX Header "GLOSSARY" +.IP "active" 4 +.IX Item "active" +A watcher is active as long as it has been started and not yet stopped. +See \*(L"\s-1WATCHER STATES\*(R"\s0 for details. +.IP "application" 4 +.IX Item "application" +In this document, an application is whatever is using libev. +.IP "backend" 4 +.IX Item "backend" +The part of the code dealing with the operating system interfaces. +.IP "callback" 4 +.IX Item "callback" +The address of a function that is called when some event has been +detected. Callbacks are being passed the event loop, the watcher that +received the event, and the actual event bitset. +.IP "callback/watcher invocation" 4 +.IX Item "callback/watcher invocation" +The act of calling the callback associated with a watcher. +.IP "event" 4 +.IX Item "event" +A change of state of some external event, such as data now being available +for reading on a file descriptor, time having passed or simply not having +any other events happening anymore. +.Sp +In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or +\&\f(CW\*(C`EV_TIMER\*(C'\fR). +.IP "event library" 4 +.IX Item "event library" +A software package implementing an event model and loop. +.IP "event loop" 4 +.IX Item "event loop" +An entity that handles and processes external events and converts them +into callback invocations. +.IP "event model" 4 +.IX Item "event model" +The model used to describe how an event loop handles and processes +watchers and events. +.IP "pending" 4 +.IX Item "pending" +A watcher is pending as soon as the corresponding event has been +detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details. +.IP "real time" 4 +.IX Item "real time" +The physical time that is observed. It is apparently strictly monotonic :) +.IP "wall-clock time" 4 +.IX Item "wall-clock time" +The time and date as shown on clocks. Unlike real time, it can actually +be wrong and jump forwards and backwards, e.g. when you adjust your +clock. +.IP "watcher" 4 +.IX Item "watcher" +A data structure that describes interest in certain events. Watchers need +to be started (attached to an event loop) before they can receive events. +.SH "AUTHOR" +.IX Header "AUTHOR" +Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael +Magnusson and Emanuele Giaquinta, and minor corrections by many others.