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 15 namespace v8 { 16 namespace base { 17 CallOnceImpl(OnceType * once,std::function<void ()> init_func)18void CallOnceImpl(OnceType* once, std::function<void()> init_func) { 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(); 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