--- jsr166/src/jsr166y/LinkedTransferQueue.java	2010/09/01 21:43:08	1.74
+++ jsr166/src/jsr166y/LinkedTransferQueue.java	2010/09/09 16:52:49	1.78
@@ -344,18 +344,18 @@ public class LinkedTransferQueue<E> exte
      * When these cases arise, rather than always retraversing the
      * entire list to find an actual predecessor to unlink (which
      * won't help for case (1) anyway), we record a conservative
-     * estimate of possible unsplice failures (in "sweepVotes").  We
-     * trigger a full sweep when the estimate exceeds a threshold
-     * indicating the maximum number of estimated removal failures to
-     * tolerate before sweeping through, unlinking cancelled nodes
-     * that were not unlinked upon initial removal. We perform sweeps
-     * by the thread hitting threshold (rather than background threads
-     * or by spreading work to other threads) because in the main
-     * contexts in which removal occurs, the caller is already
-     * timed-out, cancelled, or performing a potentially O(n)
-     * operation (i.e., remove(x)), none of which are time-critical
-     * enough to warrant the overhead that alternatives would impose
-     * on other threads.
+     * estimate of possible unsplice failures (in "sweepVotes").
+     * We trigger a full sweep when the estimate exceeds a threshold
+     * ("SWEEP_THRESHOLD") indicating the maximum number of estimated
+     * removal failures to tolerate before sweeping through, unlinking
+     * cancelled nodes that were not unlinked upon initial removal.
+     * We perform sweeps by the thread hitting threshold (rather than
+     * background threads or by spreading work to other threads)
+     * because in the main contexts in which removal occurs, the
+     * caller is already timed-out, cancelled, or performing a
+     * potentially O(n) operation (e.g. remove(x)), none of which are
+     * time-critical enough to warrant the overhead that alternatives
+     * would impose on other threads.
      *
      * Because the sweepVotes estimate is conservative, and because
      * nodes become unlinked "naturally" as they fall off the head of
@@ -428,8 +428,8 @@ public class LinkedTransferQueue<E> exte
         }
 
         /**
-         * Creates a new node. Uses relaxed write because item can only
-         * be seen if followed by CAS.
+         * Constructs a new node.  Uses relaxed write because item can
+         * only be seen after publication via casNext.
          */
         Node(Object item, boolean isData) {
             UNSAFE.putObject(this, itemOffset, item); // relaxed write
@@ -877,7 +877,8 @@ public class LinkedTransferQueue<E> exte
     }
 
     /**
-     * Unlinks matched nodes encountered in a traversal from head.
+     * Unlinks matched (typically cancelled) nodes encountered in a
+     * traversal from head.
      */
     private void sweep() {
         for (Node p = head, s, n; p != null && (s = p.next) != null; ) {
@@ -885,7 +886,7 @@ public class LinkedTransferQueue<E> exte
                 p = head;
             else if (!s.isMatched())
                 p = s;
-            else if ((n = s.next) == null) // trailing node is pinned
+            else if ((n = s.next) == null || s == n) // trailing node is pinned
                 break;
             else
                 p.casNext(s, n);