| // Protocol Buffers - Google's data interchange format |
| // Copyright 2008 Google Inc. All rights reserved. |
| // http://code.google.com/p/protobuf/ |
| // |
| // 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 |
