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35 lines
1.2 KiB
C++
35 lines
1.2 KiB
C++
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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/memory/singleton.h"
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#include "base/threading/platform_thread.h"
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namespace base {
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namespace internal {
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subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance) {
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// Handle the race. Another thread beat us and either:
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// - Has the object in BeingCreated state
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// - Already has the object created...
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// We know value != NULL. It could be kBeingCreatedMarker, or a valid ptr.
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// Unless your constructor can be very time consuming, it is very unlikely
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// to hit this race. When it does, we just spin and yield the thread until
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// the object has been created.
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subtle::AtomicWord value;
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while (true) {
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// The load has acquire memory ordering as the thread which reads the
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// instance pointer must acquire visibility over the associated data.
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// The pairing Release_Store operation is in Singleton::get().
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value = subtle::Acquire_Load(instance);
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if (value != kBeingCreatedMarker)
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break;
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PlatformThread::YieldCurrentThread();
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}
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return value;
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}
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} // namespace internal
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} // namespace base
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