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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/callback.h>
83 #include <google/protobuf/stubs/common.h>
84 
85 namespace google {
86 namespace protobuf {
87 
88 #ifdef GOOGLE_PROTOBUF_NO_THREAD_SAFETY
89 
90 typedef bool ProtobufOnceType;
91 
92 #define GOOGLE_PROTOBUF_ONCE_INIT false
93 
GoogleOnceInit(ProtobufOnceType * once,void (* init_func)())94 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
95   if (!*once) {
96     *once = true;
97     init_func();
98   }
99 }
100 
101 template <typename Arg>
GoogleOnceInit(ProtobufOnceType * once,void (* init_func)(Arg),Arg arg)102 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg),
103     Arg arg) {
104   if (!*once) {
105     *once = true;
106     init_func(arg);
107   }
108 }
109 
110 #else
111 
112 enum {
113   ONCE_STATE_UNINITIALIZED = 0,
114   ONCE_STATE_EXECUTING_CLOSURE = 1,
115   ONCE_STATE_DONE = 2
116 };
117 
118 typedef internal::AtomicWord ProtobufOnceType;
119 
120 #define GOOGLE_PROTOBUF_ONCE_INIT ::google::protobuf::ONCE_STATE_UNINITIALIZED
121 
122 LIBPROTOBUF_EXPORT
123 void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure);
124 
125 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
126   if (internal::Acquire_Load(once) != ONCE_STATE_DONE) {
127     internal::FunctionClosure0 func(init_func, false);
128     GoogleOnceInitImpl(once, &func);
129   }
130 }
131 
132 template <typename Arg>
133 inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg*),
134     Arg* arg) {
135   if (internal::Acquire_Load(once) != ONCE_STATE_DONE) {
136     internal::FunctionClosure1<Arg*> func(init_func, false, arg);
137     GoogleOnceInitImpl(once, &func);
138   }
139 }
140 
141 #endif  // GOOGLE_PROTOBUF_NO_THREAD_SAFETY
142 
143 class GoogleOnceDynamic {
144  public:
GoogleOnceDynamic()145   GoogleOnceDynamic() : state_(GOOGLE_PROTOBUF_ONCE_INIT) { }
146 
147   // If this->Init() has not been called before by any thread,
148   // execute (*func_with_arg)(arg) then return.
149   // Otherwise, wait until that prior invocation has finished
150   // executing its function, then return.
151   template<typename T>
Init(void (* func_with_arg)(T *),T * arg)152   void Init(void (*func_with_arg)(T*), T* arg) {
153     GoogleOnceInit<T>(&this->state_,
154                       func_with_arg,
155                       arg);
156   }
157  private:
158   ProtobufOnceType state_;
159 };
160 
161 #define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \
162   ::google::protobuf::ProtobufOnceType NAME = GOOGLE_PROTOBUF_ONCE_INIT
163 
164 }  // namespace protobuf
165 }  // namespace google
166 
167 #endif  // GOOGLE_PROTOBUF_STUBS_ONCE_H__
168