1 // Copyright (c) 2011 The Chromium 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 "base/memory/singleton.h" 6 #include "base/threading/platform_thread.h" 7 8 namespace base { 9 namespace internal { 10 11 subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance) { 12 // Handle the race. Another thread beat us and either: 13 // - Has the object in BeingCreated state 14 // - Already has the object created... 15 // We know value != NULL. It could be kBeingCreatedMarker, or a valid ptr. 16 // Unless your constructor can be very time consuming, it is very unlikely 17 // to hit this race. When it does, we just spin and yield the thread until 18 // the object has been created. 19 subtle::AtomicWord value; 20 while (true) { 21 // The load has acquire memory ordering as the thread which reads the 22 // instance pointer must acquire visibility over the associated data. 23 // The pairing Release_Store operation is in Singleton::get(). 24 value = subtle::Acquire_Load(instance); 25 if (value != kBeingCreatedMarker) 26 break; 27 PlatformThread::YieldCurrentThread(); 28 } 29 return value; 30 } 31 32 } // namespace internal 33 } // namespace base 34 35
