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From hinde...@apache.org
Subject svn commit: r800934 [5/6] - in /harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent: ./ locks/
Date Tue, 04 Aug 2009 19:39:25 GMT
Added: harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java?rev=800934&view=auto
==============================================================================
--- harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java (added)
+++ harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java Tue Aug  4 19:39:24 2009
@@ -0,0 +1,2072 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent.locks;
+import java.util.*;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.*;
+import sun.misc.Unsafe;
+
+/**
+ * A version of {@link AbstractQueuedSynchronizer} in
+ * which synchronization state is maintained as a <tt>long</tt>.
+ * This class has exactly the same structure, properties, and methods
+ * as <tt>AbstractQueuedSynchronizer</tt> with the exception
+ * that all state-related parameters and results are defined
+ * as <tt>long</tt> rather than <tt>int</tt>. This class
+ * may be useful when creating synchronizers such as
+ * multilevel locks and barriers that require
+ * 64 bits of state.
+ *
+ * <p>See {@link AbstractQueuedSynchronizer} for usage
+ * notes and examples.
+ *
+ * @since 1.6
+ * @author Doug Lea
+ */
+public abstract class AbstractQueuedLongSynchronizer
+    extends AbstractOwnableSynchronizer
+    implements java.io.Serializable {
+
+    private static final long serialVersionUID = 7373984972572414692L;
+
+    /*
+      To keep sources in sync, the remainder of this source file is
+      exactly cloned from AbstractQueuedSynchronizer, replacing class
+      name and changing ints related with sync state to longs. Please
+      keep it that way.
+    */
+
+    /**
+     * Creates a new <tt>AbstractQueuedLongSynchronizer</tt> instance
+     * with initial synchronization state of zero.
+     */
+    protected AbstractQueuedLongSynchronizer() { }
+
+    /**
+     * Wait queue node class.
+     *
+     * <p>The wait queue is a variant of a "CLH" (Craig, Landin, and
+     * Hagersten) lock queue. CLH locks are normally used for
+     * spinlocks.  We instead use them for blocking synchronizers, but
+     * use the same basic tactic of holding some of the control
+     * information about a thread in the predecessor of its node.  A
+     * "status" field in each node keeps track of whether a thread
+     * should block.  A node is signalled when its predecessor
+     * releases.  Each node of the queue otherwise serves as a
+     * specific-notification-style monitor holding a single waiting
+     * thread. The status field does NOT control whether threads are
+     * granted locks etc though.  A thread may try to acquire if it is
+     * first in the queue. But being first does not guarantee success;
+     * it only gives the right to contend.  So the currently released
+     * contender thread may need to rewait.
+     *
+     * <p>To enqueue into a CLH lock, you atomically splice it in as new
+     * tail. To dequeue, you just set the head field.
+     * <pre>
+     *      +------+  prev +-----+       +-----+
+     * head |      | <---- |     | <---- |     |  tail
+     *      +------+       +-----+       +-----+
+     * </pre>
+     *
+     * <p>Insertion into a CLH queue requires only a single atomic
+     * operation on "tail", so there is a simple atomic point of
+     * demarcation from unqueued to queued. Similarly, dequeing
+     * involves only updating the "head". However, it takes a bit
+     * more work for nodes to determine who their successors are,
+     * in part to deal with possible cancellation due to timeouts
+     * and interrupts.
+     *
+     * <p>The "prev" links (not used in original CLH locks), are mainly
+     * needed to handle cancellation. If a node is cancelled, its
+     * successor is (normally) relinked to a non-cancelled
+     * predecessor. For explanation of similar mechanics in the case
+     * of spin locks, see the papers by Scott and Scherer at
+     * http://www.cs.rochester.edu/u/scott/synchronization/
+     *
+     * <p>We also use "next" links to implement blocking mechanics.
+     * The thread id for each node is kept in its own node, so a
+     * predecessor signals the next node to wake up by traversing
+     * next link to determine which thread it is.  Determination of
+     * successor must avoid races with newly queued nodes to set
+     * the "next" fields of their predecessors.  This is solved
+     * when necessary by checking backwards from the atomically
+     * updated "tail" when a node's successor appears to be null.
+     * (Or, said differently, the next-links are an optimization
+     * so that we don't usually need a backward scan.)
+     *
+     * <p>Cancellation introduces some conservatism to the basic
+     * algorithms.  Since we must poll for cancellation of other
+     * nodes, we can miss noticing whether a cancelled node is
+     * ahead or behind us. This is dealt with by always unparking
+     * successors upon cancellation, allowing them to stabilize on
+     * a new predecessor, unless we can identify an uncancelled
+     * predecessor who will carry this responsibility.
+     *
+     * <p>CLH queues need a dummy header node to get started. But
+     * we don't create them on construction, because it would be wasted
+     * effort if there is never contention. Instead, the node
+     * is constructed and head and tail pointers are set upon first
+     * contention.
+     *
+     * <p>Threads waiting on Conditions use the same nodes, but
+     * use an additional link. Conditions only need to link nodes
+     * in simple (non-concurrent) linked queues because they are
+     * only accessed when exclusively held.  Upon await, a node is
+     * inserted into a condition queue.  Upon signal, the node is
+     * transferred to the main queue.  A special value of status
+     * field is used to mark which queue a node is on.
+     *
+     * <p>Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill
+     * Scherer and Michael Scott, along with members of JSR-166
+     * expert group, for helpful ideas, discussions, and critiques
+     * on the design of this class.
+     */
+    static final class Node {
+        /** Marker to indicate a node is waiting in shared mode */
+        static final Node SHARED = new Node();
+        /** Marker to indicate a node is waiting in exclusive mode */
+        static final Node EXCLUSIVE = null;
+
+        /** waitStatus value to indicate thread has cancelled */
+        static final int CANCELLED =  1;
+        /** waitStatus value to indicate successor's thread needs unparking */
+        static final int SIGNAL    = -1;
+        /** waitStatus value to indicate thread is waiting on condition */
+        static final int CONDITION = -2;
+        /**
+         * waitStatus value to indicate the next acquireShared should
+         * unconditionally propagate
+         */
+        static final int PROPAGATE = -3;
+
+        /**
+         * Status field, taking on only the values:
+         *   SIGNAL:     The successor of this node is (or will soon be)
+         *               blocked (via park), so the current node must
+         *               unpark its successor when it releases or
+         *               cancels. To avoid races, acquire methods must
+         *               first indicate they need a signal,
+         *               then retry the atomic acquire, and then,
+         *               on failure, block.
+         *   CANCELLED:  This node is cancelled due to timeout or interrupt.
+         *               Nodes never leave this state. In particular,
+         *               a thread with cancelled node never again blocks.
+         *   CONDITION:  This node is currently on a condition queue.
+         *               It will not be used as a sync queue node
+         *               until transferred, at which time the status
+         *               will be set to 0. (Use of this value here has
+         *               nothing to do with the other uses of the
+         *               field, but simplifies mechanics.)
+         *   PROPAGATE:  A releaseShared should be propagated to other
+         *               nodes. This is set (for head node only) in
+         *               doReleaseShared to ensure propagation
+         *               continues, even if other operations have
+         *               since intervened.
+         *   0:          None of the above
+         *
+         * The values are arranged numerically to simplify use.
+         * Non-negative values mean that a node doesn't need to
+         * signal. So, most code doesn't need to check for particular
+         * values, just for sign.
+         *
+         * The field is initialized to 0 for normal sync nodes, and
+         * CONDITION for condition nodes.  It is modified using CAS
+         * (or when possible, unconditional volatile writes).
+         */
+        volatile int waitStatus;
+
+        /**
+         * Link to predecessor node that current node/thread relies on
+         * for checking waitStatus. Assigned during enqueing, and nulled
+         * out (for sake of GC) only upon dequeuing.  Also, upon
+         * cancellation of a predecessor, we short-circuit while
+         * finding a non-cancelled one, which will always exist
+         * because the head node is never cancelled: A node becomes
+         * head only as a result of successful acquire. A
+         * cancelled thread never succeeds in acquiring, and a thread only
+         * cancels itself, not any other node.
+         */
+        volatile Node prev;
+
+        /**
+         * Link to the successor node that the current node/thread
+         * unparks upon release. Assigned during enqueuing, adjusted
+         * when bypassing cancelled predecessors, and nulled out (for
+         * sake of GC) when dequeued.  The enq operation does not
+         * assign next field of a predecessor until after attachment,
+         * so seeing a null next field does not necessarily mean that
+         * node is at end of queue. However, if a next field appears
+         * to be null, we can scan prev's from the tail to
+         * double-check.  The next field of cancelled nodes is set to
+         * point to the node itself instead of null, to make life
+         * easier for isOnSyncQueue.
+         */
+        volatile Node next;
+
+        /**
+         * The thread that enqueued this node.  Initialized on
+         * construction and nulled out after use.
+         */
+        volatile Thread thread;
+
+        /**
+         * Link to next node waiting on condition, or the special
+         * value SHARED.  Because condition queues are accessed only
+         * when holding in exclusive mode, we just need a simple
+         * linked queue to hold nodes while they are waiting on
+         * conditions. They are then transferred to the queue to
+         * re-acquire. And because conditions can only be exclusive,
+         * we save a field by using special value to indicate shared
+         * mode.
+         */
+        Node nextWaiter;
+
+        /**
+         * Returns true if node is waiting in shared mode
+         */
+        final boolean isShared() {
+            return nextWaiter == SHARED;
+        }
+
+        /**
+         * Returns previous node, or throws NullPointerException if null.
+         * Use when predecessor cannot be null.  The null check could
+         * be elided, but is present to help the VM.
+         *
+         * @return the predecessor of this node
+         */
+        final Node predecessor() throws NullPointerException {
+            Node p = prev;
+            if (p == null)
+                throw new NullPointerException();
+            else
+                return p;
+        }
+
+        Node() {    // Used to establish initial head or SHARED marker
+        }
+
+        Node(Thread thread, Node mode) {     // Used by addWaiter
+            this.nextWaiter = mode;
+            this.thread = thread;
+        }
+
+        Node(Thread thread, int waitStatus) { // Used by Condition
+            this.waitStatus = waitStatus;
+            this.thread = thread;
+        }
+    }
+
+    /**
+     * Head of the wait queue, lazily initialized.  Except for
+     * initialization, it is modified only via method setHead.  Note:
+     * If head exists, its waitStatus is guaranteed not to be
+     * CANCELLED.
+     */
+    private transient volatile Node head;
+
+    /**
+     * Tail of the wait queue, lazily initialized.  Modified only via
+     * method enq to add new wait node.
+     */
+    private transient volatile Node tail;
+
+    /**
+     * The synchronization state.
+     */
+    private volatile long state;
+
+    /**
+     * Returns the current value of synchronization state.
+     * This operation has memory semantics of a <tt>volatile</tt> read.
+     * @return current state value
+     */
+    protected final long getState() {
+        return state;
+    }
+
+    /**
+     * Sets the value of synchronization state.
+     * This operation has memory semantics of a <tt>volatile</tt> write.
+     * @param newState the new state value
+     */
+    protected final void setState(long newState) {
+        state = newState;
+    }
+
+    /**
+     * Atomically sets synchronization state to the given updated
+     * value if the current state value equals the expected value.
+     * This operation has memory semantics of a <tt>volatile</tt> read
+     * and write.
+     *
+     * @param expect the expected value
+     * @param update the new value
+     * @return true if successful. False return indicates that the actual
+     *         value was not equal to the expected value.
+     */
+    protected final boolean compareAndSetState(long expect, long update) {
+        // See below for intrinsics setup to support this
+        return unsafe.compareAndSwapLong(this, stateOffset, expect, update);
+    }
+
+    // Queuing utilities
+
+    /**
+     * The number of nanoseconds for which it is faster to spin
+     * rather than to use timed park. A rough estimate suffices
+     * to improve responsiveness with very short timeouts.
+     */
+    static final long spinForTimeoutThreshold = 1000L;
+
+    /**
+     * Inserts node into queue, initializing if necessary. See picture above.
+     * @param node the node to insert
+     * @return node's predecessor
+     */
+    private Node enq(final Node node) {
+        for (;;) {
+            Node t = tail;
+            if (t == null) { // Must initialize
+                if (compareAndSetHead(new Node()))
+                    tail = head;
+            } else {
+                node.prev = t;
+                if (compareAndSetTail(t, node)) {
+                    t.next = node;
+                    return t;
+                }
+            }
+        }
+    }
+
+    /**
+     * Creates and enqueues node for current thread and given mode.
+     *
+     * @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared
+     * @return the new node
+     */
+    private Node addWaiter(Node mode) {
+        Node node = new Node(Thread.currentThread(), mode);
+        // Try the fast path of enq; backup to full enq on failure
+        Node pred = tail;
+        if (pred != null) {
+            node.prev = pred;
+            if (compareAndSetTail(pred, node)) {
+                pred.next = node;
+                return node;
+            }
+        }
+        enq(node);
+        return node;
+    }
+
+    /**
+     * Sets head of queue to be node, thus dequeuing. Called only by
+     * acquire methods.  Also nulls out unused fields for sake of GC
+     * and to suppress unnecessary signals and traversals.
+     *
+     * @param node the node
+     */
+    private void setHead(Node node) {
+        head = node;
+        node.thread = null;
+        node.prev = null;
+    }
+
+    /**
+     * Wakes up node's successor, if one exists.
+     *
+     * @param node the node
+     */
+    private void unparkSuccessor(Node node) {
+        /*
+         * If status is negative (i.e., possibly needing signal) try
+         * to clear in anticipation of signalling.  It is OK if this
+         * fails or if status is changed by waiting thread.
+         */
+        int ws = node.waitStatus;
+        if (ws < 0)
+            compareAndSetWaitStatus(node, ws, 0);
+
+        /*
+         * Thread to unpark is held in successor, which is normally
+         * just the next node.  But if cancelled or apparently null,
+         * traverse backwards from tail to find the actual
+         * non-cancelled successor.
+         */
+        Node s = node.next;
+        if (s == null || s.waitStatus > 0) {
+            s = null;
+            for (Node t = tail; t != null && t != node; t = t.prev)
+                if (t.waitStatus <= 0)
+                    s = t;
+        }
+        if (s != null)
+            LockSupport.unpark(s.thread);
+    }
+
+    /**
+     * Release action for shared mode -- signal successor and ensure
+     * propagation. (Note: For exclusive mode, release just amounts
+     * to calling unparkSuccessor of head if it needs signal.)
+     */
+    private void doReleaseShared() {
+        /*
+         * Ensure that a release propagates, even if there are other
+         * in-progress acquires/releases.  This proceeds in the usual
+         * way of trying to unparkSuccessor of head if it needs
+         * signal. But if it does not, status is set to PROPAGATE to
+         * ensure that upon release, propagation continues.
+         * Additionally, we must loop in case a new node is added
+         * while we are doing this. Also, unlike other uses of
+         * unparkSuccessor, we need to know if CAS to reset status
+         * fails, if so rechecking.
+         */
+        for (;;) {
+            Node h = head;
+            if (h != null && h != tail) {
+                int ws = h.waitStatus;
+                if (ws == Node.SIGNAL) {
+                    if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))
+                        continue;            // loop to recheck cases
+                    unparkSuccessor(h);
+                }
+                else if (ws == 0 &&
+                         !compareAndSetWaitStatus(h, 0, Node.PROPAGATE))
+                    continue;                // loop on failed CAS
+            }
+            if (h == head)                   // loop if head changed
+                break;
+        }
+    }
+
+    /**
+     * Sets head of queue, and checks if successor may be waiting
+     * in shared mode, if so propagating if either propagate > 0 or
+     * PROPAGATE status was set.
+     *
+     * @param node the node
+     * @param propagate the return value from a tryAcquireShared
+     */
+    private void setHeadAndPropagate(Node node, long propagate) {
+        Node h = head; // Record old head for check below
+        setHead(node);
+        /*
+         * Try to signal next queued node if:
+         *   Propagation was indicated by caller,
+         *     or was recorded (as h.waitStatus) by a previous operation
+         *     (note: this uses sign-check of waitStatus because
+         *      PROPAGATE status may transition to SIGNAL.)
+         * and
+         *   The next node is waiting in shared mode,
+         *     or we don't know, because it appears null
+         *
+         * The conservatism in both of these checks may cause
+         * unnecessary wake-ups, but only when there are multiple
+         * racing acquires/releases, so most need signals now or soon
+         * anyway.
+         */
+        if (propagate > 0 || h == null || h.waitStatus < 0) {
+            Node s = node.next;
+            if (s == null || s.isShared())
+                doReleaseShared();
+        }
+    }
+
+    // Utilities for various versions of acquire
+
+    /**
+     * Cancels an ongoing attempt to acquire.
+     *
+     * @param node the node
+     */
+    private void cancelAcquire(Node node) {
+        // Ignore if node doesn't exist
+        if (node == null)
+            return;
+
+        node.thread = null;
+
+        // Skip cancelled predecessors
+        Node pred = node.prev;
+        while (pred.waitStatus > 0)
+            node.prev = pred = pred.prev;
+
+        // predNext is the apparent node to unsplice. CASes below will
+        // fail if not, in which case, we lost race vs another cancel
+        // or signal, so no further action is necessary.
+        Node predNext = pred.next;
+
+        // Can use unconditional write instead of CAS here.
+        // After this atomic step, other Nodes can skip past us.
+        // Before, we are free of interference from other threads.
+        node.waitStatus = Node.CANCELLED;
+
+        // If we are the tail, remove ourselves.
+        if (node == tail && compareAndSetTail(node, pred)) {
+            compareAndSetNext(pred, predNext, null);
+        } else {
+            // If successor needs signal, try to set pred's next-link
+            // so it will get one. Otherwise wake it up to propagate.
+            int ws;
+            if (pred != head &&
+                ((ws = pred.waitStatus) == Node.SIGNAL ||
+                 (ws <= 0 && compareAndSetWaitStatus(pred, ws, Node.SIGNAL))) &&
+                pred.thread != null) {
+                Node next = node.next;
+                if (next != null && next.waitStatus <= 0)
+                    compareAndSetNext(pred, predNext, next);
+            } else {
+                unparkSuccessor(node);
+            }
+
+            node.next = node; // help GC
+        }
+    }
+
+    /**
+     * Checks and updates status for a node that failed to acquire.
+     * Returns true if thread should block. This is the main signal
+     * control in all acquire loops.  Requires that pred == node.prev
+     *
+     * @param pred node's predecessor holding status
+     * @param node the node
+     * @return {@code true} if thread should block
+     */
+    private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
+        int ws = pred.waitStatus;
+        if (ws == Node.SIGNAL)
+            /*
+             * This node has already set status asking a release
+             * to signal it, so it can safely park.
+             */
+            return true;
+        if (ws > 0) {
+            /*
+             * Predecessor was cancelled. Skip over predecessors and
+             * indicate retry.
+             */
+            do {
+                node.prev = pred = pred.prev;
+            } while (pred.waitStatus > 0);
+            pred.next = node;
+        } else {
+            /*
+             * waitStatus must be 0 or PROPAGATE.  Indicate that we
+             * need a signal, but don't park yet.  Caller will need to
+             * retry to make sure it cannot acquire before parking.
+             */
+            compareAndSetWaitStatus(pred, ws, Node.SIGNAL);
+        }
+        return false;
+    }
+
+    /**
+     * Convenience method to interrupt current thread.
+     */
+    private static void selfInterrupt() {
+        Thread.currentThread().interrupt();
+    }
+
+    /**
+     * Convenience method to park and then check if interrupted
+     *
+     * @return {@code true} if interrupted
+     */
+    private final boolean parkAndCheckInterrupt() {
+        LockSupport.park();
+        return Thread.interrupted();
+    }
+
+    /*
+     * Various flavors of acquire, varying in exclusive/shared and
+     * control modes.  Each is mostly the same, but annoyingly
+     * different.  Only a little bit of factoring is possible due to
+     * interactions of exception mechanics (including ensuring that we
+     * cancel if tryAcquire throws exception) and other control, at
+     * least not without hurting performance too much.
+     */
+
+    /**
+     * Acquires in exclusive uninterruptible mode for thread already in
+     * queue. Used by condition wait methods as well as acquire.
+     *
+     * @param node the node
+     * @param arg the acquire argument
+     * @return {@code true} if interrupted while waiting
+     */
+    final boolean acquireQueued(final Node node, long arg) {
+        boolean failed = true;
+        try {
+            boolean interrupted = false;
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head && tryAcquire(arg)) {
+                    setHead(node);
+                    p.next = null; // help GC
+                    failed = false;
+                    return interrupted;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    parkAndCheckInterrupt())
+                    interrupted = true;
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    /**
+     * Acquires in exclusive interruptible mode.
+     * @param arg the acquire argument
+     */
+    private void doAcquireInterruptibly(long arg)
+        throws InterruptedException {
+        final Node node = addWaiter(Node.EXCLUSIVE);
+        boolean failed = true;
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head && tryAcquire(arg)) {
+                    setHead(node);
+                    p.next = null; // help GC
+                    failed = false;
+                    return;
+                }
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    parkAndCheckInterrupt())
+                    throw new InterruptedException();
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    /**
+     * Acquires in exclusive timed mode.
+     *
+     * @param arg the acquire argument
+     * @param nanosTimeout max wait time
+     * @return {@code true} if acquired
+     */
+    private boolean doAcquireNanos(long arg, long nanosTimeout)
+        throws InterruptedException {
+        long lastTime = System.nanoTime();
+        final Node node = addWaiter(Node.EXCLUSIVE);
+        boolean failed = true;
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head && tryAcquire(arg)) {
+                    setHead(node);
+                    p.next = null; // help GC
+                    failed = false;
+                    return true;
+                }
+                if (nanosTimeout <= 0)
+                    return false;
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    nanosTimeout > spinForTimeoutThreshold)
+                    LockSupport.parkNanos(nanosTimeout);
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+                if (Thread.interrupted())
+                    throw new InterruptedException();
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    /**
+     * Acquires in shared uninterruptible mode.
+     * @param arg the acquire argument
+     */
+    private void doAcquireShared(long arg) {
+        final Node node = addWaiter(Node.SHARED);
+        boolean failed = true;
+        try {
+            boolean interrupted = false;
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head) {
+                    long r = tryAcquireShared(arg);
+                    if (r >= 0) {
+                        setHeadAndPropagate(node, r);
+                        p.next = null; // help GC
+                        if (interrupted)
+                            selfInterrupt();
+                        failed = false;
+                        return;
+                    }
+                }
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    parkAndCheckInterrupt())
+                    interrupted = true;
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    /**
+     * Acquires in shared interruptible mode.
+     * @param arg the acquire argument
+     */
+    private void doAcquireSharedInterruptibly(long arg)
+        throws InterruptedException {
+        final Node node = addWaiter(Node.SHARED);
+        boolean failed = true;
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head) {
+                    long r = tryAcquireShared(arg);
+                    if (r >= 0) {
+                        setHeadAndPropagate(node, r);
+                        p.next = null; // help GC
+                        failed = false;
+                        return;
+                    }
+                }
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    parkAndCheckInterrupt())
+                    throw new InterruptedException();
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    /**
+     * Acquires in shared timed mode.
+     *
+     * @param arg the acquire argument
+     * @param nanosTimeout max wait time
+     * @return {@code true} if acquired
+     */
+    private boolean doAcquireSharedNanos(long arg, long nanosTimeout)
+        throws InterruptedException {
+
+        long lastTime = System.nanoTime();
+        final Node node = addWaiter(Node.SHARED);
+        boolean failed = true;
+        try {
+            for (;;) {
+                final Node p = node.predecessor();
+                if (p == head) {
+                    long r = tryAcquireShared(arg);
+                    if (r >= 0) {
+                        setHeadAndPropagate(node, r);
+                        p.next = null; // help GC
+                        failed = false;
+                        return true;
+                    }
+                }
+                if (nanosTimeout <= 0)
+                    return false;
+                if (shouldParkAfterFailedAcquire(p, node) &&
+                    nanosTimeout > spinForTimeoutThreshold)
+                    LockSupport.parkNanos(nanosTimeout);
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+                if (Thread.interrupted())
+                    throw new InterruptedException();
+            }
+        } finally {
+            if (failed)
+                cancelAcquire(node);
+        }
+    }
+
+    // Main exported methods
+
+    /**
+     * Attempts to acquire in exclusive mode. This method should query
+     * if the state of the object permits it to be acquired in the
+     * exclusive mode, and if so to acquire it.
+     *
+     * <p>This method is always invoked by the thread performing
+     * acquire.  If this method reports failure, the acquire method
+     * may queue the thread, if it is not already queued, until it is
+     * signalled by a release from some other thread. This can be used
+     * to implement method {@link Lock#tryLock()}.
+     *
+     * <p>The default
+     * implementation throws {@link UnsupportedOperationException}.
+     *
+     * @param arg the acquire argument. This value is always the one
+     *        passed to an acquire method, or is the value saved on entry
+     *        to a condition wait.  The value is otherwise uninterpreted
+     *        and can represent anything you like.
+     * @return {@code true} if successful. Upon success, this object has
+     *         been acquired.
+     * @throws IllegalMonitorStateException if acquiring would place this
+     *         synchronizer in an illegal state. This exception must be
+     *         thrown in a consistent fashion for synchronization to work
+     *         correctly.
+     * @throws UnsupportedOperationException if exclusive mode is not supported
+     */
+    protected boolean tryAcquire(long arg) {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Attempts to set the state to reflect a release in exclusive
+     * mode.
+     *
+     * <p>This method is always invoked by the thread performing release.
+     *
+     * <p>The default implementation throws
+     * {@link UnsupportedOperationException}.
+     *
+     * @param arg the release argument. This value is always the one
+     *        passed to a release method, or the current state value upon
+     *        entry to a condition wait.  The value is otherwise
+     *        uninterpreted and can represent anything you like.
+     * @return {@code true} if this object is now in a fully released
+     *         state, so that any waiting threads may attempt to acquire;
+     *         and {@code false} otherwise.
+     * @throws IllegalMonitorStateException if releasing would place this
+     *         synchronizer in an illegal state. This exception must be
+     *         thrown in a consistent fashion for synchronization to work
+     *         correctly.
+     * @throws UnsupportedOperationException if exclusive mode is not supported
+     */
+    protected boolean tryRelease(long arg) {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Attempts to acquire in shared mode. This method should query if
+     * the state of the object permits it to be acquired in the shared
+     * mode, and if so to acquire it.
+     *
+     * <p>This method is always invoked by the thread performing
+     * acquire.  If this method reports failure, the acquire method
+     * may queue the thread, if it is not already queued, until it is
+     * signalled by a release from some other thread.
+     *
+     * <p>The default implementation throws {@link
+     * UnsupportedOperationException}.
+     *
+     * @param arg the acquire argument. This value is always the one
+     *        passed to an acquire method, or is the value saved on entry
+     *        to a condition wait.  The value is otherwise uninterpreted
+     *        and can represent anything you like.
+     * @return a negative value on failure; zero if acquisition in shared
+     *         mode succeeded but no subsequent shared-mode acquire can
+     *         succeed; and a positive value if acquisition in shared
+     *         mode succeeded and subsequent shared-mode acquires might
+     *         also succeed, in which case a subsequent waiting thread
+     *         must check availability. (Support for three different
+     *         return values enables this method to be used in contexts
+     *         where acquires only sometimes act exclusively.)  Upon
+     *         success, this object has been acquired.
+     * @throws IllegalMonitorStateException if acquiring would place this
+     *         synchronizer in an illegal state. This exception must be
+     *         thrown in a consistent fashion for synchronization to work
+     *         correctly.
+     * @throws UnsupportedOperationException if shared mode is not supported
+     */
+    protected long tryAcquireShared(long arg) {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Attempts to set the state to reflect a release in shared mode.
+     *
+     * <p>This method is always invoked by the thread performing release.
+     *
+     * <p>The default implementation throws
+     * {@link UnsupportedOperationException}.
+     *
+     * @param arg the release argument. This value is always the one
+     *        passed to a release method, or the current state value upon
+     *        entry to a condition wait.  The value is otherwise
+     *        uninterpreted and can represent anything you like.
+     * @return {@code true} if this release of shared mode may permit a
+     *         waiting acquire (shared or exclusive) to succeed; and
+     *         {@code false} otherwise
+     * @throws IllegalMonitorStateException if releasing would place this
+     *         synchronizer in an illegal state. This exception must be
+     *         thrown in a consistent fashion for synchronization to work
+     *         correctly.
+     * @throws UnsupportedOperationException if shared mode is not supported
+     */
+    protected boolean tryReleaseShared(long arg) {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Returns {@code true} if synchronization is held exclusively with
+     * respect to the current (calling) thread.  This method is invoked
+     * upon each call to a non-waiting {@link ConditionObject} method.
+     * (Waiting methods instead invoke {@link #release}.)
+     *
+     * <p>The default implementation throws {@link
+     * UnsupportedOperationException}. This method is invoked
+     * internally only within {@link ConditionObject} methods, so need
+     * not be defined if conditions are not used.
+     *
+     * @return {@code true} if synchronization is held exclusively;
+     *         {@code false} otherwise
+     * @throws UnsupportedOperationException if conditions are not supported
+     */
+    protected boolean isHeldExclusively() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Acquires in exclusive mode, ignoring interrupts.  Implemented
+     * by invoking at least once {@link #tryAcquire},
+     * returning on success.  Otherwise the thread is queued, possibly
+     * repeatedly blocking and unblocking, invoking {@link
+     * #tryAcquire} until success.  This method can be used
+     * to implement method {@link Lock#lock}.
+     *
+     * @param arg the acquire argument.  This value is conveyed to
+     *        {@link #tryAcquire} but is otherwise uninterpreted and
+     *        can represent anything you like.
+     */
+    public final void acquire(long arg) {
+        if (!tryAcquire(arg) &&
+            acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
+            selfInterrupt();
+    }
+
+    /**
+     * Acquires in exclusive mode, aborting if interrupted.
+     * Implemented by first checking interrupt status, then invoking
+     * at least once {@link #tryAcquire}, returning on
+     * success.  Otherwise the thread is queued, possibly repeatedly
+     * blocking and unblocking, invoking {@link #tryAcquire}
+     * until success or the thread is interrupted.  This method can be
+     * used to implement method {@link Lock#lockInterruptibly}.
+     *
+     * @param arg the acquire argument.  This value is conveyed to
+     *        {@link #tryAcquire} but is otherwise uninterpreted and
+     *        can represent anything you like.
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public final void acquireInterruptibly(long arg) throws InterruptedException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        if (!tryAcquire(arg))
+            doAcquireInterruptibly(arg);
+    }
+
+    /**
+     * Attempts to acquire in exclusive mode, aborting if interrupted,
+     * and failing if the given timeout elapses.  Implemented by first
+     * checking interrupt status, then invoking at least once {@link
+     * #tryAcquire}, returning on success.  Otherwise, the thread is
+     * queued, possibly repeatedly blocking and unblocking, invoking
+     * {@link #tryAcquire} until success or the thread is interrupted
+     * or the timeout elapses.  This method can be used to implement
+     * method {@link Lock#tryLock(long, TimeUnit)}.
+     *
+     * @param arg the acquire argument.  This value is conveyed to
+     *        {@link #tryAcquire} but is otherwise uninterpreted and
+     *        can represent anything you like.
+     * @param nanosTimeout the maximum number of nanoseconds to wait
+     * @return {@code true} if acquired; {@code false} if timed out
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public final boolean tryAcquireNanos(long arg, long nanosTimeout) throws InterruptedException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        return tryAcquire(arg) ||
+            doAcquireNanos(arg, nanosTimeout);
+    }
+
+    /**
+     * Releases in exclusive mode.  Implemented by unblocking one or
+     * more threads if {@link #tryRelease} returns true.
+     * This method can be used to implement method {@link Lock#unlock}.
+     *
+     * @param arg the release argument.  This value is conveyed to
+     *        {@link #tryRelease} but is otherwise uninterpreted and
+     *        can represent anything you like.
+     * @return the value returned from {@link #tryRelease}
+     */
+    public final boolean release(long arg) {
+        if (tryRelease(arg)) {
+            Node h = head;
+            if (h != null && h.waitStatus != 0)
+                unparkSuccessor(h);
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * Acquires in shared mode, ignoring interrupts.  Implemented by
+     * first invoking at least once {@link #tryAcquireShared},
+     * returning on success.  Otherwise the thread is queued, possibly
+     * repeatedly blocking and unblocking, invoking {@link
+     * #tryAcquireShared} until success.
+     *
+     * @param arg the acquire argument.  This value is conveyed to
+     *        {@link #tryAcquireShared} but is otherwise uninterpreted
+     *        and can represent anything you like.
+     */
+    public final void acquireShared(long arg) {
+        if (tryAcquireShared(arg) < 0)
+            doAcquireShared(arg);
+    }
+
+    /**
+     * Acquires in shared mode, aborting if interrupted.  Implemented
+     * by first checking interrupt status, then invoking at least once
+     * {@link #tryAcquireShared}, returning on success.  Otherwise the
+     * thread is queued, possibly repeatedly blocking and unblocking,
+     * invoking {@link #tryAcquireShared} until success or the thread
+     * is interrupted.
+     * @param arg the acquire argument
+     * This value is conveyed to {@link #tryAcquireShared} but is
+     * otherwise uninterpreted and can represent anything
+     * you like.
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public final void acquireSharedInterruptibly(long arg) throws InterruptedException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        if (tryAcquireShared(arg) < 0)
+            doAcquireSharedInterruptibly(arg);
+    }
+
+    /**
+     * Attempts to acquire in shared mode, aborting if interrupted, and
+     * failing if the given timeout elapses.  Implemented by first
+     * checking interrupt status, then invoking at least once {@link
+     * #tryAcquireShared}, returning on success.  Otherwise, the
+     * thread is queued, possibly repeatedly blocking and unblocking,
+     * invoking {@link #tryAcquireShared} until success or the thread
+     * is interrupted or the timeout elapses.
+     *
+     * @param arg the acquire argument.  This value is conveyed to
+     *        {@link #tryAcquireShared} but is otherwise uninterpreted
+     *        and can represent anything you like.
+     * @param nanosTimeout the maximum number of nanoseconds to wait
+     * @return {@code true} if acquired; {@code false} if timed out
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout) throws InterruptedException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        return tryAcquireShared(arg) >= 0 ||
+            doAcquireSharedNanos(arg, nanosTimeout);
+    }
+
+    /**
+     * Releases in shared mode.  Implemented by unblocking one or more
+     * threads if {@link #tryReleaseShared} returns true.
+     *
+     * @param arg the release argument.  This value is conveyed to
+     *        {@link #tryReleaseShared} but is otherwise uninterpreted
+     *        and can represent anything you like.
+     * @return the value returned from {@link #tryReleaseShared}
+     */
+    public final boolean releaseShared(long arg) {
+        if (tryReleaseShared(arg)) {
+            doReleaseShared();
+            return true;
+        }
+        return false;
+    }
+
+    // Queue inspection methods
+
+    /**
+     * Queries whether any threads are waiting to acquire. Note that
+     * because cancellations due to interrupts and timeouts may occur
+     * at any time, a {@code true} return does not guarantee that any
+     * other thread will ever acquire.
+     *
+     * <p>In this implementation, this operation returns in
+     * constant time.
+     *
+     * @return {@code true} if there may be other threads waiting to acquire
+     */
+    public final boolean hasQueuedThreads() {
+        return head != tail;
+    }
+
+    /**
+     * Queries whether any threads have ever contended to acquire this
+     * synchronizer; that is if an acquire method has ever blocked.
+     *
+     * <p>In this implementation, this operation returns in
+     * constant time.
+     *
+     * @return {@code true} if there has ever been contention
+     */
+    public final boolean hasContended() {
+        return head != null;
+    }
+
+    /**
+     * Returns the first (longest-waiting) thread in the queue, or
+     * {@code null} if no threads are currently queued.
+     *
+     * <p>In this implementation, this operation normally returns in
+     * constant time, but may iterate upon contention if other threads are
+     * concurrently modifying the queue.
+     *
+     * @return the first (longest-waiting) thread in the queue, or
+     *         {@code null} if no threads are currently queued
+     */
+    public final Thread getFirstQueuedThread() {
+        // handle only fast path, else relay
+        return (head == tail) ? null : fullGetFirstQueuedThread();
+    }
+
+    /**
+     * Version of getFirstQueuedThread called when fastpath fails
+     */
+    private Thread fullGetFirstQueuedThread() {
+        /*
+         * The first node is normally head.next. Try to get its
+         * thread field, ensuring consistent reads: If thread
+         * field is nulled out or s.prev is no longer head, then
+         * some other thread(s) concurrently performed setHead in
+         * between some of our reads. We try this twice before
+         * resorting to traversal.
+         */
+        Node h, s;
+        Thread st;
+        if (((h = head) != null && (s = h.next) != null &&
+             s.prev == head && (st = s.thread) != null) ||
+            ((h = head) != null && (s = h.next) != null &&
+             s.prev == head && (st = s.thread) != null))
+            return st;
+
+        /*
+         * Head's next field might not have been set yet, or may have
+         * been unset after setHead. So we must check to see if tail
+         * is actually first node. If not, we continue on, safely
+         * traversing from tail back to head to find first,
+         * guaranteeing termination.
+         */
+
+        Node t = tail;
+        Thread firstThread = null;
+        while (t != null && t != head) {
+            Thread tt = t.thread;
+            if (tt != null)
+                firstThread = tt;
+            t = t.prev;
+        }
+        return firstThread;
+    }
+
+    /**
+     * Returns true if the given thread is currently queued.
+     *
+     * <p>This implementation traverses the queue to determine
+     * presence of the given thread.
+     *
+     * @param thread the thread
+     * @return {@code true} if the given thread is on the queue
+     * @throws NullPointerException if the thread is null
+     */
+    public final boolean isQueued(Thread thread) {
+        if (thread == null)
+            throw new NullPointerException();
+        for (Node p = tail; p != null; p = p.prev)
+            if (p.thread == thread)
+                return true;
+        return false;
+    }
+
+    /**
+     * Returns {@code true} if the apparent first queued thread, if one
+     * exists, is waiting in exclusive mode.  If this method returns
+     * {@code true}, and the current thread is attempting to acquire in
+     * shared mode (that is, this method is invoked from {@link
+     * #tryAcquireShared}) then it is guaranteed that the current thread
+     * is not the first queued thread.  Used only as a heuristic in
+     * ReentrantReadWriteLock.
+     */
+    final boolean apparentlyFirstQueuedIsExclusive() {
+        Node h, s;
+        return (h = head) != null &&
+            (s = h.next)  != null &&
+            !s.isShared()         &&
+            s.thread != null;
+    }
+
+    /**
+     * Queries whether any threads have been waiting to acquire longer
+     * than the current thread.
+     *
+     * <p>An invocation of this method is equivalent to (but may be
+     * more efficient than):
+     *  <pre> {@code
+     * getFirstQueuedThread() != Thread.currentThread() &&
+     * hasQueuedThreads()}</pre>
+     *
+     * <p>Note that because cancellations due to interrupts and
+     * timeouts may occur at any time, a {@code true} return does not
+     * guarantee that some other thread will acquire before the current
+     * thread.  Likewise, it is possible for another thread to win a
+     * race to enqueue after this method has returned {@code false},
+     * due to the queue being empty.
+     *
+     * <p>This method is designed to be used by a fair synchronizer to
+     * avoid <a href="AbstractQueuedSynchronizer#barging">barging</a>.
+     * Such a synchronizer's {@link #tryAcquire} method should return
+     * {@code false}, and its {@link #tryAcquireShared} method should
+     * return a negative value, if this method returns {@code true}
+     * (unless this is a reentrant acquire).  For example, the {@code
+     * tryAcquire} method for a fair, reentrant, exclusive mode
+     * synchronizer might look like this:
+     *
+     *  <pre> {@code
+     * protected boolean tryAcquire(int arg) {
+     *   if (isHeldExclusively()) {
+     *     // A reentrant acquire; increment hold count
+     *     return true;
+     *   } else if (hasQueuedPredecessors()) {
+     *     return false;
+     *   } else {
+     *     // try to acquire normally
+     *   }
+     * }}</pre>
+     *
+     * @return {@code true} if there is a queued thread preceding the
+     *         current thread, and {@code false} if the current thread
+     *         is at the head of the queue or the queue is empty
+     */
+    final boolean hasQueuedPredecessors() {
+        // The correctness of this depends on head being initialized
+        // before tail and on head.next being accurate if the current
+        // thread is first in queue.
+        Node t = tail; // Read fields in reverse initialization order
+        Node h = head;
+        Node s;
+        return h != t &&
+            ((s = h.next) == null || s.thread != Thread.currentThread());
+    }
+
+
+    // Instrumentation and monitoring methods
+
+    /**
+     * Returns an estimate of the number of threads waiting to
+     * acquire.  The value is only an estimate because the number of
+     * threads may change dynamically while this method traverses
+     * internal data structures.  This method is designed for use in
+     * monitoring system state, not for synchronization
+     * control.
+     *
+     * @return the estimated number of threads waiting to acquire
+     */
+    public final int getQueueLength() {
+        int n = 0;
+        for (Node p = tail; p != null; p = p.prev) {
+            if (p.thread != null)
+                ++n;
+        }
+        return n;
+    }
+
+    /**
+     * Returns a collection containing threads that may be waiting to
+     * acquire.  Because the actual set of threads may change
+     * dynamically while constructing this result, the returned
+     * collection is only a best-effort estimate.  The elements of the
+     * returned collection are in no particular order.  This method is
+     * designed to facilitate construction of subclasses that provide
+     * more extensive monitoring facilities.
+     *
+     * @return the collection of threads
+     */
+    public final Collection<Thread> getQueuedThreads() {
+        ArrayList<Thread> list = new ArrayList<Thread>();
+        for (Node p = tail; p != null; p = p.prev) {
+            Thread t = p.thread;
+            if (t != null)
+                list.add(t);
+        }
+        return list;
+    }
+
+    /**
+     * Returns a collection containing threads that may be waiting to
+     * acquire in exclusive mode. This has the same properties
+     * as {@link #getQueuedThreads} except that it only returns
+     * those threads waiting due to an exclusive acquire.
+     *
+     * @return the collection of threads
+     */
+    public final Collection<Thread> getExclusiveQueuedThreads() {
+        ArrayList<Thread> list = new ArrayList<Thread>();
+        for (Node p = tail; p != null; p = p.prev) {
+            if (!p.isShared()) {
+                Thread t = p.thread;
+                if (t != null)
+                    list.add(t);
+            }
+        }
+        return list;
+    }
+
+    /**
+     * Returns a collection containing threads that may be waiting to
+     * acquire in shared mode. This has the same properties
+     * as {@link #getQueuedThreads} except that it only returns
+     * those threads waiting due to a shared acquire.
+     *
+     * @return the collection of threads
+     */
+    public final Collection<Thread> getSharedQueuedThreads() {
+        ArrayList<Thread> list = new ArrayList<Thread>();
+        for (Node p = tail; p != null; p = p.prev) {
+            if (p.isShared()) {
+                Thread t = p.thread;
+                if (t != null)
+                    list.add(t);
+            }
+        }
+        return list;
+    }
+
+    /**
+     * Returns a string identifying this synchronizer, as well as its state.
+     * The state, in brackets, includes the String {@code "State ="}
+     * followed by the current value of {@link #getState}, and either
+     * {@code "nonempty"} or {@code "empty"} depending on whether the
+     * queue is empty.
+     *
+     * @return a string identifying this synchronizer, as well as its state
+     */
+    public String toString() {
+        long s = getState();
+        String q  = hasQueuedThreads() ? "non" : "";
+        return super.toString() +
+            "[State = " + s + ", " + q + "empty queue]";
+    }
+
+
+    // Internal support methods for Conditions
+
+    /**
+     * Returns true if a node, always one that was initially placed on
+     * a condition queue, is now waiting to reacquire on sync queue.
+     * @param node the node
+     * @return true if is reacquiring
+     */
+    final boolean isOnSyncQueue(Node node) {
+        if (node.waitStatus == Node.CONDITION || node.prev == null)
+            return false;
+        if (node.next != null) // If has successor, it must be on queue
+            return true;
+        /*
+         * node.prev can be non-null, but not yet on queue because
+         * the CAS to place it on queue can fail. So we have to
+         * traverse from tail to make sure it actually made it.  It
+         * will always be near the tail in calls to this method, and
+         * unless the CAS failed (which is unlikely), it will be
+         * there, so we hardly ever traverse much.
+         */
+        return findNodeFromTail(node);
+    }
+
+    /**
+     * Returns true if node is on sync queue by searching backwards from tail.
+     * Called only when needed by isOnSyncQueue.
+     * @return true if present
+     */
+    private boolean findNodeFromTail(Node node) {
+        Node t = tail;
+        for (;;) {
+            if (t == node)
+                return true;
+            if (t == null)
+                return false;
+            t = t.prev;
+        }
+    }
+
+    /**
+     * Transfers a node from a condition queue onto sync queue.
+     * Returns true if successful.
+     * @param node the node
+     * @return true if successfully transferred (else the node was
+     * cancelled before signal).
+     */
+    final boolean transferForSignal(Node node) {
+        /*
+         * If cannot change waitStatus, the node has been cancelled.
+         */
+        if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
+            return false;
+
+        /*
+         * Splice onto queue and try to set waitStatus of predecessor to
+         * indicate that thread is (probably) waiting. If cancelled or
+         * attempt to set waitStatus fails, wake up to resync (in which
+         * case the waitStatus can be transiently and harmlessly wrong).
+         */
+        Node p = enq(node);
+        int ws = p.waitStatus;
+        if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
+            LockSupport.unpark(node.thread);
+        return true;
+    }
+
+    /**
+     * Transfers node, if necessary, to sync queue after a cancelled
+     * wait. Returns true if thread was cancelled before being
+     * signalled.
+     * @param current the waiting thread
+     * @param node its node
+     * @return true if cancelled before the node was signalled
+     */
+    final boolean transferAfterCancelledWait(Node node) {
+        if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
+            enq(node);
+            return true;
+        }
+        /*
+         * If we lost out to a signal(), then we can't proceed
+         * until it finishes its enq().  Cancelling during an
+         * incomplete transfer is both rare and transient, so just
+         * spin.
+         */
+        while (!isOnSyncQueue(node))
+            Thread.yield();
+        return false;
+    }
+
+    /**
+     * Invokes release with current state value; returns saved state.
+     * Cancels node and throws exception on failure.
+     * @param node the condition node for this wait
+     * @return previous sync state
+     */
+    final long fullyRelease(Node node) {
+        boolean failed = true;
+        try {
+            long savedState = getState();
+            if (release(savedState)) {
+                failed = false;
+                return savedState;
+            } else {
+                throw new IllegalMonitorStateException();
+            }
+        } finally {
+            if (failed)
+                node.waitStatus = Node.CANCELLED;
+        }
+    }
+
+    // Instrumentation methods for conditions
+
+    /**
+     * Queries whether the given ConditionObject
+     * uses this synchronizer as its lock.
+     *
+     * @param condition the condition
+     * @return <tt>true</tt> if owned
+     * @throws NullPointerException if the condition is null
+     */
+    public final boolean owns(ConditionObject condition) {
+        if (condition == null)
+            throw new NullPointerException();
+        return condition.isOwnedBy(this);
+    }
+
+    /**
+     * Queries whether any threads are waiting on the given condition
+     * associated with this synchronizer. Note that because timeouts
+     * and interrupts may occur at any time, a <tt>true</tt> return
+     * does not guarantee that a future <tt>signal</tt> will awaken
+     * any threads.  This method is designed primarily for use in
+     * monitoring of the system state.
+     *
+     * @param condition the condition
+     * @return <tt>true</tt> if there are any waiting threads
+     * @throws IllegalMonitorStateException if exclusive synchronization
+     *         is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this synchronizer
+     * @throws NullPointerException if the condition is null
+     */
+    public final boolean hasWaiters(ConditionObject condition) {
+        if (!owns(condition))
+            throw new IllegalArgumentException("Not owner");
+        return condition.hasWaiters();
+    }
+
+    /**
+     * Returns an estimate of the number of threads waiting on the
+     * given condition associated with this synchronizer. Note that
+     * because timeouts and interrupts may occur at any time, the
+     * estimate serves only as an upper bound on the actual number of
+     * waiters.  This method is designed for use in monitoring of the
+     * system state, not for synchronization control.
+     *
+     * @param condition the condition
+     * @return the estimated number of waiting threads
+     * @throws IllegalMonitorStateException if exclusive synchronization
+     *         is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this synchronizer
+     * @throws NullPointerException if the condition is null
+     */
+    public final int getWaitQueueLength(ConditionObject condition) {
+        if (!owns(condition))
+            throw new IllegalArgumentException("Not owner");
+        return condition.getWaitQueueLength();
+    }
+
+    /**
+     * Returns a collection containing those threads that may be
+     * waiting on the given condition associated with this
+     * synchronizer.  Because the actual set of threads may change
+     * dynamically while constructing this result, the returned
+     * collection is only a best-effort estimate. The elements of the
+     * returned collection are in no particular order.
+     *
+     * @param condition the condition
+     * @return the collection of threads
+     * @throws IllegalMonitorStateException if exclusive synchronization
+     *         is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this synchronizer
+     * @throws NullPointerException if the condition is null
+     */
+    public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
+        if (!owns(condition))
+            throw new IllegalArgumentException("Not owner");
+        return condition.getWaitingThreads();
+    }
+
+    /**
+     * Condition implementation for a {@link
+     * AbstractQueuedLongSynchronizer} serving as the basis of a {@link
+     * Lock} implementation.
+     *
+     * <p>Method documentation for this class describes mechanics,
+     * not behavioral specifications from the point of view of Lock
+     * and Condition users. Exported versions of this class will in
+     * general need to be accompanied by documentation describing
+     * condition semantics that rely on those of the associated
+     * <tt>AbstractQueuedLongSynchronizer</tt>.
+     *
+     * <p>This class is Serializable, but all fields are transient,
+     * so deserialized conditions have no waiters.
+     *
+     * @since 1.6
+     */
+    public class ConditionObject implements Condition, java.io.Serializable {
+        private static final long serialVersionUID = 1173984872572414699L;
+        /** First node of condition queue. */
+        private transient Node firstWaiter;
+        /** Last node of condition queue. */
+        private transient Node lastWaiter;
+
+        /**
+         * Creates a new <tt>ConditionObject</tt> instance.
+         */
+        public ConditionObject() { }
+
+        // Internal methods
+
+        /**
+         * Adds a new waiter to wait queue.
+         * @return its new wait node
+         */
+        private Node addConditionWaiter() {
+            Node t = lastWaiter;
+            // If lastWaiter is cancelled, clean out.
+            if (t != null && t.waitStatus != Node.CONDITION) {
+                unlinkCancelledWaiters();
+                t = lastWaiter;
+            }
+            Node node = new Node(Thread.currentThread(), Node.CONDITION);
+            if (t == null)
+                firstWaiter = node;
+            else
+                t.nextWaiter = node;
+            lastWaiter = node;
+            return node;
+        }
+
+        /**
+         * Removes and transfers nodes until hit non-cancelled one or
+         * null. Split out from signal in part to encourage compilers
+         * to inline the case of no waiters.
+         * @param first (non-null) the first node on condition queue
+         */
+        private void doSignal(Node first) {
+            do {
+                if ( (firstWaiter = first.nextWaiter) == null)
+                    lastWaiter = null;
+                first.nextWaiter = null;
+            } while (!transferForSignal(first) &&
+                     (first = firstWaiter) != null);
+        }
+
+        /**
+         * Removes and transfers all nodes.
+         * @param first (non-null) the first node on condition queue
+         */
+        private void doSignalAll(Node first) {
+            lastWaiter = firstWaiter = null;
+            do {
+                Node next = first.nextWaiter;
+                first.nextWaiter = null;
+                transferForSignal(first);
+                first = next;
+            } while (first != null);
+        }
+
+        /**
+         * Unlinks cancelled waiter nodes from condition queue.
+         * Called only while holding lock. This is called when
+         * cancellation occurred during condition wait, and upon
+         * insertion of a new waiter when lastWaiter is seen to have
+         * been cancelled. This method is needed to avoid garbage
+         * retention in the absence of signals. So even though it may
+         * require a full traversal, it comes into play only when
+         * timeouts or cancellations occur in the absence of
+         * signals. It traverses all nodes rather than stopping at a
+         * particular target to unlink all pointers to garbage nodes
+         * without requiring many re-traversals during cancellation
+         * storms.
+         */
+        private void unlinkCancelledWaiters() {
+            Node t = firstWaiter;
+            Node trail = null;
+            while (t != null) {
+                Node next = t.nextWaiter;
+                if (t.waitStatus != Node.CONDITION) {
+                    t.nextWaiter = null;
+                    if (trail == null)
+                        firstWaiter = next;
+                    else
+                        trail.nextWaiter = next;
+                    if (next == null)
+                        lastWaiter = trail;
+                }
+                else
+                    trail = t;
+                t = next;
+            }
+        }
+
+        // public methods
+
+        /**
+         * Moves the longest-waiting thread, if one exists, from the
+         * wait queue for this condition to the wait queue for the
+         * owning lock.
+         *
+         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+         *         returns {@code false}
+         */
+        public final void signal() {
+            if (!isHeldExclusively())
+                throw new IllegalMonitorStateException();
+            Node first = firstWaiter;
+            if (first != null)
+                doSignal(first);
+        }
+
+        /**
+         * Moves all threads from the wait queue for this condition to
+         * the wait queue for the owning lock.
+         *
+         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+         *         returns {@code false}
+         */
+        public final void signalAll() {
+            if (!isHeldExclusively())
+                throw new IllegalMonitorStateException();
+            Node first = firstWaiter;
+            if (first != null)
+                doSignalAll(first);
+        }
+
+        /**
+         * Implements uninterruptible condition wait.
+         * <ol>
+         * <li> Save lock state returned by {@link #getState}.
+         * <li> Invoke {@link #release} with
+         *      saved state as argument, throwing
+         *      IllegalMonitorStateException if it fails.
+         * <li> Block until signalled.
+         * <li> Reacquire by invoking specialized version of
+         *      {@link #acquire} with saved state as argument.
+         * </ol>
+         */
+        public final void awaitUninterruptibly() {
+            Node node = addConditionWaiter();
+            long savedState = fullyRelease(node);
+            boolean interrupted = false;
+            while (!isOnSyncQueue(node)) {
+                LockSupport.park();
+                if (Thread.interrupted())
+                    interrupted = true;
+            }
+            if (acquireQueued(node, savedState) || interrupted)
+                selfInterrupt();
+        }
+
+        /*
+         * For interruptible waits, we need to track whether to throw
+         * InterruptedException, if interrupted while blocked on
+         * condition, versus reinterrupt current thread, if
+         * interrupted while blocked waiting to re-acquire.
+         */
+
+        /** Mode meaning to reinterrupt on exit from wait */
+        private static final int REINTERRUPT =  1;
+        /** Mode meaning to throw InterruptedException on exit from wait */
+        private static final int THROW_IE    = -1;
+
+        /**
+         * Checks for interrupt, returning THROW_IE if interrupted
+         * before signalled, REINTERRUPT if after signalled, or
+         * 0 if not interrupted.
+         */
+        private int checkInterruptWhileWaiting(Node node) {
+            return Thread.interrupted() ?
+                (transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
+                0;
+        }
+
+        /**
+         * Throws InterruptedException, reinterrupts current thread, or
+         * does nothing, depending on mode.
+         */
+        private void reportInterruptAfterWait(int interruptMode)
+            throws InterruptedException {
+            if (interruptMode == THROW_IE)
+                throw new InterruptedException();
+            else if (interruptMode == REINTERRUPT)
+                selfInterrupt();
+        }
+
+        /**
+         * Implements interruptible condition wait.
+         * <ol>
+         * <li> If current thread is interrupted, throw InterruptedException.
+         * <li> Save lock state returned by {@link #getState}.
+         * <li> Invoke {@link #release} with
+         *      saved state as argument, throwing
+         *      IllegalMonitorStateException if it fails.
+         * <li> Block until signalled or interrupted.
+         * <li> Reacquire by invoking specialized version of
+         *      {@link #acquire} with saved state as argument.
+         * <li> If interrupted while blocked in step 4, throw InterruptedException.
+         * </ol>
+         */
+        public final void await() throws InterruptedException {
+            if (Thread.interrupted())
+                throw new InterruptedException();
+            Node node = addConditionWaiter();
+            long savedState = fullyRelease(node);
+            int interruptMode = 0;
+            while (!isOnSyncQueue(node)) {
+                LockSupport.park();
+                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+                    break;
+            }
+            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+                interruptMode = REINTERRUPT;
+            if (node.nextWaiter != null) // clean up if cancelled
+                unlinkCancelledWaiters();
+            if (interruptMode != 0)
+                reportInterruptAfterWait(interruptMode);
+        }
+
+        /**
+         * Implements timed condition wait.
+         * <ol>
+         * <li> If current thread is interrupted, throw InterruptedException.
+         * <li> Save lock state returned by {@link #getState}.
+         * <li> Invoke {@link #release} with
+         *      saved state as argument, throwing
+         *      IllegalMonitorStateException if it fails.
+         * <li> Block until signalled, interrupted, or timed out.
+         * <li> Reacquire by invoking specialized version of
+         *      {@link #acquire} with saved state as argument.
+         * <li> If interrupted while blocked in step 4, throw InterruptedException.
+         * </ol>
+         */
+        public final long awaitNanos(long nanosTimeout) throws InterruptedException {
+            if (Thread.interrupted())
+                throw new InterruptedException();
+            Node node = addConditionWaiter();
+            long savedState = fullyRelease(node);
+            long lastTime = System.nanoTime();
+            int interruptMode = 0;
+            while (!isOnSyncQueue(node)) {
+                if (nanosTimeout <= 0L) {
+                    transferAfterCancelledWait(node);
+                    break;
+                }
+                LockSupport.parkNanos(nanosTimeout);
+                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+                    break;
+
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+            }
+            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+                interruptMode = REINTERRUPT;
+            if (node.nextWaiter != null)
+                unlinkCancelledWaiters();
+            if (interruptMode != 0)
+                reportInterruptAfterWait(interruptMode);
+            return nanosTimeout - (System.nanoTime() - lastTime);
+        }
+
+        /**
+         * Implements absolute timed condition wait.
+         * <ol>
+         * <li> If current thread is interrupted, throw InterruptedException.
+         * <li> Save lock state returned by {@link #getState}.
+         * <li> Invoke {@link #release} with
+         *      saved state as argument, throwing
+         *      IllegalMonitorStateException if it fails.
+         * <li> Block until signalled, interrupted, or timed out.
+         * <li> Reacquire by invoking specialized version of
+         *      {@link #acquire} with saved state as argument.
+         * <li> If interrupted while blocked in step 4, throw InterruptedException.
+         * <li> If timed out while blocked in step 4, return false, else true.
+         * </ol>
+         */
+        public final boolean awaitUntil(Date deadline) throws InterruptedException {
+            if (deadline == null)
+                throw new NullPointerException();
+            long abstime = deadline.getTime();
+            if (Thread.interrupted())
+                throw new InterruptedException();
+            Node node = addConditionWaiter();
+            long savedState = fullyRelease(node);
+            boolean timedout = false;
+            int interruptMode = 0;
+            while (!isOnSyncQueue(node)) {
+                if (System.currentTimeMillis() > abstime) {
+                    timedout = transferAfterCancelledWait(node);
+                    break;
+                }
+                LockSupport.parkUntil(abstime);
+                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+                    break;
+            }
+            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+                interruptMode = REINTERRUPT;
+            if (node.nextWaiter != null)
+                unlinkCancelledWaiters();
+            if (interruptMode != 0)
+                reportInterruptAfterWait(interruptMode);
+            return !timedout;
+        }
+
+        /**
+         * Implements timed condition wait.
+         * <ol>
+         * <li> If current thread is interrupted, throw InterruptedException.
+         * <li> Save lock state returned by {@link #getState}.
+         * <li> Invoke {@link #release} with
+         *      saved state as argument, throwing
+         *      IllegalMonitorStateException if it fails.
+         * <li> Block until signalled, interrupted, or timed out.
+         * <li> Reacquire by invoking specialized version of
+         *      {@link #acquire} with saved state as argument.
+         * <li> If interrupted while blocked in step 4, throw InterruptedException.
+         * <li> If timed out while blocked in step 4, return false, else true.
+         * </ol>
+         */
+        public final boolean await(long time, TimeUnit unit) throws InterruptedException {
+            if (unit == null)
+                throw new NullPointerException();
+            long nanosTimeout = unit.toNanos(time);
+            if (Thread.interrupted())
+                throw new InterruptedException();
+            Node node = addConditionWaiter();
+            long savedState = fullyRelease(node);
+            long lastTime = System.nanoTime();
+            boolean timedout = false;
+            int interruptMode = 0;
+            while (!isOnSyncQueue(node)) {
+                if (nanosTimeout <= 0L) {
+                    timedout = transferAfterCancelledWait(node);
+                    break;
+                }
+                if (nanosTimeout >= spinForTimeoutThreshold)
+                    LockSupport.parkNanos(nanosTimeout);
+                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+                    break;
+                long now = System.nanoTime();
+                nanosTimeout -= now - lastTime;
+                lastTime = now;
+            }
+            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+                interruptMode = REINTERRUPT;
+            if (node.nextWaiter != null)
+                unlinkCancelledWaiters();
+            if (interruptMode != 0)
+                reportInterruptAfterWait(interruptMode);
+            return !timedout;
+        }
+
+        //  support for instrumentation
+
+        /**
+         * Returns true if this condition was created by the given
+         * synchronization object.
+         *
+         * @return {@code true} if owned
+         */
+        final boolean isOwnedBy(AbstractQueuedLongSynchronizer sync) {
+            return sync == AbstractQueuedLongSynchronizer.this;
+        }
+
+        /**
+         * Queries whether any threads are waiting on this condition.
+         * Implements {@link AbstractQueuedLongSynchronizer#hasWaiters}.
+         *
+         * @return {@code true} if there are any waiting threads
+         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+         *         returns {@code false}
+         */
+        protected final boolean hasWaiters() {
+            if (!isHeldExclusively())
+                throw new IllegalMonitorStateException();
+            for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+                if (w.waitStatus == Node.CONDITION)
+                    return true;
+            }
+            return false;
+        }
+
+        /**
+         * Returns an estimate of the number of threads waiting on
+         * this condition.
+         * Implements {@link AbstractQueuedLongSynchronizer#getWaitQueueLength}.
+         *
+         * @return the estimated number of waiting threads
+         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+         *         returns {@code false}
+         */
+        protected final int getWaitQueueLength() {
+            if (!isHeldExclusively())
+                throw new IllegalMonitorStateException();
+            int n = 0;
+            for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+                if (w.waitStatus == Node.CONDITION)
+                    ++n;
+            }
+            return n;
+        }
+
+        /**
+         * Returns a collection containing those threads that may be
+         * waiting on this Condition.
+         * Implements {@link AbstractQueuedLongSynchronizer#getWaitingThreads}.
+         *
+         * @return the collection of threads
+         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+         *         returns {@code false}
+         */
+        protected final Collection<Thread> getWaitingThreads() {
+            if (!isHeldExclusively())
+                throw new IllegalMonitorStateException();
+            ArrayList<Thread> list = new ArrayList<Thread>();
+            for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+                if (w.waitStatus == Node.CONDITION) {
+                    Thread t = w.thread;
+                    if (t != null)
+                        list.add(t);
+                }
+            }
+            return list;
+        }
+    }
+
+    /**
+     * Setup to support compareAndSet. We need to natively implement
+     * this here: For the sake of permitting future enhancements, we
+     * cannot explicitly subclass AtomicLong, which would be
+     * efficient and useful otherwise. So, as the lesser of evils, we
+     * natively implement using hotspot intrinsics API. And while we
+     * are at it, we do the same for other CASable fields (which could
+     * otherwise be done with atomic field updaters).
+     */
+    private static final Unsafe unsafe = Unsafe.getUnsafe();
+    private static final long stateOffset;
+    private static final long headOffset;
+    private static final long tailOffset;
+    private static final long waitStatusOffset;
+    private static final long nextOffset;
+
+    static {
+        try {
+            stateOffset = unsafe.objectFieldOffset
+                (AbstractQueuedLongSynchronizer.class.getDeclaredField("state"));
+            headOffset = unsafe.objectFieldOffset
+                (AbstractQueuedLongSynchronizer.class.getDeclaredField("head"));
+            tailOffset = unsafe.objectFieldOffset
+                (AbstractQueuedLongSynchronizer.class.getDeclaredField("tail"));
+            waitStatusOffset = unsafe.objectFieldOffset
+                (Node.class.getDeclaredField("waitStatus"));
+            nextOffset = unsafe.objectFieldOffset
+                (Node.class.getDeclaredField("next"));
+
+        } catch (Exception ex) { throw new Error(ex); }
+    }
+
+    /**
+     * CAS head field. Used only by enq.
+     */
+    private final boolean compareAndSetHead(Node update) {
+        return unsafe.compareAndSwapObject(this, headOffset, null, update);
+    }
+
+    /**
+     * CAS tail field. Used only by enq.
+     */
+    private final boolean compareAndSetTail(Node expect, Node update) {
+        return unsafe.compareAndSwapObject(this, tailOffset, expect, update);
+    }
+
+    /**
+     * CAS waitStatus field of a node.
+     */
+    private final static boolean compareAndSetWaitStatus(Node node,
+                                                         int expect,
+                                                         int update) {
+        return unsafe.compareAndSwapInt(node, waitStatusOffset,
+                                        expect, update);
+    }
+
+    /**
+     * CAS next field of a node.
+     */
+    private final static boolean compareAndSetNext(Node node,
+                                                   Node expect,
+                                                   Node update) {
+        return unsafe.compareAndSwapObject(node, nextOffset, expect, update);
+    }
+}

Propchange: harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java
------------------------------------------------------------------------------
    svn:eol-style = native

Modified: harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedSynchronizer.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedSynchronizer.java?rev=800934&r1=800933&r2=800934&view=diff
==============================================================================
--- harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedSynchronizer.java (original)
+++ harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/AbstractQueuedSynchronizer.java Tue Aug  4 19:39:24 2009
@@ -94,6 +94,12 @@
  * means of using this class. All other methods are declared
  * <tt>final</tt> because they cannot be independently varied.
  *
+ * <p>You may also find the inherited methods from {@link
+ * AbstractOwnableSynchronizer} useful to keep track of the thread
+ * owning an exclusive synchronizer.  You are encouraged to use them
+ * -- this enables monitoring and diagnostic tools to assist users in
+ * determining which threads hold locks.
+ *
  * <p>Even though this class is based on an internal FIFO queue, it
  * does not automatically enforce FIFO acquisition policies.  The core
  * of exclusive synchronization takes the form:
@@ -152,7 +158,10 @@
  *
  * <p>Here is a non-reentrant mutual exclusion lock class that uses
  * the value zero to represent the unlocked state, and one to
- * represent the locked state. It also supports conditions and exposes
+ * represent the locked state. While a non-reentrant lock
+ * does not strictly require recording of the current owner
+ * thread, this class does so anyway to make usage easier to monitor.
+ * It also supports conditions and exposes
  * one of the instrumentation methods:
  *
  * <pre>
@@ -168,13 +177,18 @@
  *     // Acquire the lock if state is zero
  *     public boolean tryAcquire(int acquires) {
  *       assert acquires == 1; // Otherwise unused
- *       return compareAndSetState(0, 1);
+ *       if (compareAndSetState(0, 1)) {
+ *         setExclusiveOwnerThread(Thread.currentThread());
+ *         return true;
+ *       }
+ *       return false;
  *     }
  *
  *     // Release the lock by setting state to zero
  *     protected boolean tryRelease(int releases) {
  *       assert releases == 1; // Otherwise unused
  *       if (getState() == 0) throw new IllegalMonitorStateException();
+ *       setExclusiveOwnerThread(null);
  *       setState(0);
  *       return true;
  *     }
@@ -1641,6 +1655,7 @@
      * Transfers node, if necessary, to sync queue after a cancelled
      * wait. Returns true if thread was cancelled before being
      * signalled.
+     * @param current the waiting thread
      * @param node its node
      * @return true if cancelled before the node was signalled
      */

Modified: harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantReadWriteLock.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantReadWriteLock.java?rev=800934&r1=800933&r2=800934&view=diff
==============================================================================
--- harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantReadWriteLock.java (original)
+++ harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantReadWriteLock.java Tue Aug  4 19:39:24 2009
@@ -1161,6 +1161,32 @@
                                        "[Locked by thread " + o.getName() + "]");
         }
 
+        /**
+         * Queries if this write lock is held by the current thread.
+         * Identical in effect to {@link
+         * ReentrantReadWriteLock#isWriteLockedByCurrentThread}.
+         *
+         * @return {@code true} if the current thread holds this lock and
+         *         {@code false} otherwise
+         * @since 1.6
+         */
+        public boolean isHeldByCurrentThread() {
+            return sync.isHeldExclusively();
+        }
+
+        /**
+         * Queries the number of holds on this write lock by the current
+         * thread.  A thread has a hold on a lock for each lock action
+         * that is not matched by an unlock action.  Identical in effect
+         * to {@link ReentrantReadWriteLock#getWriteHoldCount}.
+         *
+         * @return the number of holds on this lock by the current thread,
+         *         or zero if this lock is not held by the current thread
+         * @since 1.6
+         */
+        public int getHoldCount() {
+            return sync.getWriteHoldCount();
+        }
     }
 
     // Instrumentation and status
@@ -1236,6 +1262,19 @@
     }
 
     /**
+     * Queries the number of reentrant read holds on this lock by the
+     * current thread.  A reader thread has a hold on a lock for
+     * each lock action that is not matched by an unlock action.
+     *
+     * @return the number of holds on the read lock by the current thread,
+     *         or zero if the read lock is not held by the current thread
+     * @since 1.6
+     */
+    public int getReadHoldCount() {
+        return sync.getReadHoldCount();
+    }
+
+    /**
      * Returns a collection containing threads that may be waiting to
      * acquire the write lock.  Because the actual set of threads may
      * change dynamically while constructing this result, the returned



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