| // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "base/lazy_instance.h" |
| |
| #include "base/at_exit.h" |
| #include "base/atomicops.h" |
| #include "base/basictypes.h" |
| #include "base/threading/platform_thread.h" |
| #include "base/third_party/dynamic_annotations/dynamic_annotations.h" |
| |
| namespace base { |
| |
| bool LazyInstanceHelper::NeedsInstance() { |
| // Try to create the instance, if we're the first, will go from EMPTY |
| // to CREATING, otherwise we've already been beaten here. |
| // The memory access has no memory ordering as STATE_EMPTY and STATE_CREATING |
| // has no associated data (memory barriers are all about ordering |
| // of memory accesses to *associated* data). |
| if (base::subtle::NoBarrier_CompareAndSwap( |
| &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) |
| // Caller must create instance |
| return true; |
| |
| // It's either in the process of being created, or already created. Spin. |
| // The load has acquire memory ordering as a thread which sees |
| // state_ == STATE_CREATED needs to acquire visibility over |
| // the associated data (buf_). Pairing Release_Store is in |
| // CompleteInstance(). |
| while (base::subtle::Acquire_Load(&state_) != STATE_CREATED) |
| PlatformThread::YieldCurrentThread(); |
| |
| // Someone else created the instance. |
| return false; |
| } |
| |
| void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) { |
| // See the comment to the corresponding HAPPENS_AFTER in Pointer(). |
| ANNOTATE_HAPPENS_BEFORE(&state_); |
| |
| // Instance is created, go from CREATING to CREATED. |
| // Releases visibility over buf_ to readers. Pairing Acquire_Load's are in |
| // NeedsInstance() and Pointer(). |
| base::subtle::Release_Store(&state_, STATE_CREATED); |
| |
| // Make sure that the lazily instantiated object will get destroyed at exit. |
| if (dtor) |
| base::AtExitManager::RegisterCallback(dtor, instance); |
| } |
| |
| } // namespace base |
| |
| |
| |