Can you give a concrete example? Cache coherency is almost never the right thing to think about with shared memory concurrency. It's all about interleaving of

Can you give a concrete example? Cache coherency is almost never the right thing to think about with shared memory concurrency. It's all about interleaving of instruction execution and possible reordering of memory reads or writes. If by sleep(), you mean a spin loop, its possible that the compiler has reordered a write past an empty loop that appears to have no side effects. If you're talking about an OS API to delay execution, then sleep should allow other threads to see the writes done before the sleep. It's just not a great way to synchronize compared to a condition variable since sleep waits for some arbitrary amount of time rather than exactly as much as is needed to observe a change.