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// Copyright (c) 2012 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.
#ifndef BASE_ATOMIC_SEQUENCE_NUM_H_
#define BASE_ATOMIC_SEQUENCE_NUM_H_
#include "base/atomicops.h"
#include "base/macros.h"
namespace base {
class AtomicSequenceNumber;
// Static (POD) AtomicSequenceNumber that MUST be used in global scope (or
// non-function scope) ONLY. This implementation does not generate any static
// initializer. Note that it does not implement any constructor which means
// that its fields are not initialized except when it is stored in the global
// data section (.data in ELF). If you want to allocate an atomic sequence
// number on the stack (or heap), please use the AtomicSequenceNumber class
// declared below.
class StaticAtomicSequenceNumber {
public:
inline int GetNext() {
return static_cast<int>(
base::subtle::NoBarrier_AtomicIncrement(&seq_, 1) - 1);
}
private:
friend class AtomicSequenceNumber;
inline void Reset() {
base::subtle::Release_Store(&seq_, 0);
}
base::subtle::Atomic32 seq_;
};
// AtomicSequenceNumber that can be stored and used safely (i.e. its fields are
// always initialized as opposed to StaticAtomicSequenceNumber declared above).
// Please use StaticAtomicSequenceNumber if you want to declare an atomic
// sequence number in the global scope.
class AtomicSequenceNumber {
public:
AtomicSequenceNumber() {
seq_.Reset();
}
inline int GetNext() {
return seq_.GetNext();
}
private:
StaticAtomicSequenceNumber seq_;
DISALLOW_COPY_AND_ASSIGN(AtomicSequenceNumber);
};
} // namespace base
#endif // BASE_ATOMIC_SEQUENCE_NUM_H_
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