michael@0: // Copyright (c) 2011 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #include "base/memory/singleton.h"
michael@0: #include "base/threading/platform_thread.h"
michael@0: 
michael@0: namespace base {
michael@0: namespace internal {
michael@0: 
michael@0: subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance) {
michael@0:   // Handle the race. Another thread beat us and either:
michael@0:   // - Has the object in BeingCreated state
michael@0:   // - Already has the object created...
michael@0:   // We know value != NULL.  It could be kBeingCreatedMarker, or a valid ptr.
michael@0:   // Unless your constructor can be very time consuming, it is very unlikely
michael@0:   // to hit this race.  When it does, we just spin and yield the thread until
michael@0:   // the object has been created.
michael@0:   subtle::AtomicWord value;
michael@0:   while (true) {
michael@0:     value = subtle::NoBarrier_Load(instance);
michael@0:     if (value != kBeingCreatedMarker)
michael@0:       break;
michael@0:     PlatformThread::YieldCurrentThread();
michael@0:   }
michael@0:   return value;
michael@0: }
michael@0: 
michael@0: }  // namespace internal
michael@0: }  // namespace base
michael@0: