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. 4 5 #ifndef BASE_ATOMIC_SEQUENCE_NUM_H_ 6 #define BASE_ATOMIC_SEQUENCE_NUM_H_ 7 8 #include "base/atomicops.h" 9 #include "base/macros.h" 10 11 namespace base { 12 13 class AtomicSequenceNumber; 14 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 21 // declared below. 22 class StaticAtomicSequenceNumber { 23 public: 24 inline int GetNext() { 25 return static_cast<int>( 26 base::subtle::NoBarrier_AtomicIncrement(&seq_, 1) - 1); 27 } 28 29 private: 30 friend class AtomicSequenceNumber; 31 32 inline void Reset() { 33 base::subtle::Release_Store(&seq_, 0); 34 } 35 36 base::subtle::Atomic32 seq_; 37 }; 38 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 { 44 public: 45 AtomicSequenceNumber() { 46 seq_.Reset(); 47 } 48 49 inline int GetNext() { 50 return seq_.GetNext(); 51 } 52 53 private: 54 StaticAtomicSequenceNumber seq_; 55 DISALLOW_COPY_AND_ASSIGN(AtomicSequenceNumber); 56 }; 57 58 } // namespace base 59 60 #endif // BASE_ATOMIC_SEQUENCE_NUM_H_ 61
