--- jsr166/src/jsr166y/LinkedTransferQueue.java	2008/11/16 20:24:54	1.9
+++ jsr166/src/jsr166y/LinkedTransferQueue.java	2009/07/24 23:48:26	1.25
@@ -10,8 +10,6 @@ import java.util.concurrent.locks.*;
 import java.util.concurrent.atomic.*;
 import java.util.*;
 import java.io.*;
-import sun.misc.Unsafe;
-import java.lang.reflect.*;
 
 /**
  * An unbounded {@linkplain TransferQueue} based on linked nodes.
@@ -21,7 +19,7 @@ import java.lang.reflect.*;
  * producer.  The <em>tail</em> of the queue is that element that has
  * been on the queue the shortest time for some producer.
  *
- * <p>Beware that, unlike in most collections, the <tt>size</tt>
+ * <p>Beware that, unlike in most collections, the {@code size}
  * method is <em>NOT</em> a constant-time operation. Because of the
  * asynchronous nature of these queues, determining the current number
  * of elements requires a traversal of the elements.
@@ -44,7 +42,6 @@ import java.lang.reflect.*;
  * @since 1.7
  * @author Doug Lea
  * @param <E> the type of elements held in this collection
- *
  */
 public class LinkedTransferQueue<E> extends AbstractQueue<E>
     implements TransferQueue<E>, java.io.Serializable {
@@ -81,7 +78,7 @@ public class LinkedTransferQueue<E> exte
      * seems not to vary with number of CPUs (beyond 2) so is just
      * a constant.
      */
-    static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
+    static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32;
 
     /**
      * The number of times to spin before blocking in untimed waits.
@@ -103,22 +100,30 @@ public class LinkedTransferQueue<E> exte
      * garbage retention. Similarly, setting the next field to this is
      * used as sentinel that node is off list.
      */
-    static final class QNode extends AtomicReference<Object> {
-        volatile QNode next;
+    static final class Node<E> extends AtomicReference<Object> {
+        volatile Node<E> next;
         volatile Thread waiter;       // to control park/unpark
         final boolean isData;
-        QNode(Object item, boolean isData) {
+
+        Node(E item, boolean isData) {
             super(item);
             this.isData = isData;
         }
 
-        static final AtomicReferenceFieldUpdater<QNode, QNode>
+        @SuppressWarnings("rawtypes")
+        static final AtomicReferenceFieldUpdater<Node, Node>
             nextUpdater = AtomicReferenceFieldUpdater.newUpdater
-            (QNode.class, QNode.class, "next");
+            (Node.class, Node.class, "next");
 
-        boolean casNext(QNode cmp, QNode val) {
+        final boolean casNext(Node<E> cmp, Node<E> val) {
             return nextUpdater.compareAndSet(this, cmp, val);
         }
+
+        final void clearNext() {
+            nextUpdater.lazySet(this, this);
+        }
+
+        private static final long serialVersionUID = -3375979862319811754L;
     }
 
     /**
@@ -130,28 +135,30 @@ public class LinkedTransferQueue<E> exte
         // enough padding for 64bytes with 4byte refs
         Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe;
         PaddedAtomicReference(T r) { super(r); }
+        private static final long serialVersionUID = 8170090609809740854L;
     }
 
 
     /** head of the queue */
-    private transient final PaddedAtomicReference<QNode> head;
+    private transient final PaddedAtomicReference<Node<E>> head;
+
     /** tail of the queue */
-    private transient final PaddedAtomicReference<QNode> tail;
+    private transient final PaddedAtomicReference<Node<E>> tail;
 
     /**
      * Reference to a cancelled node that might not yet have been
      * unlinked from queue because it was the last inserted node
      * when it cancelled.
      */
-    private transient final PaddedAtomicReference<QNode> cleanMe;
+    private transient final PaddedAtomicReference<Node<E>> cleanMe;
 
     /**
      * Tries to cas nh as new head; if successful, unlink
      * old head's next node to avoid garbage retention.
      */
-    private boolean advanceHead(QNode h, QNode nh) {
+    private boolean advanceHead(Node<E> h, Node<E> nh) {
         if (h == head.get() && head.compareAndSet(h, nh)) {
-            h.next = h; // forget old next
+            h.clearNext(); // forget old next
             return true;
         }
         return false;
@@ -161,25 +168,26 @@ public class LinkedTransferQueue<E> exte
      * Puts or takes an item. Used for most queue operations (except
      * poll() and tryTransfer()). See the similar code in
      * SynchronousQueue for detailed explanation.
+     *
      * @param e the item or if null, signifies that this is a take
      * @param mode the wait mode: NOWAIT, TIMEOUT, WAIT
      * @param nanos timeout in nanosecs, used only if mode is TIMEOUT
      * @return an item, or null on failure
      */
-    private Object xfer(Object e, int mode, long nanos) {
+    private E xfer(E e, int mode, long nanos) {
         boolean isData = (e != null);
-        QNode s = null;
-        final PaddedAtomicReference<QNode> head = this.head;
-        final PaddedAtomicReference<QNode> tail = this.tail;
+        Node<E> s = null;
+        final PaddedAtomicReference<Node<E>> head = this.head;
+        final PaddedAtomicReference<Node<E>> tail = this.tail;
 
         for (;;) {
-            QNode t = tail.get();
-            QNode h = head.get();
+            Node<E> t = tail.get();
+            Node<E> h = head.get();
 
             if (t != null && (t == h || t.isData == isData)) {
                 if (s == null)
-                    s = new QNode(e, isData);
-                QNode last = t.next;
+                    s = new Node<E>(e, isData);
+                Node<E> last = t.next;
                 if (last != null) {
                     if (t == tail.get())
                         tail.compareAndSet(t, last);
@@ -191,13 +199,13 @@ public class LinkedTransferQueue<E> exte
             }
 
             else if (h != null) {
-                QNode first = h.next;
+                Node<E> first = h.next;
                 if (t == tail.get() && first != null &&
                     advanceHead(h, first)) {
                     Object x = first.get();
                     if (x != first && first.compareAndSet(x, e)) {
                         LockSupport.unpark(first.waiter);
-                        return isData? e : x;
+                        return isData ? e : (E) x;
                     }
                 }
             }
@@ -207,19 +215,19 @@ public class LinkedTransferQueue<E> exte
 
     /**
      * Version of xfer for poll() and tryTransfer, which
-     * simplifies control paths both here and in xfer
+     * simplifies control paths both here and in xfer.
      */
-    private Object fulfill(Object e) {
+    private E fulfill(E e) {
         boolean isData = (e != null);
-        final PaddedAtomicReference<QNode> head = this.head;
-        final PaddedAtomicReference<QNode> tail = this.tail;
+        final PaddedAtomicReference<Node<E>> head = this.head;
+        final PaddedAtomicReference<Node<E>> tail = this.tail;
 
         for (;;) {
-            QNode t = tail.get();
-            QNode h = head.get();
+            Node<E> t = tail.get();
+            Node<E> h = head.get();
 
             if (t != null && (t == h || t.isData == isData)) {
-                QNode last = t.next;
+                Node<E> last = t.next;
                 if (t == tail.get()) {
                     if (last != null)
                         tail.compareAndSet(t, last);
@@ -228,14 +236,14 @@ public class LinkedTransferQueue<E> exte
                 }
             }
             else if (h != null) {
-                QNode first = h.next;
+                Node<E> first = h.next;
                 if (t == tail.get() &&
                     first != null &&
                     advanceHead(h, first)) {
                     Object x = first.get();
                     if (x != first && first.compareAndSet(x, e)) {
                         LockSupport.unpark(first.waiter);
-                        return isData? e : x;
+                        return isData ? e : (E) x;
                     }
                 }
             }
@@ -253,12 +261,12 @@ public class LinkedTransferQueue<E> exte
      * @param nanos timeout value
      * @return matched item, or s if cancelled
      */
-    private Object awaitFulfill(QNode pred, QNode s, Object e,
-                                int mode, long nanos) {
+    private E awaitFulfill(Node<E> pred, Node<E> s, E e,
+                           int mode, long nanos) {
         if (mode == NOWAIT)
             return null;
 
-        long lastTime = (mode == TIMEOUT)? System.nanoTime() : 0;
+        long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0;
         Thread w = Thread.currentThread();
         int spins = -1; // set to desired spin count below
         for (;;) {
@@ -267,13 +275,13 @@ public class LinkedTransferQueue<E> exte
             Object x = s.get();
             if (x != e) {                 // Node was matched or cancelled
                 advanceHead(pred, s);     // unlink if head
-                if (x == s) {              // was cancelled
+                if (x == s) {             // was cancelled
                     clean(pred, s);
                     return null;
                 }
                 else if (x != null) {
                     s.set(s);             // avoid garbage retention
-                    return x;
+                    return (E) x;
                 }
                 else
                     return e;
@@ -288,9 +296,9 @@ public class LinkedTransferQueue<E> exte
                 }
             }
             if (spins < 0) {
-                QNode h = head.get(); // only spin if at head
+                Node<E> h = head.get(); // only spin if at head
                 spins = ((h != null && h.next == s) ?
-                         (mode == TIMEOUT?
+                         ((mode == TIMEOUT) ?
                           maxTimedSpins : maxUntimedSpins) : 0);
             }
             if (spins > 0)
@@ -298,14 +306,12 @@ public class LinkedTransferQueue<E> exte
             else if (s.waiter == null)
                 s.waiter = w;
             else if (mode != TIMEOUT) {
-                //                LockSupport.park(this);
-                LockSupport.park(); // allows run on java5
+                LockSupport.park(this);
                 s.waiter = null;
                 spins = -1;
             }
             else if (nanos > spinForTimeoutThreshold) {
-                //                LockSupport.parkNanos(this, nanos);
-                LockSupport.parkNanos(nanos);
+                LockSupport.parkNanos(this, nanos);
                 s.waiter = null;
                 spins = -1;
             }
@@ -313,18 +319,18 @@ public class LinkedTransferQueue<E> exte
     }
 
     /**
-     * Returns validated tail for use in cleaning methods
+     * Returns validated tail for use in cleaning methods.
      */
-    private QNode getValidatedTail() {
+    private Node<E> getValidatedTail() {
         for (;;) {
-            QNode h = head.get();
-            QNode first = h.next;
+            Node<E> h = head.get();
+            Node<E> first = h.next;
             if (first != null && first.next == first) { // help advance
                 advanceHead(h, first);
                 continue;
             }
-            QNode t = tail.get();
-            QNode last = t.next;
+            Node<E> t = tail.get();
+            Node<E> last = t.next;
             if (t == tail.get()) {
                 if (last != null)
                     tail.compareAndSet(t, last); // help advance
@@ -332,20 +338,25 @@ public class LinkedTransferQueue<E> exte
                     return t;
             }
         }
-    }    
+    }
 
     /**
      * Gets rid of cancelled node s with original predecessor pred.
+     *
      * @param pred predecessor of cancelled node
      * @param s the cancelled node
      */
-    private void clean(QNode pred, QNode s) {
+    private void clean(Node<E> pred, Node<E> s) {
         Thread w = s.waiter;
         if (w != null) {             // Wake up thread
             s.waiter = null;
             if (w != Thread.currentThread())
                 LockSupport.unpark(w);
         }
+
+        if (pred == null)
+            return;
+
         /*
          * At any given time, exactly one node on list cannot be
          * deleted -- the last inserted node. To accommodate this, if
@@ -355,11 +366,11 @@ public class LinkedTransferQueue<E> exte
          * processed, so this always terminates.
          */
         while (pred.next == s) {
-            QNode oldpred = reclean();  // First, help get rid of cleanMe
-            QNode t = getValidatedTail();
+            Node<E> oldpred = reclean();  // First, help get rid of cleanMe
+            Node<E> t = getValidatedTail();
             if (s != t) {               // If not tail, try to unsplice
-                QNode sn = s.next;      // s.next == s means s already off list
-                if (sn == s || pred.casNext(s, sn)) 
+                Node<E> sn = s.next;      // s.next == s means s already off list
+                if (sn == s || pred.casNext(s, sn))
                     break;
             }
             else if (oldpred == pred || // Already saved
@@ -371,10 +382,11 @@ public class LinkedTransferQueue<E> exte
     /**
      * Tries to unsplice the cancelled node held in cleanMe that was
      * previously uncleanable because it was at tail.
+     *
      * @return current cleanMe node (or null)
      */
-    private QNode reclean() {
-        /* 
+    private Node<E> reclean() {
+        /*
          * cleanMe is, or at one time was, predecessor of cancelled
          * node s that was the tail so could not be unspliced.  If s
          * is no longer the tail, try to unsplice if necessary and
@@ -383,14 +395,14 @@ public class LinkedTransferQueue<E> exte
          * points to a cancelled node that must be unspliced -- if
          * not, we can (must) clear cleanMe without unsplicing.
          * This can loop only due to contention on casNext or
-         * clearing cleanMe. 
+         * clearing cleanMe.
          */
-        QNode pred;
+        Node<E> pred;
         while ((pred = cleanMe.get()) != null) {
-            QNode t = getValidatedTail();
-            QNode s = pred.next;
-            if (s != t) { 
-                QNode sn;
+            Node<E> t = getValidatedTail();
+            Node<E> s = pred.next;
+            if (s != t) {
+                Node<E> sn;
                 if (s == null || s == pred || s.get() != s ||
                     (sn = s.next) == s || pred.casNext(s, sn))
                     cleanMe.compareAndSet(pred, null);
@@ -402,19 +414,20 @@ public class LinkedTransferQueue<E> exte
     }
 
     /**
-     * Creates an initially empty <tt>LinkedTransferQueue</tt>.
+     * Creates an initially empty {@code LinkedTransferQueue}.
      */
     public LinkedTransferQueue() {
-        QNode dummy = new QNode(null, false);
-        head = new PaddedAtomicReference<QNode>(dummy);
-        tail = new PaddedAtomicReference<QNode>(dummy);
-        cleanMe = new PaddedAtomicReference<QNode>(null);
+        Node<E> dummy = new Node<E>(null, false);
+        head = new PaddedAtomicReference<Node<E>>(dummy);
+        tail = new PaddedAtomicReference<Node<E>>(dummy);
+        cleanMe = new PaddedAtomicReference<Node<E>>(null);
     }
 
     /**
-     * Creates a <tt>LinkedTransferQueue</tt>
+     * Creates a {@code LinkedTransferQueue}
      * initially containing the elements of the given collection,
      * added in traversal order of the collection's iterator.
+     *
      * @param c the collection of elements to initially contain
      * @throws NullPointerException if the specified collection or any
      *         of its elements are null
@@ -444,6 +457,12 @@ public class LinkedTransferQueue<E> exte
         return true;
     }
 
+    public boolean add(E e) {
+        if (e == null) throw new NullPointerException();
+        xfer(e, NOWAIT, 0);
+        return true;
+    }
+
     public void transfer(E e) throws InterruptedException {
         if (e == null) throw new NullPointerException();
         if (xfer(e, WAIT, 0) == null) {
@@ -470,7 +489,7 @@ public class LinkedTransferQueue<E> exte
     public E take() throws InterruptedException {
         Object e = xfer(null, WAIT, 0);
         if (e != null)
-            return (E)e;
+            return (E) e;
         Thread.interrupted();
         throw new InterruptedException();
     }
@@ -478,12 +497,12 @@ public class LinkedTransferQueue<E> exte
     public E poll(long timeout, TimeUnit unit) throws InterruptedException {
         Object e = xfer(null, TIMEOUT, unit.toNanos(timeout));
         if (e != null || !Thread.interrupted())
-            return (E)e;
+            return (E) e;
         throw new InterruptedException();
     }
 
     public E poll() {
-        return (E)fulfill(null);
+        return fulfill(null);
     }
 
     public int drainTo(Collection<? super E> c) {
@@ -517,15 +536,15 @@ public class LinkedTransferQueue<E> exte
     // Traversal-based methods
 
     /**
-     * Return head after performing any outstanding helping steps
+     * Returns head after performing any outstanding helping steps.
      */
-    private QNode traversalHead() {
+    private Node<E> traversalHead() {
         for (;;) {
-            QNode t = tail.get();
-            QNode h = head.get();
+            Node<E> t = tail.get();
+            Node<E> h = head.get();
             if (h != null && t != null) {
-                QNode last = t.next;
-                QNode first = h.next;
+                Node<E> last = t.next;
+                Node<E> first = h.next;
                 if (t == tail.get()) {
                     if (last != null)
                         tail.compareAndSet(t, last);
@@ -540,6 +559,7 @@ public class LinkedTransferQueue<E> exte
                         return h;
                 }
             }
+            reclean();
         }
     }
 
@@ -556,63 +576,75 @@ public class LinkedTransferQueue<E> exte
      * if subsequently removed.
      */
     class Itr implements Iterator<E> {
-        QNode nextNode;    // Next node to return next
-        QNode currentNode; // last returned node, for remove()
-        QNode prevNode;    // predecessor of last returned node
-        E nextItem;        // Cache of next item, once commited to in next
+        Node<E> next;        // node to return next
+        Node<E> pnext;       // predecessor of next
+        Node<E> snext;       // successor of next
+        Node<E> curr;        // last returned node, for remove()
+        Node<E> pcurr;       // predecessor of curr, for remove()
+        E nextItem;        // Cache of next item, once committed to in next
 
         Itr() {
-            nextNode = traversalHead();
-            advance();
+            findNext();
         }
 
-        E advance() {
-            prevNode = currentNode;
-            currentNode = nextNode;
-            E x = nextItem;
-
-            QNode p = nextNode.next;
+        /**
+         * Ensures next points to next valid node, or null if none.
+         */
+        void findNext() {
             for (;;) {
-                if (p == null || !p.isData) {
-                    nextNode = null;
-                    nextItem = null;
-                    return x;
-                }
-                Object item = p.get();
-                if (item != p && item != null) {
-                    nextNode = p;
-                    nextItem = (E)item;
-                    return x;
+                Node<E> pred = pnext;
+                Node<E> q = next;
+                if (pred == null || pred == q) {
+                    pred = traversalHead();
+                    q = pred.next;
+                }
+                if (q == null || !q.isData) {
+                    next = null;
+                    return;
+                }
+                Object x = q.get();
+                Node<E> s = q.next;
+                if (x != null && q != x && q != s) {
+                    nextItem = (E) x;
+                    snext = s;
+                    pnext = pred;
+                    next = q;
+                    return;
                 }
-                prevNode = p;
-                p = p.next;
+                pnext = q;
+                next = s;
             }
         }
 
         public boolean hasNext() {
-            return nextNode != null;
+            return next != null;
         }
 
         public E next() {
-            if (nextNode == null) throw new NoSuchElementException();
-            return advance();
+            if (next == null) throw new NoSuchElementException();
+            pcurr = pnext;
+            curr = next;
+            pnext = next;
+            next = snext;
+            E x = nextItem;
+            findNext();
+            return x;
         }
 
         public void remove() {
-            QNode p = currentNode;
-            QNode prev = prevNode;
-            if (prev == null || p == null)
+            Node<E> p = curr;
+            if (p == null)
                 throw new IllegalStateException();
             Object x = p.get();
             if (x != null && x != p && p.compareAndSet(x, p))
-                clean(prev, p);
+                clean(pcurr, p);
         }
     }
 
     public E peek() {
         for (;;) {
-            QNode h = traversalHead();
-            QNode p = h.next;
+            Node<E> h = traversalHead();
+            Node<E> p = h.next;
             if (p == null)
                 return null;
             Object x = p.get();
@@ -620,15 +652,15 @@ public class LinkedTransferQueue<E> exte
                 if (!p.isData)
                     return null;
                 if (x != null)
-                    return (E)x;
+                    return (E) x;
             }
         }
     }
 
     public boolean isEmpty() {
         for (;;) {
-            QNode h = traversalHead();
-            QNode p = h.next;
+            Node<E> h = traversalHead();
+            Node<E> p = h.next;
             if (p == null)
                 return true;
             Object x = p.get();
@@ -643,8 +675,8 @@ public class LinkedTransferQueue<E> exte
 
     public boolean hasWaitingConsumer() {
         for (;;) {
-            QNode h = traversalHead();
-            QNode p = h.next;
+            Node<E> h = traversalHead();
+            Node<E> p = h.next;
             if (p == null)
                 return false;
             Object x = p.get();
@@ -655,8 +687,8 @@ public class LinkedTransferQueue<E> exte
 
     /**
      * Returns the number of elements in this queue.  If this queue
-     * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
-     * <tt>Integer.MAX_VALUE</tt>.
+     * contains more than {@code Integer.MAX_VALUE} elements, returns
+     * {@code Integer.MAX_VALUE}.
      *
      * <p>Beware that, unlike in most collections, this method is
      * <em>NOT</em> a constant-time operation. Because of the
@@ -667,8 +699,8 @@ public class LinkedTransferQueue<E> exte
      */
     public int size() {
         int count = 0;
-        QNode h = traversalHead();
-        for (QNode p = h.next; p != null && p.isData; p = p.next) {
+        Node<E> h = traversalHead();
+        for (Node<E> p = h.next; p != null && p.isData; p = p.next) {
             Object x = p.get();
             if (x != null && x != p) {
                 if (++count == Integer.MAX_VALUE) // saturated
@@ -680,8 +712,8 @@ public class LinkedTransferQueue<E> exte
 
     public int getWaitingConsumerCount() {
         int count = 0;
-        QNode h = traversalHead();
-        for (QNode p = h.next; p != null && !p.isData; p = p.next) {
+        Node<E> h = traversalHead();
+        for (Node<E> p = h.next; p != null && !p.isData; p = p.next) {
             if (p.get() == null) {
                 if (++count == Integer.MAX_VALUE)
                     break;
@@ -694,18 +726,40 @@ public class LinkedTransferQueue<E> exte
         return Integer.MAX_VALUE;
     }
 
+    public boolean remove(Object o) {
+        if (o == null)
+            return false;
+        for (;;) {
+            Node<E> pred = traversalHead();
+            for (;;) {
+                Node<E> q = pred.next;
+                if (q == null || !q.isData)
+                    return false;
+                if (q == pred) // restart
+                    break;
+                Object x = q.get();
+                if (x != null && x != q && o.equals(x) &&
+                    q.compareAndSet(x, q)) {
+                    clean(pred, q);
+                    return true;
+                }
+                pred = q;
+            }
+        }
+    }
+
     /**
      * Save the state to a stream (that is, serialize it).
      *
-     * @serialData All of the elements (each an <tt>E</tt>) in
+     * @serialData All of the elements (each an {@code E}) in
      * the proper order, followed by a null
      * @param s the stream
      */
     private void writeObject(java.io.ObjectOutputStream s)
         throws java.io.IOException {
         s.defaultWriteObject();
-        for (Iterator<E> it = iterator(); it.hasNext(); )
-            s.writeObject(it.next());
+        for (E e : this)
+            s.writeObject(e);
         // Use trailing null as sentinel
         s.writeObject(null);
     }
@@ -713,6 +767,7 @@ public class LinkedTransferQueue<E> exte
     /**
      * Reconstitute the Queue instance from a stream (that is,
      * deserialize it).
+     *
      * @param s the stream
      */
     private void readObject(java.io.ObjectInputStream s)
@@ -720,7 +775,7 @@ public class LinkedTransferQueue<E> exte
         s.defaultReadObject();
         resetHeadAndTail();
         for (;;) {
-            E item = (E)s.readObject();
+            @SuppressWarnings("unchecked") E item = (E) s.readObject();
             if (item == null)
                 break;
             else
@@ -728,43 +783,60 @@ public class LinkedTransferQueue<E> exte
         }
     }
 
-
     // Support for resetting head/tail while deserializing
+    private void resetHeadAndTail() {
+        Node<E> dummy = new Node<E>(null, false);
+        UNSAFE.putObjectVolatile(this, headOffset,
+                                 new PaddedAtomicReference<Node<E>>(dummy));
+        UNSAFE.putObjectVolatile(this, tailOffset,
+                                 new PaddedAtomicReference<Node<E>>(dummy));
+        UNSAFE.putObjectVolatile(this, cleanMeOffset,
+                                 new PaddedAtomicReference<Node<E>>(null));
+    }
 
-    // Temporary Unsafe mechanics for preliminary release
-    private static final Unsafe _unsafe;
-    private static final long headOffset;
-    private static final long tailOffset;
-    private static final long cleanMeOffset;
-    static {
+    // Unsafe mechanics for jsr166y 3rd party package.
+    private static sun.misc.Unsafe getUnsafe() {
         try {
-            if (LinkedTransferQueue.class.getClassLoader() != null) {
-                Field f = Unsafe.class.getDeclaredField("theUnsafe");
-                f.setAccessible(true);
-                _unsafe = (Unsafe)f.get(null);
+            return sun.misc.Unsafe.getUnsafe();
+        } catch (SecurityException se) {
+            try {
+                return java.security.AccessController.doPrivileged
+                    (new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
+                        public sun.misc.Unsafe run() throws Exception {
+                            return getUnsafeByReflection();
+                        }});
+            } catch (java.security.PrivilegedActionException e) {
+                throw new RuntimeException("Could not initialize intrinsics",
+                                           e.getCause());
             }
-            else
-                _unsafe = Unsafe.getUnsafe();
-            headOffset = _unsafe.objectFieldOffset
-                (LinkedTransferQueue.class.getDeclaredField("head"));
-            tailOffset = _unsafe.objectFieldOffset
-                (LinkedTransferQueue.class.getDeclaredField("tail"));
-            cleanMeOffset = _unsafe.objectFieldOffset
-                (LinkedTransferQueue.class.getDeclaredField("cleanMe"));
-        } catch (Exception e) {
-            throw new RuntimeException("Could not initialize intrinsics", e);
         }
     }
 
-    private void resetHeadAndTail() {
-        QNode dummy = new QNode(null, false);
-        _unsafe.putObjectVolatile(this, headOffset, 
-                                  new PaddedAtomicReference<QNode>(dummy));
-        _unsafe.putObjectVolatile(this, tailOffset, 
-                                  new PaddedAtomicReference<QNode>(dummy));
-        _unsafe.putObjectVolatile(this, cleanMeOffset,
-                                  new PaddedAtomicReference<QNode>(null));
+    private static sun.misc.Unsafe getUnsafeByReflection()
+            throws NoSuchFieldException, IllegalAccessException {
+        java.lang.reflect.Field f =
+            sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
+        f.setAccessible(true);
+        return (sun.misc.Unsafe) f.get(null);
+    }
 
+    private static long fieldOffset(String fieldName, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to Error
+            NoSuchFieldError error = new NoSuchFieldError(fieldName);
+            error.initCause(e);
+            throw error;
+        }
     }
 
+    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+    static final long headOffset =
+        fieldOffset("head", LinkedTransferQueue.class);
+    static final long tailOffset =
+        fieldOffset("tail", LinkedTransferQueue.class);
+    static final long cleanMeOffset =
+        fieldOffset("cleanMe", LinkedTransferQueue.class);
+
 }