1 // Copyright 2012 The Chromium Authors 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 namespace base { 11 12 // AtomicSequenceNumber is a thread safe increasing sequence number generator. 13 // Its constructor doesn't emit a static initializer, so it's safe to use as a 14 // global variable or static member. 15 class AtomicSequenceNumber { 16 public: 17 constexpr AtomicSequenceNumber() = default; 18 AtomicSequenceNumber(const AtomicSequenceNumber&) = delete; 19 AtomicSequenceNumber& operator=(const AtomicSequenceNumber&) = delete; 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 29 } // namespace base 30 31 #endif // BASE_ATOMIC_SEQUENCE_NUM_H_ 32