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
13 namespace base {
14
EnsureInstance(void * instance,void (* ctor)(void *),void (* dtor)(void *))15 void 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
ResetState(void * helper)47 void LazyInstanceHelper::ResetState(void* helper) {
48 reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
49 }
50
51 } // namespace base
52