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