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 <atomic> 9 10 #include "base/macros.h" 11 12 namespace base { 13 14 // AtomicSequenceNumber is a thread safe increasing sequence number generator. 15 // Its constructor doesn't emit a static initializer, so it's safe to use as a 16 // global variable or static member. 17 class AtomicSequenceNumber { 18 public: 19 constexpr AtomicSequenceNumber() = default; 20 21 // Returns an increasing sequence number starts from 0 for each call. 22 // This function can be called from any thread without data race. GetNext()23 inline int GetNext() { return seq_.fetch_add(1, std::memory_order_relaxed); } 24 25 private: 26 std::atomic_int seq_{0}; 27 28 DISALLOW_COPY_AND_ASSIGN(AtomicSequenceNumber); 29 }; 30 31 } // namespace base 32 33 #endif // BASE_ATOMIC_SEQUENCE_NUM_H_ 34