atomic_sequence_num.h 1.7 KB
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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.

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#ifndef BUTIL_ATOMIC_SEQUENCE_NUM_H_
#define BUTIL_ATOMIC_SEQUENCE_NUM_H_
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#include "butil/atomicops.h"
#include "butil/basictypes.h"
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namespace butil {
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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>(
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        butil::subtle::NoBarrier_AtomicIncrement(&seq_, 1) - 1);
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  }

 private:
  friend class AtomicSequenceNumber;

  inline void Reset() {
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    butil::subtle::Release_Store(&seq_, 0);
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  }

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  butil::subtle::Atomic32 seq_;
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};

// 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);
};

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}  // namespace butil
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#endif  // BUTIL_ATOMIC_SEQUENCE_NUM_H_