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1 // Copyright 2012 the V8 project authors. All rights reserved. | |
2 // Redistribution and use in source and binary forms, with or without | |
3 // modification, are permitted provided that the following conditions are | |
4 // met: | |
5 // | |
6 // * Redistributions of source code must retain the above copyright | |
7 // notice, this list of conditions and the following disclaimer. | |
8 // * Redistributions in binary form must reproduce the above | |
9 // copyright notice, this list of conditions and the following | |
10 // disclaimer in the documentation and/or other materials provided | |
11 // with the distribution. | |
12 // * Neither the name of Google Inc. nor the names of its | |
13 // contributors may be used to endorse or promote products derived | |
14 // from this software without specific prior written permission. | |
15 // | |
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | |
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | |
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
27 | |
28 // emulates google3/base/once.h | |
29 // | |
30 // This header is intended to be included only by v8's internal code. Users | |
31 // should not use this directly. | |
32 // | |
33 // This is basically a portable version of pthread_once(). | |
34 // | |
35 // This header declares: | |
36 // * A type called OnceType. | |
37 // * A macro V8_DECLARE_ONCE() which declares a (global) variable of type | |
38 // OnceType. | |
39 // * A function CallOnce(OnceType* once, void (*init_func)()). | |
40 // This function, when invoked multiple times given the same OnceType object, | |
41 // will invoke init_func on the first call only, and will make sure none of | |
42 // the calls return before that first call to init_func has finished. | |
43 // | |
44 // Additionally, the following features are supported: | |
45 // * A macro V8_ONCE_INIT which is expanded into the expression used to | |
46 // initialize a OnceType. This is only useful when clients embed a OnceType | |
47 // into a structure of their own and want to initialize it statically. | |
48 // * The user can provide a parameter which CallOnce() forwards to the | |
49 // user-provided function when it is called. Usage example: | |
50 // CallOnce(&my_once, &MyFunctionExpectingIntArgument, 10); | |
51 // * This implementation guarantees that OnceType is a POD (i.e. no static | |
52 // initializer generated). | |
53 // | |
54 // This implements a way to perform lazy initialization. It's more efficient | |
55 // than using mutexes as no lock is needed if initialization has already | |
56 // happened. | |
57 // | |
58 // Example usage: | |
59 // void Init(); | |
60 // V8_DECLARE_ONCE(once_init); | |
61 // | |
62 // // Calls Init() exactly once. | |
63 // void InitOnce() { | |
64 // CallOnce(&once_init, &Init); | |
65 // } | |
66 // | |
67 // Note that if CallOnce() is called before main() has begun, it must | |
68 // only be called by the thread that will eventually call main() -- that is, | |
69 // the thread that performs dynamic initialization. In general this is a safe | |
70 // assumption since people don't usually construct threads before main() starts, | |
71 // but it is technically not guaranteed. Unfortunately, Win32 provides no way | |
72 // whatsoever to statically-initialize its synchronization primitives, so our | |
73 // only choice is to assume that dynamic initialization is single-threaded. | |
74 | |
75 #ifndef V8_ONCE_H_ | |
76 #define V8_ONCE_H_ | |
77 | |
78 #include "atomicops.h" | |
79 | |
80 namespace v8 { | |
81 namespace internal { | |
82 | |
83 typedef AtomicWord OnceType; | |
84 | |
85 #define V8_ONCE_INIT 0 | |
86 | |
87 #define V8_DECLARE_ONCE(NAME) ::v8::internal::OnceType NAME | |
88 | |
89 enum { | |
90 ONCE_STATE_UNINITIALIZED = 0, | |
91 ONCE_STATE_EXECUTING_FUNCTION = 1, | |
92 ONCE_STATE_DONE = 2 | |
93 }; | |
94 | |
95 typedef void (*NoArgFunction)(); | |
96 typedef void (*PointerArgFunction)(void* arg); | |
97 | |
98 template <typename T> | |
99 struct OneArgFunction { | |
100 typedef void (*type)(T); | |
101 }; | |
102 | |
103 void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg); | |
104 | |
105 inline void CallOnce(OnceType* once, NoArgFunction init_func) { | |
106 if (Acquire_Load(once) != ONCE_STATE_DONE) { | |
107 CallOnceImpl(once, reinterpret_cast<PointerArgFunction>(init_func), NULL); | |
108 } | |
109 } | |
110 | |
111 | |
112 template <typename Arg> | |
113 inline void CallOnce(OnceType* once, | |
114 typename OneArgFunction<Arg*>::type init_func, Arg* arg) { | |
115 if (Acquire_Load(once) != ONCE_STATE_DONE) { | |
116 CallOnceImpl(once, reinterpret_cast<PointerArgFunction>(init_func), | |
117 static_cast<void*>(arg)); | |
118 } | |
119 } | |
120 | |
121 } } // namespace v8::internal | |
122 | |
123 #endif // V8_ONCE_H_ | |
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