124 lines
4.5 KiB
C++
124 lines
4.5 KiB
C++
// Protocol Buffers - Google's data interchange format
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// Copyright 2008 Google Inc. All rights reserved.
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// http://code.google.com/p/protobuf/
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// Author: kenton@google.com (Kenton Varda)
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//
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// emulates google3/base/once.h
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//
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// This header is intended to be included only by internal .cc files and
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// generated .pb.cc files. Users should not use this directly.
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//
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// This is basically a portable version of pthread_once().
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//
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// This header declares three things:
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// * A type called ProtobufOnceType.
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// * A macro GOOGLE_PROTOBUF_DECLARE_ONCE() which declares a variable of type
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// ProtobufOnceType. This is the only legal way to declare such a variable.
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// The macro may only be used at the global scope (you cannot create local
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// or class member variables of this type).
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// * A function GogoleOnceInit(ProtobufOnceType* once, void (*init_func)()).
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// This function, when invoked multiple times given the same ProtobufOnceType
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// object, will invoke init_func on the first call only, and will make sure
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// none of the calls return before that first call to init_func has finished.
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//
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// This implements a way to perform lazy initialization. It's more efficient
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// than using mutexes as no lock is needed if initialization has already
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// happened.
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//
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// Example usage:
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// void Init();
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// GOOGLE_PROTOBUF_DECLARE_ONCE(once_init);
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//
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// // Calls Init() exactly once.
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// void InitOnce() {
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// GoogleOnceInit(&once_init, &Init);
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// }
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//
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// Note that if GoogleOnceInit() is called before main() has begun, it must
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// only be called by the thread that will eventually call main() -- that is,
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// the thread that performs dynamic initialization. In general this is a safe
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// assumption since people don't usually construct threads before main() starts,
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// but it is technically not guaranteed. Unfortunately, Win32 provides no way
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// whatsoever to statically-initialize its synchronization primitives, so our
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// only choice is to assume that dynamic initialization is single-threaded.
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#ifndef GOOGLE_PROTOBUF_STUBS_ONCE_H__
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#define GOOGLE_PROTOBUF_STUBS_ONCE_H__
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#include <google/protobuf/stubs/common.h>
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#ifndef _WIN32
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#include <pthread.h>
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#endif
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namespace google {
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namespace protobuf {
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#ifdef _WIN32
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struct ProtobufOnceInternal;
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struct LIBPROTOBUF_EXPORT ProtobufOnceType {
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ProtobufOnceType();
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~ProtobufOnceType();
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void Init(void (*init_func)());
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volatile bool initialized_;
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ProtobufOnceInternal* internal_;
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};
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#define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \
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::google::protobuf::ProtobufOnceType NAME
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inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
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// Note: Double-checked locking is safe on x86.
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if (!once->initialized_) {
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once->Init(init_func);
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}
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}
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#else
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typedef pthread_once_t ProtobufOnceType;
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#define GOOGLE_PROTOBUF_DECLARE_ONCE(NAME) \
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pthread_once_t NAME = PTHREAD_ONCE_INIT
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inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
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pthread_once(once, init_func);
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}
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#endif
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} // namespace protobuf
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} // namespace google
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#endif // GOOGLE_PROTOBUF_STUBS_ONCE_H__
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