When running under a preemptive thread scheduling policy, a thread does not give up its processor unless blocked by a synchronization mechanism or preempted by a higher priority thread. If a thread executing under this scheduling policy does not block, no other threads of the same or lesser priority get a chance to execute on the processor.

Yield can be used in this situation to give other threads of the same priority a chance to execute. A thread that yields is usually moved to the end of its current priority queue and does not get a chance to execute again until all other threads of the same priority have had a chance.

A yield operation does not force a thread to give up the processor if no other threads of the same priority are currently eligible for execution. A yield in this situation has no affect on the scheduling of the thread.