reduce lock contention in bulk_queue.
reduce lock contention in bulk_queue.

silky/FlashGraph,icoming/FlashGraph,icoming/FlashX,silky/FlashGraph,zheng-da/FlashX,flashxio/FlashX,flashxio/FlashX,silky/FlashGraph,zheng-da/FlashX,zheng-da/FlashX,flashxio/FlashX,icoming/FlashGraph,icoming/FlashX,icoming/FlashX,icoming/FlashGraph,zheng-da/FlashX,flashxio/FlashX,icoming/FlashGraph,icoming/FlashGraph,silky/FlashGraph,icoming/FlashX,flashxio/FlashX,zheng-da/FlashX,flashxio/FlashX,silky/FlashGraph,icoming/FlashX