/**
* Returns the next job or releases a job slot. If a non-null value is returned, the caller must
* submit the job to execution. Should only be caller by a caller than currently holds a job slot.
*
* @return
*/
private synchronized PrioritizedRequest nextOrRelease() {
PrioritizedRequest request = _queue.poll();
if (request == null) {
_semaphore.release();
}
return request;
}
