* "enqueue", "splice" (for destination queue), and "empty" are the only
* operations that can be used without any mutual exclusion.
* Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
*
* For convenience, cds_wfcq_dequeue_blocking() and
* cds_wfcq_splice_blocking() hold the dequeue lock.
* "enqueue", "splice" (for destination queue), and "empty" are the only
* operations that can be used without any mutual exclusion.
* Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
*
* For convenience, cds_wfcq_dequeue_blocking() and
* cds_wfcq_splice_blocking() hold the dequeue lock.