lazy_instance.cc revision 3345a6884c488ff3a535c2c9acdd33d74b37e311 
1// Copyright (c) 2008 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/platform_thread.h"
11#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
12
13namespace base {
14
15bool 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
32void 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  base::AtExitManager::RegisterCallback(dtor, instance);
41}
42
43}  // namespace base
44