Do not use ForkJoinPool when running on IBM J9;...

Do not use ForkJoinPool when running on IBM J9; in this case use 1.5
ThreadPoolScheduler.

1 files changed, 959 insertions, 0 deletions

diff --git a/src/actors/scala/actors/threadpool/locks/ReentrantLock.java b/src/actors/scala/actors/threadpool/locks/ReentrantLock.java
new file mode 100644
index 0000000000..b42ddd611b
--- /dev/null
+++ b/src/actors/scala/actors/threadpool/locks/ReentrantLock.java
@@ -0,0 +1,959 @@
+/*
+ * 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 scala.actors.threadpool.locks;
+
+import java.util.Collection;
+import scala.actors.threadpool.*;
+import scala.actors.threadpool.helpers.*;
+
+/**
+ * A reentrant mutual exclusion {@link Lock} with the same basic
+ * behavior and semantics as the implicit monitor lock accessed using
+ * {@code synchronized} methods and statements, but with extended
+ * capabilities.
+ *
+ * <p>A {@code ReentrantLock} is <em>owned</em> by the thread last
+ * successfully locking, but not yet unlocking it. A thread invoking
+ * {@code lock} will return, successfully acquiring the lock, when
+ * the lock is not owned by another thread. The method will return
+ * immediately if the current thread already owns the lock. This can
+ * be checked using methods {@link #isHeldByCurrentThread}, and {@link
+ * #getHoldCount}.
+ *
+ * <p>The constructor for this class accepts an optional
+ * <em>fairness</em> parameter.  When set {@code true}, under
+ * contention, locks favor granting access to the longest-waiting
+ * thread.  Otherwise this lock does not guarantee any particular
+ * access order.  Programs using fair locks accessed by many threads
+ * may display lower overall throughput (i.e., are slower; often much
+ * slower) than those using the default setting, but have smaller
+ * variances in times to obtain locks and guarantee lack of
+ * starvation. Note however, that fairness of locks does not guarantee
+ * fairness of thread scheduling. Thus, one of many threads using a
+ * fair lock may obtain it multiple times in succession while other
+ * active threads are not progressing and not currently holding the
+ * lock.
+ * Also note that the untimed {@link #tryLock() tryLock} method does not
+ * honor the fairness setting. It will succeed if the lock
+ * is available even if other threads are waiting.
+ *
+ * <p>It is recommended practice to <em>always</em> immediately
+ * follow a call to {@code lock} with a {@code try} block, most
+ * typically in a before/after construction such as:
+ *
+ * <pre>
+ * class X {
+ *   private final ReentrantLock lock = new ReentrantLock();
+ *   // ...
+ *
+ *   public void m() {
+ *     lock.lock();  // block until condition holds
+ *     try {
+ *       // ... method body
+ *     } finally {
+ *       lock.unlock()
+ *     }
+ *   }
+ * }
+ * </pre>
+ *
+ * <p>In addition to implementing the {@link Lock} interface, this
+ * class defines methods {@code isLocked} and
+ * {@code getLockQueueLength}, as well as some associated
+ * {@code protected} access methods that may be useful for
+ * instrumentation and monitoring.
+ *
+ * <p>Serialization of this class behaves in the same way as built-in
+ * locks: a deserialized lock is in the unlocked state, regardless of
+ * its state when serialized.
+ *
+ * <p>This lock supports a maximum of 2147483647 recursive locks by
+ * the same thread. Attempts to exceed this limit result in
+ * {@link Error} throws from locking methods.
+ *
+ * @since 1.5
+ * @author Doug Lea
+ * @author Dawid Kurzyniec
+ */
+public class ReentrantLock implements Lock, java.io.Serializable,
+                                      CondVar.ExclusiveLock {
+    private static final long serialVersionUID = 7373984872572414699L;
+
+    private final Sync sync;
+
+    /**
+     * Base of synchronization control for this lock. Subclassed
+     * into fair and nonfair versions below.
+     */
+    static abstract class Sync implements java.io.Serializable {
+        private static final long serialVersionUID = -5179523762034025860L;
+
+        protected transient Thread owner_ = null;
+        protected transient int holds_ = 0;
+
+        protected Sync() {}
+
+        /**
+         * Performs {@link Lock#lock}. The main reason for subclassing
+         * is to allow fast path for nonfair version.
+         */
+        public abstract void lock();
+
+        public abstract void lockInterruptibly() throws InterruptedException;
+
+        final void incHolds() {
+            int nextHolds = ++holds_;
+            if (nextHolds < 0)
+                throw new Error("Maximum lock count exceeded");
+            holds_ = nextHolds;
+        }
+
+        public boolean tryLock() {
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return true;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        public abstract boolean tryLock(long nanos) throws InterruptedException;
+
+        public abstract void unlock();
+
+        public synchronized int getHoldCount() {
+            return isHeldByCurrentThread() ? holds_ : 0;
+        }
+
+        public synchronized boolean isHeldByCurrentThread() {
+            return holds_ > 0 && Thread.currentThread() == owner_;
+        }
+
+        public synchronized boolean isLocked() {
+            return owner_ != null;
+        }
+
+        public abstract boolean isFair();
+
+        protected synchronized Thread getOwner() {
+            return owner_;
+        }
+
+        public boolean hasQueuedThreads() {
+            throw new UnsupportedOperationException("Use FAIR version");
+        }
+
+        public int getQueueLength() {
+            throw new UnsupportedOperationException("Use FAIR version");
+        }
+
+        public Collection getQueuedThreads() {
+            throw new UnsupportedOperationException("Use FAIR version");
+        }
+
+        public boolean isQueued(Thread thread) {
+            throw new UnsupportedOperationException("Use FAIR version");
+        }
+    }
+
+    /**
+     * Sync object for non-fair locks
+     */
+    final static class NonfairSync extends Sync {
+        private static final long serialVersionUID = 7316153563782823691L;
+
+        NonfairSync() {}
+
+        /**
+         * Performs lock.  Try immediate barge, backing up to normal
+         * acquire on failure.
+         */
+        public void lock() {
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return;
+                }
+                else {
+                    boolean wasInterrupted = Thread.interrupted();
+                    try {
+                        while (true) {
+                            try {
+                                wait();
+                            }
+                            catch (InterruptedException e) {
+                                wasInterrupted = true;
+                                // no need to notify; if we were signalled, we
+                                // will act as signalled, ignoring the
+                                // interruption
+                            }
+                            if (owner_ == null) {
+                                owner_ = caller;
+                                holds_ = 1;
+                                return;
+                            }
+                        }
+                    }
+                    finally {
+                        if (wasInterrupted) Thread.currentThread().interrupt();
+                    }
+                }
+            }
+        }
+
+        public void lockInterruptibly() throws InterruptedException {
+            if (Thread.interrupted()) throw new InterruptedException();
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return;
+                }
+                else {
+                    try {
+                        do { wait(); } while (owner_ != null);
+                        owner_ = caller;
+                        holds_ = 1;
+                        return;
+                    }
+                    catch (InterruptedException ex) {
+                        if (owner_ == null) notify();
+                        throw ex;
+                    }
+                }
+            }
+        }
+
+        public boolean tryLock(long nanos) throws InterruptedException {
+            if (Thread.interrupted()) throw new InterruptedException();
+            Thread caller = Thread.currentThread();
+
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return true;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return true;
+                }
+                else if (nanos <= 0)
+                    return false;
+                else {
+                    long deadline = Utils.nanoTime() + nanos;
+                    try {
+                        for (; ; ) {
+                            TimeUnit.NANOSECONDS.timedWait(this, nanos);
+                            if (caller == owner_) {
+                                incHolds();
+                                return true;
+                            }
+                            else if (owner_ == null) {
+                                owner_ = caller;
+                                holds_ = 1;
+                                return true;
+                            }
+                            else {
+                                nanos = deadline - Utils.nanoTime();
+                                if (nanos <= 0)
+                                    return false;
+                            }
+                        }
+                    }
+                    catch (InterruptedException ex) {
+                        if (owner_ == null) notify();
+                        throw ex;
+                    }
+                }
+            }
+        }
+
+        public synchronized void unlock() {
+            if (Thread.currentThread() != owner_)
+                throw new IllegalMonitorStateException("Not owner");
+
+            if (--holds_ == 0) {
+                owner_ = null;
+                notify();
+            }
+        }
+
+        public final boolean isFair() {
+            return false;
+        }
+    }
+
+    /**
+     * Sync object for fair locks
+     */
+    final static class FairSync extends Sync implements WaitQueue.QueuedSync {
+        private static final long serialVersionUID = -3000897897090466540L;
+
+        private transient WaitQueue wq_ = new FIFOWaitQueue();
+
+        FairSync() {}
+
+        public synchronized boolean recheck(WaitQueue.WaitNode node) {
+            Thread caller = Thread.currentThread();
+            if (owner_ == null) {
+                owner_ = caller;
+                holds_ = 1;
+                return true;
+            }
+            else if (caller == owner_) {
+                incHolds();
+                return true;
+            }
+            wq_.insert(node);
+            return false;
+        }
+
+        public synchronized void takeOver(WaitQueue.WaitNode node) {
+            // assert (holds_ == 1 && owner_ == Thread.currentThread()
+            owner_ = node.getOwner();
+        }
+
+        public void lock() {
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return;
+                }
+            }
+            WaitQueue.WaitNode n = new WaitQueue.WaitNode();
+            n.doWaitUninterruptibly(this);
+        }
+
+        public void lockInterruptibly() throws InterruptedException {
+            if (Thread.interrupted()) throw new InterruptedException();
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return;
+                }
+            }
+            WaitQueue.WaitNode n = new WaitQueue.WaitNode();
+            n.doWait(this);
+        }
+
+        public boolean tryLock(long nanos) throws InterruptedException {
+            if (Thread.interrupted()) throw new InterruptedException();
+            Thread caller = Thread.currentThread();
+            synchronized (this) {
+                if (owner_ == null) {
+                    owner_ = caller;
+                    holds_ = 1;
+                    return true;
+                }
+                else if (caller == owner_) {
+                    incHolds();
+                    return true;
+                }
+            }
+            WaitQueue.WaitNode n = new WaitQueue.WaitNode();
+            return n.doTimedWait(this, nanos);
+        }
+
+        protected synchronized WaitQueue.WaitNode getSignallee(Thread caller) {
+            if (caller != owner_)
+                throw new IllegalMonitorStateException("Not owner");
+            // assert (holds_ > 0)
+            if (holds_ >= 2) { // current thread will keep the lock
+                --holds_;
+                return null;
+            }
+            // assert (holds_ == 1)
+            WaitQueue.WaitNode w = wq_.extract();
+            if (w == null) { // if none, clear for new arrivals
+                owner_ = null;
+                holds_ = 0;
+            }
+            return w;
+        }
+
+        public void unlock() {
+            Thread caller = Thread.currentThread();
+            for (;;) {
+                WaitQueue.WaitNode w = getSignallee(caller);
+                if (w == null) return;  // no one to signal
+                if (w.signal(this)) return; // notify if still waiting, else skip
+            }
+        }
+
+        public final boolean isFair() {
+            return true;
+        }
+
+        public synchronized boolean hasQueuedThreads() {
+            return wq_.hasNodes();
+        }
+
+        public synchronized int getQueueLength() {
+            return wq_.getLength();
+        }
+
+        public synchronized Collection getQueuedThreads() {
+            return wq_.getWaitingThreads();
+        }
+
+        public synchronized boolean isQueued(Thread thread) {
+            return wq_.isWaiting(thread);
+        }
+
+        private void readObject(java.io.ObjectInputStream in)
+                throws java.io.IOException, ClassNotFoundException {
+            in.defaultReadObject();
+            synchronized (this) {
+                wq_ = new FIFOWaitQueue();
+            }
+        }
+    }
+
+    /**
+     * Creates an instance of {@code ReentrantLock}.
+     * This is equivalent to using {@code ReentrantLock(false)}.
+     */
+    public ReentrantLock() {
+        sync = new NonfairSync();
+    }
+
+    /**
+     * Creates an instance of {@code ReentrantLock} with the
+     * given fairness policy.
+     *
+     * @param fair {@code true} if this lock should use a fair ordering policy
+     */
+    public ReentrantLock(boolean fair) {
+        sync = (fair)? (Sync)new FairSync() : new NonfairSync();
+    }
+
+
+    /**
+     * Acquires the lock.
+     *
+     * <p>Acquires the lock if it is not held by another thread and returns
+     * immediately, setting the lock hold count to one.
+     *
+     * <p>If the current thread already holds the lock then the hold
+     * count is incremented by one and the method returns immediately.
+     *
+     * <p>If the lock is held by another thread then the
+     * current thread becomes disabled for thread scheduling
+     * purposes and lies dormant until the lock has been acquired,
+     * at which time the lock hold count is set to one.
+     */
+    public void lock() {
+        sync.lock();
+    }
+
+    /**
+     * Acquires the lock unless the current thread is
+     * {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires the lock if it is not held by another thread and returns
+     * immediately, setting the lock hold count to one.
+     *
+     * <p>If the current thread already holds this lock then the hold count
+     * is incremented by one and the method returns immediately.
+     *
+     * <p>If the lock is held by another thread then the
+     * current thread becomes disabled for thread scheduling
+     * purposes and lies dormant until one of two things happens:
+     *
+     * <ul>
+     *
+     * <li>The lock is acquired by the current thread; or
+     *
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
+     * current thread.
+     *
+     * </ul>
+     *
+     * <p>If the lock is acquired by the current thread then the lock hold
+     * count is set to one.
+     *
+     * <p>If the current thread:
+     *
+     * <ul>
+     *
+     * <li>has its interrupted status set on entry to this method; or
+     *
+     * <li>is {@linkplain Thread#interrupt interrupted} while acquiring
+     * the lock,
+     *
+     * </ul>
+     *
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     *
+     * <p>In this implementation, as this method is an explicit
+     * interruption point, preference is given to responding to the
+     * interrupt over normal or reentrant acquisition of the lock.
+     *
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public void lockInterruptibly() throws InterruptedException {
+        sync.lockInterruptibly();
+    }
+
+    /**
+     * Acquires the lock only if it is not held by another thread at the time
+     * of invocation.
+     *
+     * <p>Acquires the lock if it is not held by another thread and
+     * returns immediately with the value {@code true}, setting the
+     * lock hold count to one. Even when this lock has been set to use a
+     * fair ordering policy, a call to {@code tryLock()} <em>will</em>
+     * immediately acquire the lock if it is available, whether or not
+     * other threads are currently waiting for the lock.
+     * This &quot;barging&quot; behavior can be useful in certain
+     * circumstances, even though it breaks fairness. If you want to honor
+     * the fairness setting for this lock, then use
+     * {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
+     * which is almost equivalent (it also detects interruption).
+     *
+     * <p> If the current thread already holds this lock then the hold
+     * count is incremented by one and the method returns {@code true}.
+     *
+     * <p>If the lock is held by another thread then this method will return
+     * immediately with the value {@code false}.
+     *
+     * @return {@code true} if the lock was free and was acquired by the
+     *         current thread, or the lock was already held by the current
+     *         thread; and {@code false} otherwise
+     */
+    public boolean tryLock() {
+        return sync.tryLock();
+    }
+
+    /**
+     * Acquires the lock if it is not held by another thread within the given
+     * waiting time and the current thread has not been
+     * {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires the lock if it is not held by another thread and returns
+     * immediately with the value {@code true}, setting the lock hold count
+     * to one. If this lock has been set to use a fair ordering policy then
+     * an available lock <em>will not</em> be acquired if any other threads
+     * are waiting for the lock. This is in contrast to the {@link #tryLock()}
+     * method. If you want a timed {@code tryLock} that does permit barging on
+     * a fair lock then combine the timed and un-timed forms together:
+     *
+     * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
+     * </pre>
+     *
+     * <p>If the current thread
+     * already holds this lock then the hold count is incremented by one and
+     * the method returns {@code true}.
+     *
+     * <p>If the lock is held by another thread then the
+     * current thread becomes disabled for thread scheduling
+     * purposes and lies dormant until one of three things happens:
+     *
+     * <ul>
+     *
+     * <li>The lock is acquired by the current thread; or
+     *
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread; or
+     *
+     * <li>The specified waiting time elapses
+     *
+     * </ul>
+     *
+     * <p>If the lock is acquired then the value {@code true} is returned and
+     * the lock hold count is set to one.
+     *
+     * <p>If the current thread:
+     *
+     * <ul>
+     *
+     * <li>has its interrupted status set on entry to this method; or
+     *
+     * <li>is {@linkplain Thread#interrupt interrupted} while
+     * acquiring the lock,
+     *
+     * </ul>
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     *
+     * <p>If the specified waiting time elapses then the value {@code false}
+     * is returned.  If the time is less than or equal to zero, the method
+     * will not wait at all.
+     *
+     * <p>In this implementation, as this method is an explicit
+     * interruption point, preference is given to responding to the
+     * interrupt over normal or reentrant acquisition of the lock, and
+     * over reporting the elapse of the waiting time.
+     *
+     * @param timeout the time to wait for the lock
+     * @param unit the time unit of the timeout argument
+     * @return {@code true} if the lock was free and was acquired by the
+     *         current thread, or the lock was already held by the current
+     *         thread; and {@code false} if the waiting time elapsed before
+     *         the lock could be acquired
+     * @throws InterruptedException if the current thread is interrupted
+     * @throws NullPointerException if the time unit is null
+     *
+     */
+    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
+        return sync.tryLock(unit.toNanos(timeout));
+    }
+
+    /**
+     * Attempts to release this lock.
+     *
+     * <p>If the current thread is the holder of this lock then the hold
+     * count is decremented.  If the hold count is now zero then the lock
+     * is released.  If the current thread is not the holder of this
+     * lock then {@link IllegalMonitorStateException} is thrown.
+     *
+     * @throws IllegalMonitorStateException if the current thread does not
+     *         hold this lock
+     */
+    public void unlock() {
+        sync.unlock();
+    }
+
+    /**
+     * Returns a {@link Condition} instance for use with this
+     * {@link Lock} instance.
+     *
+     * <p>The returned {@link Condition} instance supports the same
+     * usages as do the {@link Object} monitor methods ({@link
+     * Object#wait() wait}, {@link Object#notify notify}, and {@link
+     * Object#notifyAll notifyAll}) when used with the built-in
+     * monitor lock.
+     *
+     * <ul>
+     *
+     * <li>If this lock is not held when any of the {@link Condition}
+     * {@linkplain Condition#await() waiting} or {@linkplain
+     * Condition#signal signalling} methods are called, then an {@link
+     * IllegalMonitorStateException} is thrown.
+     *
+     * <li>When the condition {@linkplain Condition#await() waiting}
+     * methods are called the lock is released and, before they
+     * return, the lock is reacquired and the lock hold count restored
+     * to what it was when the method was called.
+     *
+     * <li>If a thread is {@linkplain Thread#interrupt interrupted}
+     * while waiting then the wait will terminate, an {@link
+     * InterruptedException} will be thrown, and the thread's
+     * interrupted status will be cleared.
+     *
+     * <li> Waiting threads are signalled in FIFO order.
+     *
+     * <li>The ordering of lock reacquisition for threads returning
+     * from waiting methods is the same as for threads initially
+     * acquiring the lock, which is in the default case not specified,
+     * but for <em>fair</em> locks favors those threads that have been
+     * waiting the longest.
+     *
+     * </ul>
+     *
+     * @return the Condition object
+     */
+    public Condition newCondition() {
+        return isFair() ? (Condition)new FIFOCondVar(this) : new CondVar(this);
+    }
+
+    /**
+     * Queries the number of holds on this lock by the current thread.
+     *
+     * <p>A thread has a hold on a lock for each lock action that is not
+     * matched by an unlock action.
+     *
+     * <p>The hold count information is typically only used for testing and
+     * debugging purposes. For example, if a certain section of code should
+     * not be entered with the lock already held then we can assert that
+     * fact:
+     *
+     * <pre>
+     * class X {
+     *   ReentrantLock lock = new ReentrantLock();
+     *   // ...
+     *   public void m() {
+     *     assert lock.getHoldCount() == 0;
+     *     lock.lock();
+     *     try {
+     *       // ... method body
+     *     } finally {
+     *       lock.unlock();
+     *     }
+     *   }
+     * }
+     * </pre>
+     *
+     * @return the number of holds on this lock by the current thread,
+     *         or zero if this lock is not held by the current thread
+     */
+    public int getHoldCount() {
+        return sync.getHoldCount();
+    }
+
+    /**
+     * Queries if this lock is held by the current thread.
+     *
+     * <p>Analogous to the {@link Thread#holdsLock} method for built-in
+     * monitor locks, this method is typically used for debugging and
+     * testing. For example, a method that should only be called while
+     * a lock is held can assert that this is the case:
+     *
+     * <pre>
+     * class X {
+     *   ReentrantLock lock = new ReentrantLock();
+     *   // ...
+     *
+     *   public void m() {
+     *       assert lock.isHeldByCurrentThread();
+     *       // ... method body
+     *   }
+     * }
+     * </pre>
+     *
+     * <p>It can also be used to ensure that a reentrant lock is used
+     * in a non-reentrant manner, for example:
+     *
+     * <pre>
+     * class X {
+     *   ReentrantLock lock = new ReentrantLock();
+     *   // ...
+     *
+     *   public void m() {
+     *       assert !lock.isHeldByCurrentThread();
+     *       lock.lock();
+     *       try {
+     *           // ... method body
+     *       } finally {
+     *           lock.unlock();
+     *       }
+     *   }
+     * }
+     * </pre>
+     *
+     * @return {@code true} if current thread holds this lock and
+     *         {@code false} otherwise
+     */
+    public boolean isHeldByCurrentThread() {
+        return sync.isHeldByCurrentThread();
+    }
+
+    /**
+     * Queries if this lock is held by any thread. This method is
+     * designed for use in monitoring of the system state,
+     * not for synchronization control.
+     *
+     * @return {@code true} if any thread holds this lock and
+     *         {@code false} otherwise
+     */
+    public boolean isLocked() {
+        return sync.isLocked();
+    }
+
+    /**
+     * Returns {@code true} if this lock has fairness set true.
+     *
+     * @return {@code true} if this lock has fairness set true
+     */
+    public final boolean isFair() {
+        return sync.isFair();
+    }
+
+    /**
+     * Returns the thread that currently owns this lock, or
+     * {@code null} if not owned. When this method is called by a
+     * thread that is not the owner, the return value reflects a
+     * best-effort approximation of current lock status. For example,
+     * the owner may be momentarily {@code null} even if there are
+     * threads trying to acquire the lock but have not yet done so.
+     * This method is designed to facilitate construction of
+     * subclasses that provide more extensive lock monitoring
+     * facilities.
+     *
+     * @return the owner, or {@code null} if not owned
+     */
+    protected Thread getOwner() {
+        return sync.getOwner();
+    }
+
+    /**
+     * Queries whether any threads are waiting to acquire this lock. Note that
+     * because cancellations may occur at any time, a {@code true}
+     * return does not guarantee that any other thread will ever
+     * acquire this lock.  This method is designed primarily for use in
+     * monitoring of the system state.
+     *
+     * @return {@code true} if there may be other threads waiting to
+     *         acquire the lock
+     */
+    public final boolean hasQueuedThreads() {
+        return sync.hasQueuedThreads();
+    }
+
+
+    /**
+     * Queries whether the given thread is waiting to acquire this
+     * lock. Note that because cancellations may occur at any time, a
+     * {@code true} return does not guarantee that this thread
+     * will ever acquire this lock.  This method is designed primarily for use
+     * in monitoring of the system state.
+     *
+     * @param thread the thread
+     * @return {@code true} if the given thread is queued waiting for this lock
+     * @throws NullPointerException if the thread is null
+     */
+    public final boolean hasQueuedThread(Thread thread) {
+        return sync.isQueued(thread);
+    }
+
+
+    /**
+     * Returns an estimate of the number of threads waiting to
+     * acquire this lock.  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 of the system state, not for synchronization
+     * control.
+     *
+     * @return the estimated number of threads waiting for this lock
+     */
+    public final int getQueueLength() {
+        return sync.getQueueLength();
+    }
+
+    /**
+     * Returns a collection containing threads that may be waiting to
+     * acquire this lock.  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
+     */
+    protected Collection getQueuedThreads() {
+        return sync.getQueuedThreads();
+    }
+
+    /**
+     * Queries whether any threads are waiting on the given condition
+     * associated with this lock. Note that because timeouts and
+     * interrupts may occur at any time, a {@code true} return does
+     * not guarantee that a future {@code signal} will awaken any
+     * threads.  This method is designed primarily for use in
+     * monitoring of the system state.
+     *
+     * @param condition the condition
+     * @return {@code true} if there are any waiting threads
+     * @throws IllegalMonitorStateException if this lock is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
+     */
+    public boolean hasWaiters(Condition condition) {
+        return asCondVar(condition).hasWaiters();
+    }
+
+    /**
+     * Returns an estimate of the number of threads waiting on the
+     * given condition associated with this lock. 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 this lock is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
+     */
+    public int getWaitQueueLength(Condition condition) {
+        return asCondVar(condition).getWaitQueueLength();
+    }
+
+    /**
+     * Returns a collection containing those threads that may be
+     * waiting on the given condition associated with this lock.
+     * 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 condition monitoring facilities.
+     *
+     * @param condition the condition
+     * @return the collection of threads
+     * @throws IllegalMonitorStateException if this lock is not held
+     * @throws IllegalArgumentException if the given condition is
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
+     */
+    protected Collection getWaitingThreads(Condition condition) {
+        return asCondVar(condition).getWaitingThreads();
+    }
+
+    /**
+     * Returns a string identifying this lock, as well as its lock state.
+     * The state, in brackets, includes either the String {@code "Unlocked"}
+     * or the String {@code "Locked by"} followed by the
+     * {@linkplain Thread#getName name} of the owning thread.
+     *
+     * @return a string identifying this lock, as well as its lock state
+     */
+    public String toString() {
+        Thread o = getOwner();
+        return super.toString() + ((o == null) ?
+                                   "[Unlocked]" :
+                                   "[Locked by thread " + o.getName() + "]");
+    }
+
+    private CondVar asCondVar(Condition condition) {
+        if (condition == null)
+            throw new NullPointerException();
+        if (!(condition instanceof CondVar))
+            throw new IllegalArgumentException("not owner");
+        CondVar condVar = (CondVar)condition;
+        if (condVar.lock != this)
+            throw new IllegalArgumentException("not owner");
+        return condVar;
+    }
+}