- * Unless otherwise stated, the caller must ensure mutual exclusion of
- * queue update operations "dequeue" and "splice" (for source queue).
- * Queue read operations "first" and "next", which are used by
- * "for_each" iterations, need to be protected against concurrent
- * "dequeue" and "splice" (for source queue) by the caller.
- * "enqueue", "splice" (for destination queue), and "empty" are the only
- * operations that can be used without any mutual exclusion.