1 // Copyright (c) 2010 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/lazy_instance.h" 6 7 #include "base/at_exit.h" 8 #include "base/atomicops.h" 9 #include "base/basictypes.h" 10 #include "base/threading/platform_thread.h" 11 #include "base/third_party/dynamic_annotations/dynamic_annotations.h" 12 13 namespace base { 14 15 bool LazyInstanceHelper::NeedsInstance() { 16 // Try to create the instance, if we're the first, will go from EMPTY 17 // to CREATING, otherwise we've already been beaten here. 18 if (base::subtle::Acquire_CompareAndSwap( 19 &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) { 20 // Caller must create instance 21 return true; 22 } else { 23 // It's either in the process of being created, or already created. Spin. 24 while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) 25 PlatformThread::YieldCurrentThread(); 26 } 27 28 // Someone else created the instance. 29 return false; 30 } 31 32 void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) { 33 // See the comment to the corresponding HAPPENS_AFTER in Pointer(). 34 ANNOTATE_HAPPENS_BEFORE(&state_); 35 36 // Instance is created, go from CREATING to CREATED. 37 base::subtle::Release_Store(&state_, STATE_CREATED); 38 39 // Make sure that the lazily instantiated object will get destroyed at exit. 40 if (dtor) 41 base::AtExitManager::RegisterCallback(dtor, instance); 42 } 43 44 } // namespace base 45
