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src/java.base/share/classes/java/util/concurrent/ConcurrentLinkedDeque.java
changeset 47729 1563167c9520
parent 47340 83f933b97787
child 49433 b6671a111395
equal deleted inserted replaced
47728:0a65c8231efa 47729:1563167c9520 
   693      * Returns the predecessor of p, or the last node if p.prev has been
 
   693      * Returns the predecessor of p, or the last node if p.prev has been
 
   694      * linked to self, which will only be true if traversing with a
 
   694      * linked to self, which will only be true if traversing with a
 
   695      * stale pointer that is now off the list.
 
   695      * stale pointer that is now off the list.
 
   696      */
 
   696      */
 
   697     final Node<E> pred(Node<E> p) {
 
   697     final Node<E> pred(Node<E> p) {
 
   698         Node<E> q = p.prev;
 
   698         if (p == (p = p.prev))
 
   699         return (p == q) ? last() : q;
 
   699             p = last();
 
       
   700         return p;
 
   700     }
 
   701     }
 
   701 
   702 
   702     /**
 
   703     /**
 
   703      * Returns the first node, the unique node p for which:
 
   704      * Returns the first node, the unique node p for which:
 
   704      *     p.prev == null && p.next != p
 
   705      *     p.prev == null && p.next != p
 
   865         return true;
 
   866         return true;
 
   866     }
 
   867     }
 
   867 
   868 
   868     public E peekFirst() {
 
   869     public E peekFirst() {
 
   869         restart: for (;;) {
 
   870         restart: for (;;) {
 
   870             for (Node<E> first = first(), p = first;;) {
 
   871             E item;
 
   871                 final E item;
 
   872             Node<E> first = first(), p = first;
 
   872                 if ((item = p.item) != null) {
 
   873             while ((item = p.item) == null) {
 
   873                     // recheck for linearizability
 
   874                 if (p == (p = p.next)) continue restart;
 
   874                     if (first.prev != null) continue restart;
 
   875                 if (p == null)
 
   875                     return item;
 
   876                     break;
 
   876                 }
 
   877             }
 
   877                 if ((p = succ(p)) == null)
 
   878             // recheck for linearizability
 
   878                     return null;
 
   879             if (first.prev != null) continue restart;
 
   879             }
 
   880             return item;
 
   880         }
 
   881         }
 
   881     }
 
   882     }
 
   882 
   883 
   883     public E peekLast() {
 
   884     public E peekLast() {
 
   884         restart: for (;;) {
 
   885         restart: for (;;) {
 
   885             for (Node<E> last = last(), p = last;;) {
 
   886             E item;
 
   886                 final E item;
 
   887             Node<E> last = last(), p = last;
 
   887                 if ((item = p.item) != null) {
 
   888             while ((item = p.item) == null) {
 
   888                     // recheck for linearizability
 
   889                 if (p == (p = p.prev)) continue restart;
 
   889                     if (last.next != null) continue restart;
 
   890                 if (p == null)
 
   890                     return item;
 
   891                     break;
 
   891                 }
 
   892             }
 
   892                 if ((p = pred(p)) == null)
 
   893             // recheck for linearizability
 
   893                     return null;
 
   894             if (last.next != null) continue restart;
 
   894             }
 
   895             return item;
 
   895         }
 
   896         }
 
   896     }
 
   897     }
 
   897 
   898 
   898     /**
 
   899     /**
 
   899      * @throws NoSuchElementException {@inheritDoc}
 
   900      * @throws NoSuchElementException {@inheritDoc}
 
   919                     if (ITEM.compareAndSet(p, item, null)) {
 
   920                     if (ITEM.compareAndSet(p, item, null)) {
 
   920                         unlink(p);
 
   921                         unlink(p);
 
   921                         return item;
 
   922                         return item;
 
   922                     }
 
   923                     }
 
   923                 }
 
   924                 }
 
   924                 if ((p = succ(p)) == null)
 
   925                 if (p == (p = p.next)) continue restart;
 
       
   926                 if (p == null) {
 
       
   927                     if (first.prev != null) continue restart;
 
   925                     return null;
 
   928                     return null;
 
       
   929                 }
 
   926             }
 
   930             }
 
   927         }
 
   931         }
 
   928     }
 
   932     }
 
   929 
   933 
   930     public E pollLast() {
 
   934     public E pollLast() {
 
   937                     if (ITEM.compareAndSet(p, item, null)) {
 
   941                     if (ITEM.compareAndSet(p, item, null)) {
 
   938                         unlink(p);
 
   942                         unlink(p);
 
   939                         return item;
 
   943                         return item;
 
   940                     }
 
   944                     }
 
   941                 }
 
   945                 }
 
   942                 if ((p = pred(p)) == null)
 
   946                 if (p == (p = p.prev)) continue restart;
 
       
   947                 if (p == null) {
 
       
   948                     if (last.next != null) continue restart;
 
   943                     return null;
 
   949                     return null;
 
       
   950                 }
 
   944             }
 
   951             }
 
   945         }
 
   952         }
 
   946     }
 
   953     }
 
   947 
   954 
   948     /**
 
   955     /**
jdk-sandbox