1 // Copyright 2012 the V8 project authors. All rights reserved. 2 // Redistribution and use in source and binary forms, with or without 3 // modification, are permitted provided that the following conditions are 4 // met: 5 // 6 // * Redistributions of source code must retain the above copyright 7 // notice, this list of conditions and the following disclaimer. 8 // * Redistributions in binary form must reproduce the above 9 // copyright notice, this list of conditions and the following 10 // disclaimer in the documentation and/or other materials provided 11 // with the distribution. 12 // * Neither the name of Google Inc. nor the names of its 13 // contributors may be used to endorse or promote products derived 14 // from this software without specific prior written permission. 15 // 16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 28 #include "once.h" 29 30 #ifdef _WIN32 31 #include <windows.h> 32 #else 33 #include <sched.h> 34 #endif 35 36 #include "atomicops.h" 37 #include "checks.h" 38 39 namespace v8 { 40 namespace internal { 41 42 void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) { 43 AtomicWord state = Acquire_Load(once); 44 // Fast path. The provided function was already executed. 45 if (state == ONCE_STATE_DONE) { 46 return; 47 } 48 49 // The function execution did not complete yet. The once object can be in one 50 // of the two following states: 51 // - UNINITIALIZED: We are the first thread calling this function. 52 // - EXECUTING_FUNCTION: Another thread is already executing the function. 53 // 54 // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION 55 // atomically. 56 state = Acquire_CompareAndSwap( 57 once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION); 58 if (state == ONCE_STATE_UNINITIALIZED) { 59 // We are the first thread to call this function, so we have to call the 60 // function. 61 init_func(arg); 62 Release_Store(once, ONCE_STATE_DONE); 63 } else { 64 // Another thread has already started executing the function. We need to 65 // wait until it completes the initialization. 66 while (state == ONCE_STATE_EXECUTING_FUNCTION) { 67 #ifdef _WIN32 68 ::Sleep(0); 69 #else 70 sched_yield(); 71 #endif 72 state = Acquire_Load(once); 73 } 74 } 75 } 76 77 } } // namespace v8::internal 78
