xref: /aosp_15_r20/external/libchrome/base/atomic_sequence_num.h (revision 635a864187cb8b6c713ff48b7e790a6b21769273)
1*635a8641SAndroid Build Coastguard Worker // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2*635a8641SAndroid Build Coastguard Worker // Use of this source code is governed by a BSD-style license that can be
3*635a8641SAndroid Build Coastguard Worker // found in the LICENSE file.
4*635a8641SAndroid Build Coastguard Worker 
5*635a8641SAndroid Build Coastguard Worker #ifndef BASE_ATOMIC_SEQUENCE_NUM_H_
6*635a8641SAndroid Build Coastguard Worker #define BASE_ATOMIC_SEQUENCE_NUM_H_
7*635a8641SAndroid Build Coastguard Worker 
8*635a8641SAndroid Build Coastguard Worker #include <atomic>
9*635a8641SAndroid Build Coastguard Worker 
10*635a8641SAndroid Build Coastguard Worker #include "base/macros.h"
11*635a8641SAndroid Build Coastguard Worker 
12*635a8641SAndroid Build Coastguard Worker namespace base {
13*635a8641SAndroid Build Coastguard Worker 
14*635a8641SAndroid Build Coastguard Worker // AtomicSequenceNumber is a thread safe increasing sequence number generator.
15*635a8641SAndroid Build Coastguard Worker // Its constructor doesn't emit a static initializer, so it's safe to use as a
16*635a8641SAndroid Build Coastguard Worker // global variable or static member.
17*635a8641SAndroid Build Coastguard Worker class AtomicSequenceNumber {
18*635a8641SAndroid Build Coastguard Worker  public:
19*635a8641SAndroid Build Coastguard Worker   constexpr AtomicSequenceNumber() = default;
20*635a8641SAndroid Build Coastguard Worker 
21*635a8641SAndroid Build Coastguard Worker   // Returns an increasing sequence number starts from 0 for each call.
22*635a8641SAndroid Build Coastguard Worker   // This function can be called from any thread without data race.
GetNext()23*635a8641SAndroid Build Coastguard Worker   inline int GetNext() { return seq_.fetch_add(1, std::memory_order_relaxed); }
24*635a8641SAndroid Build Coastguard Worker 
25*635a8641SAndroid Build Coastguard Worker  private:
26*635a8641SAndroid Build Coastguard Worker   std::atomic_int seq_{0};
27*635a8641SAndroid Build Coastguard Worker 
28*635a8641SAndroid Build Coastguard Worker   DISALLOW_COPY_AND_ASSIGN(AtomicSequenceNumber);
29*635a8641SAndroid Build Coastguard Worker };
30*635a8641SAndroid Build Coastguard Worker 
31*635a8641SAndroid Build Coastguard Worker }  // namespace base
32*635a8641SAndroid Build Coastguard Worker 
33*635a8641SAndroid Build Coastguard Worker #endif  // BASE_ATOMIC_SEQUENCE_NUM_H_
34