In addition to what plorkyeran said: While volatile alone doesn't synchronize accesses between threads, it is enough to ensure that the variable is read separat

In addition to what plorkyeran said: While volatile alone doesn't synchronize accesses between threads, it is enough to ensure that the variable is read separately in each iteration of the loop—though it might just be read from the L1 cache and not take into account writes from other cores.