csp2: CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/include/kj/mutex.h comparison

comparison CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/include/kj/mutex.h @ 69:33d812a61356

planemo upload commit 2e9511a184a1ca667c7be0c6321a36dc4e3d116d

author	jpayne
date	Tue, 18 Mar 2025 17:55:14 -0400
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-:0e9998148a16
+:33d812a61356
+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+#pragma once
+#include "debug.h"
+#include "memory.h"
+#include <inttypes.h>
+#include "time.h"
+#include "source-location.h"
+#include "one-of.h"
+KJ_BEGIN_HEADER
+#if __linux__ && !defined(KJ_USE_FUTEX)
+#define KJ_USE_FUTEX 1
+#endif
+#if !KJ_USE_FUTEX && !_WIN32 && !__CYGWIN__
+// We fall back to pthreads when we don't have a better platform-specific primitive. pthreads
+// mutexes are bloated, though, so we like to avoid them. Hence on Linux we use futex(), and on
+// Windows we use SRW locks and friends. On Cygwin we prefer the Win32 primitives both because they
+// are more efficient and because I ran into problems with Cygwin's implementation of RW locks
+// seeming to allow multiple threads to lock the same mutex (but I didn't investigate very
+// closely).
+//
+// TODO(someday):  Write efficient low-level locking primitives for other platforms.
+#include <pthread.h>
+#endif
+// There are 3 macros controlling lock tracking:
+// KJ_TRACK_LOCK_BLOCKING will set up async signal safe TLS variables that can be used to identify
+// the KJ primitive blocking the current thread.
+// KJ_SAVE_ACQUIRED_LOCK_INFO will allow introspection of a Mutex to get information about what is
+// currently holding the lock.
+// KJ_TRACK_LOCK_ACQUISITION is automatically enabled by either one of them.
+#if KJ_TRACK_LOCK_BLOCKING
+// Lock tracking is required to keep track of what blocked.
+#define KJ_TRACK_LOCK_ACQUISITION 1
+#endif
+#if KJ_SAVE_ACQUIRED_LOCK_INFO
+#define KJ_TRACK_LOCK_ACQUISITION 1
+#include <unistd.h>
+#endif
+namespace kj {
+#if KJ_TRACK_LOCK_ACQUISITION
+#if !KJ_USE_FUTEX
+#error Lock tracking is only currently supported for futex-based mutexes.
+#endif
+#if !KJ_COMPILER_SUPPORTS_SOURCE_LOCATION
+#error C++20 or newer is required (or the use of clang/gcc).
+#endif
+using LockSourceLocation = SourceLocation;
+using LockSourceLocationArg = const SourceLocation&;
+// On x86-64 the codegen is optimal if the argument has type const& for the location. However,
+// since this conflicts with the optimal call signature for NoopSourceLocation,
+// LockSourceLocationArg is used to conditionally select the right type without polluting the usage
+// themselves. Interestingly this makes no difference on ARM.
+// https://godbolt.org/z/q6G8ee5a3
+#else
+using LockSourceLocation = NoopSourceLocation;
+using LockSourceLocationArg = NoopSourceLocation;
+#endif
+class Exception;
+// =======================================================================================
+// Private details -- public interfaces follow below.
+namespace _ {  // private
+#if KJ_SAVE_ACQUIRED_LOCK_INFO
+class HoldingExclusively {
+// The lock is being held in exclusive mode.
+public:
+constexpr HoldingExclusively(pid_t tid, const SourceLocation& location)
+: heldBy(tid), acquiredAt(location) {}
+pid_t threadHoldingLock() const { return heldBy; }
+const SourceLocation& lockAcquiredAt() const { return acquiredAt; }
+private:
+pid_t heldBy;
+SourceLocation acquiredAt;
+};
+class HoldingShared {
+// The lock is being held in shared mode currently. Which threads are holding this lock open
+// is unknown.
+public:
+constexpr HoldingShared(const SourceLocation& location) : acquiredAt(location) {}
+const SourceLocation& lockAcquiredAt() const { return acquiredAt; }
+private:
+SourceLocation acquiredAt;
+};
+#endif
+class Mutex {
+// Internal implementation details.  See `MutexGuarded<T>`.
+struct Waiter;
+public:
+Mutex();
+~Mutex();
+KJ_DISALLOW_COPY_AND_MOVE(Mutex);
+enum Exclusivity {
+EXCLUSIVE,
+SHARED
+};
+bool lock(Exclusivity exclusivity, Maybe<Duration> timeout, LockSourceLocationArg location);
+void unlock(Exclusivity exclusivity, Waiter* waiterToSkip = nullptr);
+void assertLockedByCaller(Exclusivity exclusivity) const;
+// In debug mode, assert that the mutex is locked by the calling thread, or if that is
+// non-trivial, assert that the mutex is locked (which should be good enough to catch problems
+// in unit tests).  In non-debug builds, do nothing.
+class Predicate {
+public:
+virtual bool check() = 0;
+};
+void wait(Predicate& predicate, Maybe<Duration> timeout, LockSourceLocationArg location);
+// If predicate.check() returns false, unlock the mutex until predicate.check() returns true, or
+// when the timeout (if any) expires. The mutex is always re-locked when this returns regardless
+// of whether the timeout expired, and including if it throws.
+//
+// Requires that the mutex is already exclusively locked before calling.
+void induceSpuriousWakeupForTest();
+// Utility method for mutex-test.c++ which causes a spurious thread wakeup on all threads that
+// are waiting for a wait() condition. Assuming correct implementation, all those threads
+// should immediately go back to sleep.
+#if KJ_USE_FUTEX
+uint numReadersWaitingForTest() const;
+// The number of reader locks that are currently blocked on this lock (must be called while
+// holding the writer lock). This is really only a utility method for mutex-test.c++ so it can
+// validate certain invariants.
+#endif
+#if KJ_SAVE_ACQUIRED_LOCK_INFO
+using AcquiredMetadata = kj::OneOf<HoldingExclusively, HoldingShared>;
+KJ_DISABLE_TSAN AcquiredMetadata lockedInfo() const;
+// Returns metadata about this lock when its held. This method is async signal safe. It must also
+// be called in a state where it's guaranteed that the lock state won't be released by another
+// thread. In other words this has to be called from the signal handler within the thread that's
+// holding the lock.
+#endif
+private:
+#if KJ_USE_FUTEX
+uint futex;
+// bit 31 (msb) = set if exclusive lock held
+// bit 30 (msb) = set if threads are waiting for exclusive lock
+// bits 0-29 = count of readers; If an exclusive lock is held, this is the count of threads
+//   waiting for a read lock, otherwise it is the count of threads that currently hold a read
+//   lock.
+#ifdef KJ_CONTENTION_WARNING_THRESHOLD
+bool printContendedReader = false;
+#endif
+static constexpr uint EXCLUSIVE_HELD = 1u << 31;
+static constexpr uint EXCLUSIVE_REQUESTED = 1u << 30;
+static constexpr uint SHARED_COUNT_MASK = EXCLUSIVE_REQUESTED - 1;
+#elif _WIN32 || __CYGWIN__
+uintptr_t srwLock;  // Actually an SRWLOCK, but don't want to #include <windows.h> in header.
+#else
+mutable pthread_rwlock_t mutex;
+#endif
+#if KJ_SAVE_ACQUIRED_LOCK_INFO
+pid_t lockedExclusivelyByThread = 0;
+SourceLocation lockAcquiredLocation;
+KJ_DISABLE_TSAN void acquiredExclusive(pid_t tid, const SourceLocation& location) noexcept {
+lockAcquiredLocation = location;
+__atomic_store_n(&lockedExclusivelyByThread, tid, __ATOMIC_RELAXED);
+}
+KJ_DISABLE_TSAN void acquiredShared(const SourceLocation& location) noexcept {
+lockAcquiredLocation = location;
+}
+KJ_DISABLE_TSAN SourceLocation releasingExclusive() noexcept {
+auto tmp = lockAcquiredLocation;
+lockAcquiredLocation = SourceLocation{};
+lockedExclusivelyByThread = 0;
+return tmp;
+}
+#else
+static constexpr void acquiredExclusive(uint, LockSourceLocationArg) {}
+static constexpr void acquiredShared(LockSourceLocationArg) {}
+static constexpr NoopSourceLocation releasingExclusive() { return NoopSourceLocation{}; }
+#endif
+struct Waiter {
+kj::Maybe<Waiter&> next;
+kj::Maybe<Waiter&>* prev;
+Predicate& predicate;
+Maybe<Own<Exception>> exception;
+#if KJ_USE_FUTEX
+uint futex;
+bool hasTimeout;
+#elif _WIN32 || __CYGWIN__
+uintptr_t condvar;
+// Actually CONDITION_VARIABLE, but don't want to #include <windows.h> in header.
+#else
+pthread_cond_t condvar;
+pthread_mutex_t stupidMutex;
+// pthread condvars are only compatible with basic pthread mutexes, not rwlocks, for no
+// particularly good reason. To work around this, we need an extra mutex per condvar.
+#endif
+};
+kj::Maybe<Waiter&> waitersHead = nullptr;
+kj::Maybe<Waiter&>* waitersTail = &waitersHead;
+// linked list of waiters; can only modify under lock
+inline void addWaiter(Waiter& waiter);
+inline void removeWaiter(Waiter& waiter);
+bool checkPredicate(Waiter& waiter);
+#if _WIN32 || __CYGWIN__
+void wakeReadyWaiter(Waiter* waiterToSkip);
+#endif
+};
+class Once {
+// Internal implementation details.  See `Lazy<T>`.
+public:
+#if KJ_USE_FUTEX
+inline Once(bool startInitialized = false)
+: futex(startInitialized ? INITIALIZED : UNINITIALIZED) {}
+#else
+Once(bool startInitialized = false);
+~Once();
+#endif
+KJ_DISALLOW_COPY_AND_MOVE(Once);
+class Initializer {
+public:
+virtual void run() = 0;
+};
+void runOnce(Initializer& init, LockSourceLocationArg location);
+#if _WIN32 || __CYGWIN__  // TODO(perf): Can we make this inline on win32 somehow?
+bool isInitialized() noexcept;
+#else
+inline bool isInitialized() noexcept {
+// Fast path check to see if runOnce() would simply return immediately.
+#if KJ_USE_FUTEX
+return __atomic_load_n(&futex, __ATOMIC_ACQUIRE) == INITIALIZED;
+#else
+return __atomic_load_n(&state, __ATOMIC_ACQUIRE) == INITIALIZED;
+#endif
+}
+#endif
+void reset();
+// Returns the state from initialized to uninitialized.  It is an error to call this when
+// not already initialized, or when runOnce() or isInitialized() might be called concurrently in
+// another thread.
+private:
+#if KJ_USE_FUTEX
+uint futex;
+enum State {
+UNINITIALIZED,
+INITIALIZING,
+INITIALIZING_WITH_WAITERS,
+INITIALIZED
+};
+#elif _WIN32 || __CYGWIN__
+uintptr_t initOnce;  // Actually an INIT_ONCE, but don't want to #include <windows.h> in header.
+#else
+enum State {
+UNINITIALIZED,
+INITIALIZED
+};
+State state;
+pthread_mutex_t mutex;
+#endif
+};
+}  // namespace _ (private)
+// =======================================================================================
+// Public interface
+template <typename T>
+class Locked {
+// Return type for `MutexGuarded<T>::lock()`.  `Locked<T>` provides access to the bounded object
+// and unlocks the mutex when it goes out of scope.
+public:
+KJ_DISALLOW_COPY(Locked);
+inline Locked(): mutex(nullptr), ptr(nullptr) {}
+inline Locked(Locked&& other): mutex(other.mutex), ptr(other.ptr) {
+other.mutex = nullptr;
+other.ptr = nullptr;
+}
+inline ~Locked() {
+if (mutex != nullptr) mutex->unlock(isConst<T>() ? _::Mutex::SHARED : _::Mutex::EXCLUSIVE);
+}
+inline Locked& operator=(Locked&& other) {
+if (mutex != nullptr) mutex->unlock(isConst<T>() ? _::Mutex::SHARED : _::Mutex::EXCLUSIVE);
+mutex = other.mutex;
+ptr = other.ptr;
+other.mutex = nullptr;
+other.ptr = nullptr;
+return *this;
+}
+inline void release() {
+if (mutex != nullptr) mutex->unlock(isConst<T>() ? _::Mutex::SHARED : _::Mutex::EXCLUSIVE);
+mutex = nullptr;
+ptr = nullptr;
+}
+inline T* operator->() { return ptr; }
+inline const T* operator->() const { return ptr; }
+inline T& operator*() { return *ptr; }
+inline const T& operator*() const { return *ptr; }
+inline T* get() { return ptr; }
+inline const T* get() const { return ptr; }
+inline operator T*() { return ptr; }
+inline operator const T*() const { return ptr; }
+template <typename Cond>
+void wait(Cond&& condition, Maybe<Duration> timeout = nullptr,
+LockSourceLocationArg location = {}) {
+// Unlocks the lock until `condition(state)` evaluates true (where `state` is type `const T&`
+// referencing the object protected by the lock).
+// We can't wait on a shared lock because the internal bookkeeping needed for a wait requires
+// the protection of an exclusive lock.
+static_assert(!isConst<T>(), "cannot wait() on shared lock");
+struct PredicateImpl final: public _::Mutex::Predicate {
+bool check() override {
+return condition(value);
+}
+Cond&& condition;
+const T& value;
+PredicateImpl(Cond&& condition, const T& value)
+: condition(kj::fwd<Cond>(condition)), value(value) {}
+};
+PredicateImpl impl(kj::fwd<Cond>(condition), *ptr);
+mutex->wait(impl, timeout, location);
+}
+private:
+_::Mutex* mutex;
+T* ptr;
+inline Locked(_::Mutex& mutex, T& value): mutex(&mutex), ptr(&value) {}
+template <typename U>
+friend class MutexGuarded;
+template <typename U>
+friend class ExternalMutexGuarded;
+#if KJ_MUTEX_TEST
+public:
+#endif
+void induceSpuriousWakeupForTest() { mutex->induceSpuriousWakeupForTest(); }
+// Utility method for mutex-test.c++ which causes a spurious thread wakeup on all threads that
+// are waiting for a when() condition. Assuming correct implementation, all those threads should
+// immediately go back to sleep.
+};
+template <typename T>
+class MutexGuarded {
+// An object of type T, bounded by a mutex.  In order to access the object, you must lock it.
+//
+// Write locks are not "recursive" -- trying to lock again in a thread that already holds a lock
+// will deadlock.  Recursive write locks are usually a sign of bad design.
+//
+// Unfortunately, **READ LOCKS ARE NOT RECURSIVE** either.  Common sense says they should be.
+// But on many operating systems (BSD, OSX), recursively read-locking a pthread_rwlock is
+// actually unsafe.  The problem is that writers are "prioritized" over readers, so a read lock
+// request will block if any write lock requests are outstanding.  So, if thread A takes a read
+// lock, thread B requests a write lock (and starts waiting), and then thread A tries to take
+// another read lock recursively, the result is deadlock.
+public:
+template <typename... Params>
+explicit MutexGuarded(Params&&... params);
+// Initialize the mutex-bounded object by passing the given parameters to its constructor.
+Locked<T> lockExclusive(LockSourceLocationArg location = {}) const;
+// Exclusively locks the object and returns it.  The returned `Locked<T>` can be passed by
+// move, similar to `Own<T>`.
+//
+// This method is declared `const` in accordance with KJ style rules which say that constness
+// should be used to indicate thread-safety.  It is safe to share a const pointer between threads,
+// but it is not safe to share a mutable pointer.  Since the whole point of MutexGuarded is to
+// be shared between threads, its methods should be const, even though locking it produces a
+// non-const pointer to the contained object.
+Locked<const T> lockShared(LockSourceLocationArg location = {}) const;
+// Lock the value for shared access.  Multiple shared locks can be taken concurrently, but cannot
+// be held at the same time as a non-shared lock.
+Maybe<Locked<T>> lockExclusiveWithTimeout(Duration timeout,
+LockSourceLocationArg location = {}) const;
+// Attempts to exclusively lock the object. If the timeout elapses before the lock is acquired,
+// this returns null.
+Maybe<Locked<const T>> lockSharedWithTimeout(Duration timeout,
+LockSourceLocationArg location = {}) const;
+// Attempts to lock the value for shared access. If the timeout elapses before the lock is acquired,
+// this returns null.
+inline const T& getWithoutLock() const { return value; }
+inline T& getWithoutLock() { return value; }
+// Escape hatch for cases where some external factor guarantees that it's safe to get the
+// value.  You should treat these like const_cast -- be highly suspicious of any use.
+inline const T& getAlreadyLockedShared() const;
+inline T& getAlreadyLockedShared();
+inline T& getAlreadyLockedExclusive() const;
+// Like `getWithoutLock()`, but asserts that the lock is already held by the calling thread.
+template <typename Cond, typename Func>
+auto when(Cond&& condition, Func&& callback, Maybe<Duration> timeout = nullptr,
+LockSourceLocationArg location = {}) const
+-> decltype(callback(instance<T&>())) {
+// Waits until condition(state) returns true, then calls callback(state) under lock.
+//
+// `condition`, when called, receives as its parameter a const reference to the state, which is
+// locked (either shared or exclusive). `callback` receives a mutable reference, which is
+// exclusively locked.
+//
+// `condition()` may be called multiple times, from multiple threads, while waiting for the
+// condition to become true. It may even return true once, but then be called more times.
+// It is guaranteed, though, that at the time `callback()` is finally called, `condition()`
+// would currently return true (assuming it is a pure function of the guarded data).
+//
+// If `timeout` is specified, then after the given amount of time, the callback will be called
+// regardless of whether the condition is true. In this case, when `callback()` is called,
+// `condition()` may in fact evaluate false, but *only* if the timeout was reached.
+//
+// TODO(cleanup): lock->wait() is a better interface. Can we deprecate this one?
+auto lock = lockExclusive();
+lock.wait(kj::fwd<Cond>(condition), timeout, location);
+return callback(value);
+}
+private:
+mutable _::Mutex mutex;
+mutable T value;
+};
+template <typename T>
+class MutexGuarded<const T> {
+// MutexGuarded cannot guard a const type.  This would be pointless anyway, and would complicate
+// the implementation of Locked<T>, which uses constness to decide what kind of lock it holds.
+static_assert(sizeof(T) < 0, "MutexGuarded's type cannot be const.");
+};
+template <typename T>
+class ExternalMutexGuarded {
+// Holds a value that can only be manipulated while some other mutex is locked.
+//
+// The ExternalMutexGuarded<T> lives *outside* the scope of any lock on the mutex, but ensures
+// that the value it holds can only be accessed under lock by forcing the caller to present a
+// lock before accessing the value.
+//
+// Additionally, ExternalMutexGuarded<T>'s destructor will take an exclusive lock on the mutex
+// while destroying the held value, unless the value has been release()ed before hand.
+//
+// The type T must have the following properties (which probably all movable types satisfy):
+// - T is movable.
+// - Immediately after any of the following has happened, T's destructor is effectively a no-op
+//   (hence certainly not requiring locks):
+//   - The value has been default-constructed.
+//   - The value has been initialized by-move from a default-constructed T.
+//   - The value has been moved away.
+// - If ExternalMutexGuarded<T> is ever moved, then T must have a move constructor and move
+//   assignment operator that do not follow any pointers, therefore do not need to take a lock.
+//
+// Inherits from LockSourceLocation to perform an empty base class optimization when lock tracking
+// is compiled out. Once the minimum C++ standard for the KJ library is C++20, this optimization
+// could be replaced by a member variable with a [[no_unique_address]] annotation.
+public:
+ExternalMutexGuarded(LockSourceLocationArg location = {})
+: location(location) {}
+template <typename U, typename... Params>
+ExternalMutexGuarded(Locked<U> lock, Params&&... params, LockSourceLocationArg location = {})
+: mutex(lock.mutex),
+value(kj::fwd<Params>(params)...),
+location(location) {}
+// Construct the value in-place. This constructor requires passing ownership of the lock into
+// the constructor. Normally this should be a lock that you take on the line calling the
+// constructor, like:
+//
+//     ExternalMutexGuarded<T> foo(someMutexGuarded.lockExclusive());
+//
+// The reason this constructor does not accept an lvalue reference to an existing lock is because
+// this would be deadlock-prone: If an exception were thrown immediately after the constructor
+// completed, then the destructor would deadlock, because the lock would still be held. An
+// ExternalMutexGuarded must live outside the scope of any locks to avoid such a deadlock.
+~ExternalMutexGuarded() noexcept(false) {
+if (mutex != nullptr) {
+mutex->lock(_::Mutex::EXCLUSIVE, nullptr, location);
+KJ_DEFER(mutex->unlock(_::Mutex::EXCLUSIVE));
+value = T();
+}
+}
+ExternalMutexGuarded(ExternalMutexGuarded&& other)
+: mutex(other.mutex), value(kj::mv(other.value)), location(other.location) {
+other.mutex = nullptr;
+}
+ExternalMutexGuarded& operator=(ExternalMutexGuarded&& other) {
+mutex = other.mutex;
+value = kj::mv(other.value);
+location = other.location;
+other.mutex = nullptr;
+return *this;
+}
+template <typename U>
+void set(Locked<U>& lock, T&& newValue) {
+KJ_IREQUIRE(mutex == nullptr);
+mutex = lock.mutex;
+value = kj::mv(newValue);
+}
+template <typename U>
+T& get(Locked<U>& lock) {
+KJ_IREQUIRE(lock.mutex == mutex);
+return value;
+}
+template <typename U>
+const T& get(Locked<const U>& lock) const {
+KJ_IREQUIRE(lock.mutex == mutex);
+return value;
+}
+template <typename U>
+T release(Locked<U>& lock) {
+// Release (move away) the value. This allows the destructor to skip locking the mutex.
+KJ_IREQUIRE(lock.mutex == mutex);
+T result = kj::mv(value);
+mutex = nullptr;
+return result;
+}
+private:
+_::Mutex* mutex = nullptr;
+T value;
+KJ_NO_UNIQUE_ADDRESS LockSourceLocation location;
+// When built against C++20 (or clang >= 9.0), the overhead of this is elided. Otherwise this
+// struct will be 1 byte larger than it would otherwise be.
+};
+template <typename T>
+class Lazy {
+// A lazily-initialized value.
+public:
+template <typename Func>
+T& get(Func&& init, LockSourceLocationArg location = {});
+template <typename Func>
+const T& get(Func&& init, LockSourceLocationArg location = {}) const;
+// The first thread to call get() will invoke the given init function to construct the value.
+// Other threads will block until construction completes, then return the same value.
+//
+// `init` is a functor(typically a lambda) which takes `SpaceFor<T>&` as its parameter and returns
+// `Own<T>`.  If `init` throws an exception, the exception is propagated out of that thread's
+// call to `get()`, and subsequent calls behave as if `get()` hadn't been called at all yet --
+// in other words, subsequent calls retry initialization until it succeeds.
+private:
+mutable _::Once once;
+mutable SpaceFor<T> space;
+mutable Own<T> value;
+template <typename Func>
+class InitImpl;
+};
+// =======================================================================================
+// Inline implementation details
+template <typename T>
+template <typename... Params>
+inline MutexGuarded<T>::MutexGuarded(Params&&... params)
+: value(kj::fwd<Params>(params)...) {}
+template <typename T>
+inline Locked<T> MutexGuarded<T>::lockExclusive(LockSourceLocationArg location)
+const {
+mutex.lock(_::Mutex::EXCLUSIVE, nullptr, location);
+return Locked<T>(mutex, value);
+}
+template <typename T>
+inline Locked<const T> MutexGuarded<T>::lockShared(LockSourceLocationArg location) const {
+mutex.lock(_::Mutex::SHARED, nullptr, location);
+return Locked<const T>(mutex, value);
+}
+template <typename T>
+inline Maybe<Locked<T>> MutexGuarded<T>::lockExclusiveWithTimeout(Duration timeout,
+LockSourceLocationArg location) const {
+if (mutex.lock(_::Mutex::EXCLUSIVE, timeout, location)) {
+return Locked<T>(mutex, value);
+} else {
+return nullptr;
+}
+}
+template <typename T>
+inline Maybe<Locked<const T>> MutexGuarded<T>::lockSharedWithTimeout(Duration timeout,
+LockSourceLocationArg location) const {
+if (mutex.lock(_::Mutex::SHARED, timeout, location)) {
+return Locked<const T>(mutex, value);
+} else {
+return nullptr;
+}
+}
+template <typename T>
+inline const T& MutexGuarded<T>::getAlreadyLockedShared() const {
+#ifdef KJ_DEBUG
+mutex.assertLockedByCaller(_::Mutex::SHARED);
+#endif
+return value;
+}
+template <typename T>
+inline T& MutexGuarded<T>::getAlreadyLockedShared() {
+#ifdef KJ_DEBUG
+mutex.assertLockedByCaller(_::Mutex::SHARED);
+#endif
+return value;
+}
+template <typename T>
+inline T& MutexGuarded<T>::getAlreadyLockedExclusive() const {
+#ifdef KJ_DEBUG
+mutex.assertLockedByCaller(_::Mutex::EXCLUSIVE);
+#endif
+return const_cast<T&>(value);
+}
+template <typename T>
+template <typename Func>
+class Lazy<T>::InitImpl: public _::Once::Initializer {
+public:
+inline InitImpl(const Lazy<T>& lazy, Func&& func): lazy(lazy), func(kj::fwd<Func>(func)) {}
+void run() override {
+lazy.value = func(lazy.space);
+}
+private:
+const Lazy<T>& lazy;
+Func func;
+};
+template <typename T>
+template <typename Func>
+inline T& Lazy<T>::get(Func&& init, LockSourceLocationArg location) {
+if (!once.isInitialized()) {
+InitImpl<Func> initImpl(*this, kj::fwd<Func>(init));
+once.runOnce(initImpl, location);
+}
+return *value;
+}
+template <typename T>
+template <typename Func>
+inline const T& Lazy<T>::get(Func&& init, LockSourceLocationArg location) const {
+if (!once.isInitialized()) {
+InitImpl<Func> initImpl(*this, kj::fwd<Func>(init));
+once.runOnce(initImpl, location);
+}
+return *value;
+}
+#if KJ_TRACK_LOCK_BLOCKING
+struct BlockedOnMutexAcquisition {
+const _::Mutex& mutex;
+// The mutex we are blocked on.
+const SourceLocation& origin;
+// Where did the blocking operation originate from.
+};
+struct BlockedOnCondVarWait {
+const _::Mutex& mutex;
+// The mutex the condition variable is using (may or may not be locked).
+const void* waiter;
+// Pointer to the waiter that's being waited on.
+const SourceLocation& origin;
+// Where did the blocking operation originate from.
+};
+struct BlockedOnOnceInit {
+const _::Once& once;
+const SourceLocation& origin;
+// Where did the blocking operation originate from.
+};
+using BlockedOnReason = OneOf<BlockedOnMutexAcquisition, BlockedOnCondVarWait, BlockedOnOnceInit>;
+Maybe<const BlockedOnReason&> blockedReason() noexcept;
+// Returns the information about the reason the current thread is blocked synchronously on KJ
+// lock primitives. Returns nullptr if the current thread is not currently blocked on such
+// primitives. This is intended to be called from a signal handler to check whether the current
+// thread is blocked. Outside of a signal handler there is little value to this function. In those
+// cases by definition the thread is not blocked. This includes the callable used as part of a
+// condition variable since that happens after the lock is acquired & the current thread is no
+// longer blocked). The utility could be made useful for non-signal handler use-cases by being able
+// to fetch the pointer to the TLS variable directly (i.e. const BlockedOnReason&*). However, there
+// would have to be additional changes/complexity to try make that work since you'd need
+// synchronization to ensure that the memory you'd try to reference is still valid. The likely
+// solution would be to make these mutually exclusive options where you can use either the fast
+// async-safe option, or a mutex-guarded TLS variable you can get a reference to that isn't
+// async-safe. That being said, maybe someone can come up with a way to make something that works
+// in both use-cases which would of course be more preferable.
+#endif
+}  // namespace kj
+KJ_END_HEADER

Mercurial > repos > rliterman > csp2

comparison CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/include/kj/mutex.h @ 69:33d812a61356