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author | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
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committer | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
commit | 5f8de423f190bbb79a62f804151bc24824fa32d8 (patch) | |
tree | 10027f336435511475e392454359edea8e25895d /security/sandbox/chromium/base/lazy_instance.cc | |
parent | 49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff) | |
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Add m-esr52 at 52.6.0
Diffstat (limited to 'security/sandbox/chromium/base/lazy_instance.cc')
-rw-r--r-- | security/sandbox/chromium/base/lazy_instance.cc | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/lazy_instance.cc b/security/sandbox/chromium/base/lazy_instance.cc new file mode 100644 index 000000000..54680655a --- /dev/null +++ b/security/sandbox/chromium/base/lazy_instance.cc @@ -0,0 +1,54 @@ +// Copyright (c) 2011 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#include "base/lazy_instance.h" + +#include "base/at_exit.h" +#include "base/atomicops.h" +#include "base/threading/platform_thread.h" + +namespace base { +namespace internal { + +// TODO(joth): This function could be shared with Singleton, in place of its +// WaitForInstance() call. +bool NeedsLazyInstance(subtle::AtomicWord* state) { + // Try to create the instance, if we're the first, will go from 0 to + // kLazyInstanceStateCreating, otherwise we've already been beaten here. + // The memory access has no memory ordering as state 0 and + // kLazyInstanceStateCreating have no associated data (memory barriers are + // all about ordering of memory accesses to *associated* data). + if (subtle::NoBarrier_CompareAndSwap(state, 0, + kLazyInstanceStateCreating) == 0) + // Caller must create instance + return true; + + // It's either in the process of being created, or already created. Spin. + // The load has acquire memory ordering as a thread which sees + // state_ == STATE_CREATED needs to acquire visibility over + // the associated data (buf_). Pairing Release_Store is in + // CompleteLazyInstance(). + while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) { + PlatformThread::YieldCurrentThread(); + } + // Someone else created the instance. + return false; +} + +void CompleteLazyInstance(subtle::AtomicWord* state, + subtle::AtomicWord new_instance, + void* lazy_instance, + void (*dtor)(void*)) { + // Instance is created, go from CREATING to CREATED. + // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's + // are in NeedsInstance() and Pointer(). + subtle::Release_Store(state, new_instance); + + // Make sure that the lazily instantiated object will get destroyed at exit. + if (dtor) + AtExitManager::RegisterCallback(dtor, lazy_instance); +} + +} // namespace internal +} // namespace base |