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comparison: security/sandbox/chromium/base/lazy_instance.cc
security/sandbox/chromium/base/lazy_instance.cc
- branch
- TOR_BUG_9701
- changeset 14
- 925c144e1f1f
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| -1:000000000000 | 0:3417626e55e7 |
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| 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 | |
| 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 namespace internal { | |
| 15 | |
| 16 // TODO(joth): This function could be shared with Singleton, in place of its | |
| 17 // WaitForInstance() call. | |
| 18 bool NeedsLazyInstance(subtle::AtomicWord* state) { | |
| 19 // Try to create the instance, if we're the first, will go from 0 to | |
| 20 // kLazyInstanceStateCreating, otherwise we've already been beaten here. | |
| 21 // The memory access has no memory ordering as state 0 and | |
| 22 // kLazyInstanceStateCreating have no associated data (memory barriers are | |
| 23 // all about ordering of memory accesses to *associated* data). | |
| 24 if (subtle::NoBarrier_CompareAndSwap(state, 0, | |
| 25 kLazyInstanceStateCreating) == 0) | |
| 26 // Caller must create instance | |
| 27 return true; | |
| 28 | |
| 29 // It's either in the process of being created, or already created. Spin. | |
| 30 // The load has acquire memory ordering as a thread which sees | |
| 31 // state_ == STATE_CREATED needs to acquire visibility over | |
| 32 // the associated data (buf_). Pairing Release_Store is in | |
| 33 // CompleteLazyInstance(). | |
| 34 while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) { | |
| 35 PlatformThread::YieldCurrentThread(); | |
| 36 } | |
| 37 // Someone else created the instance. | |
| 38 return false; | |
| 39 } | |
| 40 | |
| 41 void CompleteLazyInstance(subtle::AtomicWord* state, | |
| 42 subtle::AtomicWord new_instance, | |
| 43 void* lazy_instance, | |
| 44 void (*dtor)(void*)) { | |
| 45 // See the comment to the corresponding HAPPENS_AFTER in Pointer(). | |
| 46 ANNOTATE_HAPPENS_BEFORE(state); | |
| 47 | |
| 48 // Instance is created, go from CREATING to CREATED. | |
| 49 // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's | |
| 50 // are in NeedsInstance() and Pointer(). | |
| 51 subtle::Release_Store(state, new_instance); | |
| 52 | |
| 53 // Make sure that the lazily instantiated object will get destroyed at exit. | |
| 54 if (dtor) | |
| 55 AtExitManager::RegisterCallback(dtor, lazy_instance); | |
| 56 } | |
| 57 | |
| 58 } // namespace internal | |
| 59 } // namespace base |
