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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// Author: kenton@google.com (Kenton Varda)
//
// emulates google3/base/once.h
//
// This header is intended to be included only by internal .cc files and
// generated .pb.cc files. Users should not use this directly.
#include <google/protobuf/stubs/once.h>
#ifndef GOOGLE_PROTOBUF_NO_THREAD_SAFETY
#ifdef _WIN32
#include <windows.h>
#else
#include <sched.h>
#endif
#include <google/protobuf/stubs/atomicops.h>
namespace google {
namespace protobuf {
namespace {
void SchedYield() {
#ifdef _WIN32
Sleep(0);
#else // POSIX
sched_yield();
#endif
}
} // namespace
void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
internal::AtomicWord state = internal::Acquire_Load(once);
// Fast path. The provided closure was already executed.
if (state == ONCE_STATE_DONE) {
return;
}
// The closure execution did not complete yet. The once object can be in one
// of the two following states:
// - UNINITIALIZED: We are the first thread calling this function.
// - EXECUTING_CLOSURE: Another thread is already executing the closure.
//
// First, try to change the state from UNINITIALIZED to EXECUTING_CLOSURE
// atomically.
state = internal::Acquire_CompareAndSwap(
once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE);
if (state == ONCE_STATE_UNINITIALIZED) {
// We are the first thread to call this function, so we have to call the
// closure.
closure->Run();
internal::Release_Store(once, ONCE_STATE_DONE);
} else {
// Another thread has already started executing the closure. We need to
// wait until it completes the initialization.
while (state == ONCE_STATE_EXECUTING_CLOSURE) {
// Note that futex() could be used here on Linux as an improvement.
SchedYield();
state = internal::Acquire_Load(once);
}
}
}
} // namespace protobuf
} // namespace google
#endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY
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