Ben Murdoch | 3ef787d | 2012-04-12 10:51:47 +0100 | [diff] [blame^] | 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_ |