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 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
81 namespace google {
82 namespace protobuf {
83
84 #ifdef _WIN32
85
86 struct ProtobufOnceInternal;
87
88 struct 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
GoogleOnceInit(ProtobufOnceType * once,void (* init_func)())100 inline 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
109 typedef pthread_once_t ProtobufOnceType;
110
111 #define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \
112 pthread_once_t NAME = PTHREAD_ONCE_INIT
113
114 inline 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__
124