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 (at) 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 #include <google/protobuf/stubs/once.h> 39 40 #ifndef GOOGLE_PROTOBUF_NO_THREAD_SAFETY 41 42 #ifdef _WIN32 43 #include <windows.h> 44 #else 45 #include <sched.h> 46 #endif 47 48 #include <google/protobuf/stubs/atomicops.h> 49 50 namespace google { 51 namespace protobuf { 52 53 namespace { 54 55 void SchedYield() { 56 #ifdef _WIN32 57 Sleep(0); 58 #else // POSIX 59 sched_yield(); 60 #endif 61 } 62 63 } // namespace 64 65 void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) { 66 internal::AtomicWord state = internal::Acquire_Load(once); 67 // Fast path. The provided closure was already executed. 68 if (state == ONCE_STATE_DONE) { 69 return; 70 } 71 // The closure execution did not complete yet. The once object can be in one 72 // of the two following states: 73 // - UNINITIALIZED: We are the first thread calling this function. 74 // - EXECUTING_CLOSURE: Another thread is already executing the closure. 75 // 76 // First, try to change the state from UNINITIALIZED to EXECUTING_CLOSURE 77 // atomically. 78 state = internal::Acquire_CompareAndSwap( 79 once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE); 80 if (state == ONCE_STATE_UNINITIALIZED) { 81 // We are the first thread to call this function, so we have to call the 82 // closure. 83 closure->Run(); 84 internal::Release_Store(once, ONCE_STATE_DONE); 85 } else { 86 // Another thread has already started executing the closure. We need to 87 // wait until it completes the initialization. 88 while (state == ONCE_STATE_EXECUTING_CLOSURE) { 89 // Note that futex() could be used here on Linux as an improvement. 90 SchedYield(); 91 state = internal::Acquire_Load(once); 92 } 93 } 94 } 95 96 } // namespace protobuf 97 } // namespace google 98 99 #endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY 100
