/thirdparty/breakpad/third_party/protobuf/protobuf/src/google/protobuf/stubs/once.h

  1// Protocol Buffers - Google's data interchange format
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 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 three things:
 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
 45//   or class member variables of this type).
 46// * A function GogoleOnceInit(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//
 51// This implements a way to perform lazy initialization.  It's more efficient
 52// than using mutexes as no lock is needed if initialization has already
 53// happened.
 54//
 55// Example usage:
 56//   void Init();
 57//   GOOGLE_PROTOBUF_DECLARE_ONCE(once_init);
 58//
 59//   // Calls Init() exactly once.
 60//   void InitOnce() {
 61//     GoogleOnceInit(&once_init, &Init);
 62//   }
 63//
 64// Note that if GoogleOnceInit() is called before main() has begun, it must
 65// only be called by the thread that will eventually call main() -- that is,
 66// the thread that performs dynamic initialization.  In general this is a safe
 67// assumption since people don't usually construct threads before main() starts,
 68// but it is technically not guaranteed.  Unfortunately, Win32 provides no way
 69// whatsoever to statically-initialize its synchronization primitives, so our
 70// only choice is to assume that dynamic initialization is single-threaded.
 71
 72#ifndef GOOGLE_PROTOBUF_STUBS_ONCE_H__
 73#define GOOGLE_PROTOBUF_STUBS_ONCE_H__
 74
 75#include <google/protobuf/stubs/common.h>
 76
 77#ifndef _WIN32
 78#include <pthread.h>
 79#endif
 80
 81namespace google {
 82namespace protobuf {
 83
 84#ifdef _WIN32
 85
 86struct ProtobufOnceInternal;
 87
 88struct LIBPROTOBUF_EXPORT ProtobufOnceType {
 89  ProtobufOnceType();
 90  ~ProtobufOnceType();
 91  void Init(void (*init_func)());
 92
 93  volatile bool initialized_;
 94  ProtobufOnceInternal* internal_;
 95};
 96
 97#define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME)                    \
 98  ::google::protobuf::ProtobufOnceType NAME
 99
100inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
101  // Note:  Double-checked locking is safe on x86.
102  if (!once->initialized_) {
103    once->Init(init_func);
104  }
105}
106
107#else
108
109typedef pthread_once_t ProtobufOnceType;
110
111#define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME)                    \
112  pthread_once_t NAME = PTHREAD_ONCE_INIT
113
114inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
115  pthread_once(once, init_func);
116}
117
118#endif
119
120}  // namespace protobuf
121}  // namespace google
122
123#endif  // GOOGLE_PROTOBUF_STUBS_ONCE_H__