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
NeedsInstance()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
CompleteInstance(void * instance,void (* dtor)(void *))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