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

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planemo upload commit 2e9511a184a1ca667c7be0c6321a36dc4e3d116d
author jpayne
date Tue, 18 Mar 2025 17:55:14 -0400
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1 // Copyright (c) 2014, Jason Choy <jjwchoy@gmail.com>
2 // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
3 // Licensed under the MIT License:
4 //
5 // Permission is hereby granted, free of charge, to any person obtaining a copy
6 // of this software and associated documentation files (the "Software"), to deal
7 // in the Software without restriction, including without limitation the rights
8 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9 // copies of the Software, and to permit persons to whom the Software is
10 // furnished to do so, subject to the following conditions:
11 //
12 // The above copyright notice and this permission notice shall be included in
13 // all copies or substantial portions of the Software.
14 //
15 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
21 // THE SOFTWARE.
22
23 #pragma once
24
25 // This file declares a macro `KJ_THREADLOCAL_PTR` for declaring thread-local pointer-typed
26 // variables. Use like:
27 // KJ_THREADLOCAL_PTR(MyType) foo = nullptr;
28 // This is equivalent to:
29 // thread_local MyType* foo = nullptr;
30 // This can only be used at the global scope.
31 //
32 // AVOID USING THIS. Use of thread-locals is discouraged because they often have many of the same
33 // properties as singletons: http://www.object-oriented-security.org/lets-argue/singletons
34 //
35 // Also, thread-locals tend to be hostile to event-driven code, which can be particularly
36 // surprising when using fibers (all fibers in the same thread will share the same threadlocals,
37 // even though they do not share a stack).
38 //
39 // That said, thread-locals are sometimes needed for runtime logistics in the KJ framework. For
40 // example, the current exception callback and current EventLoop are stored as thread-local
41 // pointers. Since KJ only ever needs to store pointers, not values, we avoid the question of
42 // whether these values' destructors need to be run, and we avoid the need for heap allocation.
43
44 #include "common.h"
45
46 KJ_BEGIN_HEADER
47
48 namespace kj {
49
50 #if __GNUC__
51
52 #define KJ_THREADLOCAL_PTR(type) static __thread type*
53 // GCC's __thread is lighter-weight than thread_local and is good enough for our purposes.
54 //
55 // TODO(cleanup): The above comment was written many years ago. Is it still true? Shouldn't the
56 // compiler be smart enough to optimize a thread_local of POD type?
57
58 #else
59
60 #define KJ_THREADLOCAL_PTR(type) static thread_local type*
61
62 #endif // KJ_USE_PTHREAD_TLS
63
64 } // namespace kj
65
66 KJ_END_HEADER