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 #elif defined(V8_OS_STARBOARD) 10 #include "starboard/thread.h" 11 #else 12 #include <sched.h> 13 #endif 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 // Fast path. The provided function was already executed. 20 if (once->load(std::memory_order_acquire) == ONCE_STATE_DONE) { 21 return; 22 } 23 24 // The function execution did not complete yet. The once object can be in one 25 // of the two following states: 26 // - UNINITIALIZED: We are the first thread calling this function. 27 // - EXECUTING_FUNCTION: Another thread is already executing the function. 28 // 29 // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION 30 // atomically. 31 uint8_t expected = ONCE_STATE_UNINITIALIZED; 32 if (once->compare_exchange_strong(expected, ONCE_STATE_EXECUTING_FUNCTION, 33 std::memory_order_acq_rel)) { 34 // We are the first thread to call this function, so we have to call the 35 // function. 36 init_func(); 37 once->store(ONCE_STATE_DONE, std::memory_order_release); 38 } else { 39 // Another thread has already started executing the function. We need to 40 // wait until it completes the initialization. 41 while (once->load(std::memory_order_acquire) == 42 ONCE_STATE_EXECUTING_FUNCTION) { 43 #ifdef _WIN32 44 ::Sleep(0); 45 #elif defined(V8_OS_STARBOARD) 46 SbThreadYield(); 47 #else 48 sched_yield(); 49 #endif 50 } 51 } 52 } 53 54 } // namespace base 55 } // namespace v8 56