1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BASE_ATOMIC_SEQUENCE_NUM_H_
6 #define BASE_ATOMIC_SEQUENCE_NUM_H_
8 #include "base/atomicops.h"
9 #include "base/basictypes.h"
13 class AtomicSequenceNumber;
15 // Static (POD) AtomicSequenceNumber that MUST be used in global scope (or
16 // non-function scope) ONLY. This implementation does not generate any static
17 // initializer. Note that it does not implement any constructor which means
18 // that its fields are not initialized except when it is stored in the global
19 // data section (.data in ELF). If you want to allocate an atomic sequence
20 // number on the stack (or heap), please use the AtomicSequenceNumber class
22 class StaticAtomicSequenceNumber {
24 inline int GetNext() {
25 return static_cast<int>(
26 base::subtle::NoBarrier_AtomicIncrement(&seq_, 1) - 1);
30 friend class AtomicSequenceNumber;
33 base::subtle::Release_Store(&seq_, 0);
36 base::subtle::Atomic32 seq_;
39 // AtomicSequenceNumber that can be stored and used safely (i.e. its fields are
40 // always initialized as opposed to StaticAtomicSequenceNumber declared above).
41 // Please use StaticAtomicSequenceNumber if you want to declare an atomic
42 // sequence number in the global scope.
43 class AtomicSequenceNumber {
45 AtomicSequenceNumber() {
49 inline int GetNext() {
50 return seq_.GetNext();
54 StaticAtomicSequenceNumber seq_;
55 DISALLOW_COPY_AND_ASSIGN(AtomicSequenceNumber);
60 #endif // BASE_ATOMIC_SEQUENCE_NUM_H_