question: public E poll ( ) { for ( ; ; ) { Node < E > h = head ; Node < E > t = tail ; Node < E > first = h . getPrev ( ) ; if ( h == head ) { if ( h != t ) { if ( first == null ) { fixList ( t , h ) ; continue ; } E item = first . getItem ( ) ; if ( casHead ( h , first ) ) { h . setNext ( null ) ; h . setPrev ( null ) ; count . decrementAndGet ( ) ; return item ; } } else { return null ; } } } }
target:  Dequeues an element from the queue. After a successful casHead, the prev and next pointers of the dequeued node are set to null to allow garbage collection.