security/sandbox/chromium/base/lazy_instance.cc@6474c204b198 (annotated)
security/sandbox/chromium/base/lazy_instance.cc
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
| michael@0 | 1 | // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
| michael@0 | 2 | // Use of this source code is governed by a BSD-style license that can be |
| michael@0 | 3 | // found in the LICENSE file. |
| michael@0 | 4 | |
| michael@0 | 5 | #include "base/lazy_instance.h" |
| michael@0 | 6 | |
| michael@0 | 7 | #include "base/at_exit.h" |
| michael@0 | 8 | #include "base/atomicops.h" |
| michael@0 | 9 | #include "base/basictypes.h" |
| michael@0 | 10 | #include "base/threading/platform_thread.h" |
| michael@0 | 11 | #include "base/third_party/dynamic_annotations/dynamic_annotations.h" |
| michael@0 | 12 | |
| michael@0 | 13 | namespace base { |
| michael@0 | 14 | namespace internal { |
| michael@0 | 15 | |
| michael@0 | 16 | // TODO(joth): This function could be shared with Singleton, in place of its |
| michael@0 | 17 | // WaitForInstance() call. |
| michael@0 | 18 | bool NeedsLazyInstance(subtle::AtomicWord* state) { |
| michael@0 | 19 | // Try to create the instance, if we're the first, will go from 0 to |
| michael@0 | 20 | // kLazyInstanceStateCreating, otherwise we've already been beaten here. |
| michael@0 | 21 | // The memory access has no memory ordering as state 0 and |
| michael@0 | 22 | // kLazyInstanceStateCreating have no associated data (memory barriers are |
| michael@0 | 23 | // all about ordering of memory accesses to *associated* data). |
| michael@0 | 24 | if (subtle::NoBarrier_CompareAndSwap(state, 0, |
| michael@0 | 25 | kLazyInstanceStateCreating) == 0) |
| michael@0 | 26 | // Caller must create instance |
| michael@0 | 27 | return true; |
| michael@0 | 28 | |
| michael@0 | 29 | // It's either in the process of being created, or already created. Spin. |
| michael@0 | 30 | // The load has acquire memory ordering as a thread which sees |
| michael@0 | 31 | // state_ == STATE_CREATED needs to acquire visibility over |
| michael@0 | 32 | // the associated data (buf_). Pairing Release_Store is in |
| michael@0 | 33 | // CompleteLazyInstance(). |
| michael@0 | 34 | while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) { |
| michael@0 | 35 | PlatformThread::YieldCurrentThread(); |
| michael@0 | 36 | } |
| michael@0 | 37 | // Someone else created the instance. |
| michael@0 | 38 | return false; |
| michael@0 | 39 | } |
| michael@0 | 40 | |
| michael@0 | 41 | void CompleteLazyInstance(subtle::AtomicWord* state, |
| michael@0 | 42 | subtle::AtomicWord new_instance, |
| michael@0 | 43 | void* lazy_instance, |
| michael@0 | 44 | void (*dtor)(void*)) { |
| michael@0 | 45 | // See the comment to the corresponding HAPPENS_AFTER in Pointer(). |
| michael@0 | 46 | ANNOTATE_HAPPENS_BEFORE(state); |
| michael@0 | 47 | |
| michael@0 | 48 | // Instance is created, go from CREATING to CREATED. |
| michael@0 | 49 | // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's |
| michael@0 | 50 | // are in NeedsInstance() and Pointer(). |
| michael@0 | 51 | subtle::Release_Store(state, new_instance); |
| michael@0 | 52 | |
| michael@0 | 53 | // Make sure that the lazily instantiated object will get destroyed at exit. |
| michael@0 | 54 | if (dtor) |
| michael@0 | 55 | AtExitManager::RegisterCallback(dtor, lazy_instance); |
| michael@0 | 56 | } |
| michael@0 | 57 | |
| michael@0 | 58 | } // namespace internal |
| michael@0 | 59 | } // namespace base |
