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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #include "base/lazy_instance.h" | 5 #include "base/lazy_instance.h" |
6 | 6 |
7 #include "base/at_exit.h" | 7 #include "base/at_exit.h" |
8 #include "base/atomicops.h" | 8 #include "base/atomicops.h" |
9 #include "base/basictypes.h" | 9 #include "base/basictypes.h" |
10 #include "base/threading/platform_thread.h" | 10 #include "base/threading/platform_thread.h" |
11 #include "base/third_party/dynamic_annotations/dynamic_annotations.h" | 11 #include "base/third_party/dynamic_annotations/dynamic_annotations.h" |
12 | 12 |
13 namespace base { | 13 namespace base { |
| 14 namespace internal { |
14 | 15 |
15 bool LazyInstanceHelper::NeedsInstance() { | 16 // TODO(joth): This function could be shared with Singleton, in place of its |
16 // Try to create the instance, if we're the first, will go from EMPTY | 17 // WaitForInstance() call. |
17 // to CREATING, otherwise we've already been beaten here. | 18 bool NeedsLazyInstance(subtle::AtomicWord* state) { |
18 // The memory access has no memory ordering as STATE_EMPTY and STATE_CREATING | 19 // Try to create the instance, if we're the first, will go from 0 to |
19 // has no associated data (memory barriers are all about ordering | 20 // kLazyInstanceStateCreating, otherwise we've already been beaten here. |
20 // of memory accesses to *associated* data). | 21 // The memory access has no memory ordering as state 0 and |
21 if (base::subtle::NoBarrier_CompareAndSwap( | 22 // kLazyInstanceStateCreating have no associated data (memory barriers are |
22 &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) | 23 // all about ordering of memory accesses to *associated* data). |
| 24 if (subtle::NoBarrier_CompareAndSwap(state, 0, |
| 25 kLazyInstanceStateCreating) == 0) |
23 // Caller must create instance | 26 // Caller must create instance |
24 return true; | 27 return true; |
25 | 28 |
26 // It's either in the process of being created, or already created. Spin. | 29 // It's either in the process of being created, or already created. Spin. |
27 // The load has acquire memory ordering as a thread which sees | 30 // The load has acquire memory ordering as a thread which sees |
28 // state_ == STATE_CREATED needs to acquire visibility over | 31 // state_ == STATE_CREATED needs to acquire visibility over |
29 // the associated data (buf_). Pairing Release_Store is in | 32 // the associated data (buf_). Pairing Release_Store is in |
30 // CompleteInstance(). | 33 // CompleteLazyInstance(). |
31 while (base::subtle::Acquire_Load(&state_) != STATE_CREATED) | 34 while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) { |
32 PlatformThread::YieldCurrentThread(); | 35 PlatformThread::YieldCurrentThread(); |
33 | 36 } |
34 // Someone else created the instance. | 37 // Someone else created the instance. |
35 return false; | 38 return false; |
36 } | 39 } |
37 | 40 |
38 void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) { | 41 void CompleteLazyInstance(subtle::AtomicWord* state, |
| 42 subtle::AtomicWord new_instance, |
| 43 void* lazy_instance, |
| 44 void (*dtor)(void*)) { |
39 // See the comment to the corresponding HAPPENS_AFTER in Pointer(). | 45 // See the comment to the corresponding HAPPENS_AFTER in Pointer(). |
40 ANNOTATE_HAPPENS_BEFORE(&state_); | 46 ANNOTATE_HAPPENS_BEFORE(state); |
41 | 47 |
42 // Instance is created, go from CREATING to CREATED. | 48 // Instance is created, go from CREATING to CREATED. |
43 // Releases visibility over buf_ to readers. Pairing Acquire_Load's are in | 49 // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's |
44 // NeedsInstance() and Pointer(). | 50 // are in NeedsInstance() and Pointer(). |
45 base::subtle::Release_Store(&state_, STATE_CREATED); | 51 subtle::Release_Store(state, new_instance); |
46 | 52 |
47 // Make sure that the lazily instantiated object will get destroyed at exit. | 53 // Make sure that the lazily instantiated object will get destroyed at exit. |
48 if (dtor) | 54 if (dtor) |
49 base::AtExitManager::RegisterCallback(dtor, instance); | 55 AtExitManager::RegisterCallback(dtor, lazy_instance); |
50 } | 56 } |
51 | 57 |
| 58 } // namespace internal |
52 } // namespace base | 59 } // namespace base |
53 | |
54 | |
55 | |
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