// Copyright 2012 the V8 project authors. All rights reserved. // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following // disclaimer in the documentation and/or other materials provided // with the distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived // from this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #include "once.h" #ifdef _WIN32 #include <windows.h> #else #include <sched.h> #endif #include "atomicops.h" #include "checks.h" namespace v8 { namespace internal { void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) { AtomicWord state = Acquire_Load(once); // Fast path. The provided function was already executed. if (state == 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. state = Acquire_CompareAndSwap( once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION); if (state == ONCE_STATE_UNINITIALIZED) { // We are the first thread to call this function, so we have to call the // function. init_func(arg); Release_Store(once, ONCE_STATE_DONE); } else { // Another thread has already started executing the function. We need to // wait until it completes the initialization. while (state == ONCE_STATE_EXECUTING_FUNCTION) { #ifdef _WIN32 ::Sleep(0); #else sched_yield(); #endif state = Acquire_Load(once); } } } } } // namespace v8::internal