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// Copyright 2012 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #include "src/base/once.h" #ifdef _WIN32 #include <windows.h> #else #include <sched.h> #endif namespace v8 { namespace base { void CallOnceImpl(OnceType* once, std::function<void()> init_func) { // Fast path. The provided function was already executed. if (once->load(std::memory_order_acquire) == ONCE_STATE_DONE) { return; } // The function execution did not complete yet. The once object can be in one // of the two following states: // - UNINITIALIZED: We are the first thread calling this function. // - EXECUTING_FUNCTION: Another thread is already executing the function. // // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION // atomically. uint8_t expected = ONCE_STATE_UNINITIALIZED; if (once->compare_exchange_strong(expected, ONCE_STATE_EXECUTING_FUNCTION, std::memory_order_acq_rel)) { // We are the first thread to call this function, so we have to call the // function. init_func(); once->store(ONCE_STATE_DONE, std::memory_order_release); } else { // Another thread has already started executing the function. We need to // wait until it completes the initialization. while (once->load(std::memory_order_acquire) == ONCE_STATE_EXECUTING_FUNCTION) { #ifdef _WIN32 ::Sleep(0); #else sched_yield(); #endif } } } } // namespace base } // namespace v8