1 // Protocol Buffers - Google's data interchange format 2 // Copyright 2008 Google Inc. All rights reserved. 3 // https://developers.google.com/protocol-buffers/ 4 // 5 // Redistribution and use in source and binary forms, with or without 6 // modification, are permitted provided that the following conditions are 7 // met: 8 // 9 // * Redistributions of source code must retain the above copyright 10 // notice, this list of conditions and the following disclaimer. 11 // * Redistributions in binary form must reproduce the above 12 // copyright notice, this list of conditions and the following disclaimer 13 // in the documentation and/or other materials provided with the 14 // distribution. 15 // * Neither the name of Google Inc. nor the names of its 16 // contributors may be used to endorse or promote products derived from 17 // this software without specific prior written permission. 18 // 19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31 // Author: kenton (at) google.com (Kenton Varda) 32 // 33 // emulates google3/base/once.h 34 // 35 // This header is intended to be included only by internal .cc files and 36 // generated .pb.cc files. Users should not use this directly. 37 // 38 // This is basically a portable version of pthread_once(). 39 // 40 // This header declares: 41 // * A type called ProtobufOnceType. 42 // * A macro GOOGLE_PROTOBUF_DECLARE_ONCE() which declares a variable of type 43 // ProtobufOnceType. This is the only legal way to declare such a variable. 44 // The macro may only be used at the global scope (you cannot create local or 45 // class member variables of this type). 46 // * A function GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()). 47 // This function, when invoked multiple times given the same ProtobufOnceType 48 // object, will invoke init_func on the first call only, and will make sure 49 // none of the calls return before that first call to init_func has finished. 50 // * The user can provide a parameter which GoogleOnceInit() forwards to the 51 // user-provided function when it is called. Usage example: 52 // int a = 10; 53 // GoogleOnceInit(&my_once, &MyFunctionExpectingIntArgument, &a); 54 // * This implementation guarantees that ProtobufOnceType is a POD (i.e. no 55 // static initializer generated). 56 // 57 // This implements a way to perform lazy initialization. It's more efficient 58 // than using mutexes as no lock is needed if initialization has already 59 // happened. 60 // 61 // Example usage: 62 // void Init(); 63 // GOOGLE_PROTOBUF_DECLARE_ONCE(once_init); 64 // 65 // // Calls Init() exactly once. 66 // void InitOnce() { 67 // GoogleOnceInit(&once_init, &Init); 68 // } 69 // 70 // Note that if GoogleOnceInit() is called before main() has begun, it must 71 // only be called by the thread that will eventually call main() -- that is, 72 // the thread that performs dynamic initialization. In general this is a safe 73 // assumption since people don't usually construct threads before main() starts, 74 // but it is technically not guaranteed. Unfortunately, Win32 provides no way 75 // whatsoever to statically-initialize its synchronization primitives, so our 76 // only choice is to assume that dynamic initialization is single-threaded. 77 78 #ifndef GOOGLE_PROTOBUF_STUBS_ONCE_H__ 79 #define GOOGLE_PROTOBUF_STUBS_ONCE_H__ 80 81 #include <google/protobuf/stubs/atomicops.h> 82 #include <google/protobuf/stubs/callback.h> 83 #include <google/protobuf/stubs/common.h> 84 85 namespace google { 86 namespace protobuf { 87 88 #ifdef GOOGLE_PROTOBUF_NO_THREAD_SAFETY 89 90 typedef bool ProtobufOnceType; 91 92 #define GOOGLE_PROTOBUF_ONCE_INIT false 93 94 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) { 95 if (!*once) { 96 *once = true; 97 init_func(); 98 } 99 } 100 101 template <typename Arg> 102 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg), 103 Arg arg) { 104 if (!*once) { 105 *once = true; 106 init_func(arg); 107 } 108 } 109 110 #else 111 112 enum { 113 ONCE_STATE_UNINITIALIZED = 0, 114 ONCE_STATE_EXECUTING_CLOSURE = 1, 115 ONCE_STATE_DONE = 2 116 }; 117 118 typedef internal::AtomicWord ProtobufOnceType; 119 120 #define GOOGLE_PROTOBUF_ONCE_INIT ::google::protobuf::ONCE_STATE_UNINITIALIZED 121 122 LIBPROTOBUF_EXPORT 123 void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure); 124 125 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) { 126 if (internal::Acquire_Load(once) != ONCE_STATE_DONE) { 127 internal::FunctionClosure0 func(init_func, false); 128 GoogleOnceInitImpl(once, &func); 129 } 130 } 131 132 template <typename Arg> 133 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg*), 134 Arg* arg) { 135 if (internal::Acquire_Load(once) != ONCE_STATE_DONE) { 136 internal::FunctionClosure1<Arg*> func(init_func, false, arg); 137 GoogleOnceInitImpl(once, &func); 138 } 139 } 140 141 #endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY 142 143 class GoogleOnceDynamic { 144 public: 145 GoogleOnceDynamic() : state_(GOOGLE_PROTOBUF_ONCE_INIT) { } 146 147 // If this->Init() has not been called before by any thread, 148 // execute (*func_with_arg)(arg) then return. 149 // Otherwise, wait until that prior invocation has finished 150 // executing its function, then return. 151 template<typename T> 152 void Init(void (*func_with_arg)(T*), T* arg) { 153 GoogleOnceInit<T>(&this->state_, 154 func_with_arg, 155 arg); 156 } 157 private: 158 ProtobufOnceType state_; 159 }; 160 161 #define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \ 162 ::google::protobuf::ProtobufOnceType NAME = GOOGLE_PROTOBUF_ONCE_INIT 163 164 } // namespace protobuf 165 } // namespace google 166 167 #endif // GOOGLE_PROTOBUF_STUBS_ONCE_H__ 168
