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@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
84 namespace google {
85 namespace protobuf {
86
87 #ifdef GOOGLE_PROTOBUF_NO_THREAD_SAFETY
88
89 typedef bool ProtobufOnceType;
90
91 #define GOOGLE_PROTOBUF_ONCE_INIT false
92
GoogleOnceInit(ProtobufOnceType * once,void (* init_func)())93 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
94 if (!*once) {
95 *once = true;
96 init_func();
97 }
98 }
99
100 template <typename Arg>
GoogleOnceInit(ProtobufOnceType * once,void (* init_func)(Arg),Arg arg)101 inline 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
111 enum {
112 ONCE_STATE_UNINITIALIZED = 0,
113 ONCE_STATE_EXECUTING_CLOSURE = 1,
114 ONCE_STATE_DONE = 2
115 };
116
117 typedef internal::AtomicWord ProtobufOnceType;
118
119 #define GOOGLE_PROTOBUF_ONCE_INIT ::google::protobuf::ONCE_STATE_UNINITIALIZED
120
121 LIBPROTOBUF_EXPORT
122 void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure);
123
124 inline 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
131 template <typename Arg>
132 inline 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 class GoogleOnceDynamic {
143 public:
GoogleOnceDynamic()144 GoogleOnceDynamic() : state_(GOOGLE_PROTOBUF_ONCE_INIT) { }
145
146 // If this->Init() has not been called before by any thread,
147 // execute (*func_with_arg)(arg) then return.
148 // Otherwise, wait until that prior invocation has finished
149 // executing its function, then return.
150 template<typename T>
Init(void (* func_with_arg)(T *),T * arg)151 void Init(void (*func_with_arg)(T*), T* arg) {
152 GoogleOnceInit<T>(&this->state_,
153 func_with_arg,
154 arg);
155 }
156 private:
157 ProtobufOnceType state_;
158 };
159
160 #define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \
161 ::google::protobuf::ProtobufOnceType NAME = GOOGLE_PROTOBUF_ONCE_INIT
162
163 } // namespace protobuf
164 } // namespace google
165
166 #endif // GOOGLE_PROTOBUF_STUBS_ONCE_H__
167