1// Copyright 2012 the V8 project authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#include "src/base/once.h" 6 7#ifdef _WIN32 8#include <windows.h> 9#else 10#include <sched.h> 11#endif 12 13#include "src/base/atomicops.h" 14 15namespace v8 { 16namespace base { 17 18void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) { 19 AtomicWord state = Acquire_Load(once); 20 // Fast path. The provided function was already executed. 21 if (state == ONCE_STATE_DONE) { 22 return; 23 } 24 25 // The function execution did not complete yet. The once object can be in one 26 // of the two following states: 27 // - UNINITIALIZED: We are the first thread calling this function. 28 // - EXECUTING_FUNCTION: Another thread is already executing the function. 29 // 30 // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION 31 // atomically. 32 state = Acquire_CompareAndSwap( 33 once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION); 34 if (state == ONCE_STATE_UNINITIALIZED) { 35 // We are the first thread to call this function, so we have to call the 36 // function. 37 init_func(arg); 38 Release_Store(once, ONCE_STATE_DONE); 39 } else { 40 // Another thread has already started executing the function. We need to 41 // wait until it completes the initialization. 42 while (state == ONCE_STATE_EXECUTING_FUNCTION) { 43#ifdef _WIN32 44 ::Sleep(0); 45#else 46 sched_yield(); 47#endif 48 state = Acquire_Load(once); 49 } 50 } 51} 52 53} // namespace base 54} // namespace v8 55