>>750
atomic_int a = 0, b = 0;

//thread1
a.store_release(1);
int v = a.load_acquire();
int x = b.load_acquire();

//thread2
b.store_release(1);
int w = b.load_acquire();
int y = a.load_acquire();

のときでも x == 0 && y == 0 はありうる?