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