1// Protocol Buffers - Google's data interchange format 2// Copyright 2008 Google Inc. All rights reserved. 3// http://code.google.com/p/protobuf/ 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@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/common.h> 83 84namespace google { 85namespace protobuf { 86 87#ifdef GOOGLE_PROTOBUF_NO_THREAD_SAFETY 88 89typedef bool ProtobufOnceType; 90 91#define GOOGLE_PROTOBUF_ONCE_INIT false 92 93inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) { 94 if (!*once) { 95 *once = true; 96 init_func(); 97 } 98} 99 100template <typename Arg> 101inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg), 102 Arg arg) { 103 if (!*once) { 104 *once = true; 105 init_func(arg); 106 } 107} 108 109#else 110 111enum { 112 ONCE_STATE_UNINITIALIZED = 0, 113 ONCE_STATE_EXECUTING_CLOSURE = 1, 114 ONCE_STATE_DONE = 2 115}; 116 117typedef internal::AtomicWord ProtobufOnceType; 118 119#define GOOGLE_PROTOBUF_ONCE_INIT ::google::protobuf::ONCE_STATE_UNINITIALIZED 120 121LIBPROTOBUF_EXPORT 122void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure); 123 124inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) { 125 if (internal::Acquire_Load(once) != ONCE_STATE_DONE) { 126 internal::FunctionClosure0 func(init_func, false); 127 GoogleOnceInitImpl(once, &func); 128 } 129} 130 131template <typename Arg> 132inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg*), 133 Arg* arg) { 134 if (internal::Acquire_Load(once) != ONCE_STATE_DONE) { 135 internal::FunctionClosure1<Arg*> func(init_func, false, arg); 136 GoogleOnceInitImpl(once, &func); 137 } 138} 139 140#endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY 141 142#define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \ 143 ::google::protobuf::ProtobufOnceType NAME = GOOGLE_PROTOBUF_ONCE_INIT 144 145} // namespace protobuf 146} // namespace google 147 148#endif // GOOGLE_PROTOBUF_STUBS_ONCE_H__ 149