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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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