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// Copyright 2013 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 "content/common/one_writer_seqlock.h"
namespace content {
OneWriterSeqLock::OneWriterSeqLock()
: sequence_(0) {
}
base::subtle::Atomic32 OneWriterSeqLock::ReadBegin() {
base::subtle::Atomic32 version;
for (;;) {
version = base::subtle::NoBarrier_Load(&sequence_);
// If the counter is even, then the associated data might be in a
// consistent state, so we can try to read.
if ((version & 1) == 0)
break;
// Otherwise, the writer is in the middle of an update. Retry the read.
base::PlatformThread::YieldCurrentThread();
}
return version;
}
bool OneWriterSeqLock::ReadRetry(base::subtle::Atomic32 version) {
// If the sequence number was updated then a read should be re-attempted.
// -- Load fence, read membarrier
return base::subtle::Release_Load(&sequence_) != version;
}
void OneWriterSeqLock::WriteBegin() {
// Increment the sequence number to odd to indicate the beginning of a write
// update.
base::subtle::Barrier_AtomicIncrement(&sequence_, 1);
// -- Store fence, write membarrier
}
void OneWriterSeqLock::WriteEnd() {
// Increment the sequence to an even number to indicate the completion of
// a write update.
// -- Store fence, write membarrier
base::subtle::Barrier_AtomicIncrement(&sequence_, 1);
}
} // namespace content
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