lazy_instance.cc revision c7f5f8508d98d5952d42ed7648c2a8f30a4da156 
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/dynamic_annotations.h"
10#include "base/basictypes.h"
11#include "base/platform_thread.h"
12
13namespace base {
14
15void LazyInstanceHelper::EnsureInstance(void* instance,
16                                        void (*ctor)(void*),
17                                        void (*dtor)(void*)) {
18  // Try to create the instance, if we're the first, will go from EMPTY
19  // to CREATING, otherwise we've already been beaten here.
20  if (base::subtle::Acquire_CompareAndSwap(
21          &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {
22    // Created the instance in the space provided by |instance|.
23    ctor(instance);
24
25    // See the comment to the corresponding HAPPENS_AFTER in Pointer().
26    ANNOTATE_HAPPENS_BEFORE(&state_);
27
28    // Instance is created, go from CREATING to CREATED.
29    base::subtle::Release_Store(&state_, STATE_CREATED);
30
31    // Allow reusing the LazyInstance (reset it to the initial state). This
32    // makes possible calling all AtExit callbacks between tests. Assumes that
33    // no other threads execute when AtExit callbacks are processed.
34    base::AtExitManager::RegisterCallback(&LazyInstanceHelper::ResetState,
35                                          this);
36
37    // Make sure that the lazily instantiated object will get destroyed at exit.
38    base::AtExitManager::RegisterCallback(dtor, instance);
39  } else {
40    // It's either in the process of being created, or already created.  Spin.
41    while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
42      PlatformThread::YieldCurrentThread();
43  }
44}
45
46// static
47void LazyInstanceHelper::ResetState(void* helper) {
48  reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
49}
50
51}  // namespace base
52