5 typedef struct seqlock {
6 // Sequence for reader consistency check
8 // It needs to be atomic to avoid data races
12 atomic_init(&_seq, 0);
13 atomic_init(&_data, 0);
18 int old_seq = _seq.load(memory_order_acquire); // acquire
19 if (old_seq % 2 == 1) continue;
21 int res = _data.load(memory_order_acquire);
22 if (_seq.load(memory_order_relaxed) == old_seq) { // relaxed
28 void write(int new_data) {
30 // #1: either here or #2 must be acquire
31 int old_seq = _seq.load(memory_order_acquire); // acquire
32 // This might be a relaxed too
37 if (_seq.compare_exchange_strong(old_seq, old_seq + 1,
38 memory_order_relaxed, memory_order_relaxed))
43 _data.store(new_data, memory_order_release); // Can be relaxed
45 _seq.fetch_add(1, memory_order_release); // release