yield() method

[Aarti Dahiya]

K&B book states that the yield() method may cause a running thread to back out if there are runnable threads of the SAME priority.
In one of the mock tests (don't remember which one), it states that the yield() method may cause a running thread to back out if there are runnable threads of the SAME OR HIGHER priority.

Which one is correct?

Thanks.

[Murtuza Akhtari]

If a new Thread with HIGHER priority enters the Runnable State....the thread scheduler will automatically pre-empt the running thread and put in the Higher priority thread in the Running state. If you happen to call yield()...at a moment when a HIgher priority thread enters the Runnable thread....the currently running thread could back out due to either of the reasons

Calling yield() or
Thread Scheduler

However tht precise timing of calling yield() is rare...so more often than not, yield() is used to back off a thread to offer CPU time to same priority threads

[Peter den Haan]

yield() will yield to a thread of higher priority as well of course.

Be careful when thinking in terms of pre-empting... JVMs do not necessarily use pre-emptive scheduling. In such cases some well-placed yield()s may be absolutely necessary to get the level of concurrency you need.

- Peter