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Diffstat (limited to 'third_party/protobuf/3.0.0/src/google/protobuf/stubs/once.cc')
-rw-r--r-- | third_party/protobuf/3.0.0/src/google/protobuf/stubs/once.cc | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/third_party/protobuf/3.0.0/src/google/protobuf/stubs/once.cc b/third_party/protobuf/3.0.0/src/google/protobuf/stubs/once.cc new file mode 100644 index 0000000000..889c647660 --- /dev/null +++ b/third_party/protobuf/3.0.0/src/google/protobuf/stubs/once.cc @@ -0,0 +1,99 @@ +// 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 |