michael@0: // Copyright (c) 2008 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/lazy_instance.h"
michael@0: 
michael@0: #include "base/at_exit.h"
michael@0: #include "base/atomicops.h"
michael@0: #include "base/basictypes.h"
michael@0: #include "base/platform_thread.h"
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: void LazyInstanceHelper::EnsureInstance(void* instance,
michael@0:                                         void (*ctor)(void*),
michael@0:                                         void (*dtor)(void*)) {
michael@0:   // Try to create the instance, if we're the first, will go from EMPTY
michael@0:   // to CREATING, otherwise we've already been beaten here.
michael@0:   if (base::subtle::Acquire_CompareAndSwap(
michael@0:           &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {
michael@0:     // Created the instance in the space provided by |instance|.
michael@0:     ctor(instance);
michael@0:     // Instance is created, go from CREATING to CREATED.
michael@0:     base::subtle::Release_Store(&state_, STATE_CREATED);
michael@0:     // Register the destructor callback with AtExitManager.
michael@0:     base::AtExitManager::RegisterCallback(dtor, instance);
michael@0:   } else {
michael@0:     // It's either in the process of being created, or already created.  Spin.
michael@0:     while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
michael@0:       PlatformThread::YieldCurrentThread();
michael@0:   }
michael@0: }
michael@0: 
michael@0: }  // namespace base