--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/locks/ReentrantLock.java Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,769 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * 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.*;
+
+/**
+ * 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
+ */
+public class ReentrantLock implements Lock, java.io.Serializable {
+ private static final long serialVersionUID = 7373984872572414699L;
+ /** Synchronizer providing all implementation mechanics */
+ private final Sync sync;
+
+ /**
+ * Base of synchronization control for this lock. Subclassed
+ * into fair and nonfair versions below. Uses AQS state to
+ * represent the number of holds on the lock.
+ */
+ static abstract class Sync extends AbstractQueuedSynchronizer {
+ private static final long serialVersionUID = -5179523762034025860L;
+
+ /**
+ * Performs {@link Lock#lock}. The main reason for subclassing
+ * is to allow fast path for nonfair version.
+ */
+ abstract void lock();
+
+ /**
+ * Performs non-fair tryLock. tryAcquire is
+ * implemented in subclasses, but both need nonfair
+ * try for trylock method.
+ */
+ final boolean nonfairTryAcquire(int acquires) {
+ final Thread current = Thread.currentThread();
+ int c = getState();
+ if (c == 0) {
+ if (compareAndSetState(0, acquires)) {
+ setExclusiveOwnerThread(current);
+ return true;
+ }
+ }
+ else if (current == getExclusiveOwnerThread()) {
+ int nextc = c + acquires;
+ if (nextc < 0) // overflow
+ throw new Error("Maximum lock count exceeded");
+ setState(nextc);
+ return true;
+ }
+ return false;
+ }
+
+ protected final boolean tryRelease(int releases) {
+ int c = getState() - releases;
+ if (Thread.currentThread() != getExclusiveOwnerThread())
+ throw new IllegalMonitorStateException();
+ boolean free = false;
+ if (c == 0) {
+ free = true;
+ setExclusiveOwnerThread(null);
+ }
+ setState(c);
+ return free;
+ }
+
+ protected final boolean isHeldExclusively() {
+ // While we must in general read state before owner,
+ // we don't need to do so to check if current thread is owner
+ return getExclusiveOwnerThread() == Thread.currentThread();
+ }
+
+ final ConditionObject newCondition() {
+ return new ConditionObject();
+ }
+
+ // Methods relayed from outer class
+
+ final Thread getOwner() {
+ return getState() == 0 ? null : getExclusiveOwnerThread();
+ }
+
+ final int getHoldCount() {
+ return isHeldExclusively() ? getState() : 0;
+ }
+
+ final boolean isLocked() {
+ return getState() != 0;
+ }
+
+ /**
+ * Reconstitutes this lock instance from a stream.
+ * @param s the stream
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+ setState(0); // reset to unlocked state
+ }
+ }
+
+ /**
+ * Sync object for non-fair locks
+ */
+ final static class NonfairSync extends Sync {
+ private static final long serialVersionUID = 7316153563782823691L;
+
+ /**
+ * Performs lock. Try immediate barge, backing up to normal
+ * acquire on failure.
+ */
+ final void lock() {
+ if (compareAndSetState(0, 1))
+ setExclusiveOwnerThread(Thread.currentThread());
+ else
+ acquire(1);
+ }
+
+ protected final boolean tryAcquire(int acquires) {
+ return nonfairTryAcquire(acquires);
+ }
+ }
+
+ /**
+ * Sync object for fair locks
+ */
+ final static class FairSync extends Sync {
+ private static final long serialVersionUID = -3000897897090466540L;
+
+ final void lock() {
+ acquire(1);
+ }
+
+ /**
+ * Fair version of tryAcquire. Don't grant access unless
+ * recursive call or no waiters or is first.
+ */
+ protected final boolean tryAcquire(int acquires) {
+ final Thread current = Thread.currentThread();
+ int c = getState();
+ if (c == 0) {
+ if (!hasQueuedPredecessors() &&
+ compareAndSetState(0, acquires)) {
+ setExclusiveOwnerThread(current);
+ return true;
+ }
+ }
+ else if (current == getExclusiveOwnerThread()) {
+ int nextc = c + acquires;
+ if (nextc < 0)
+ throw new Error("Maximum lock count exceeded");
+ setState(nextc);
+ return true;
+ }
+ return false;
+ }
+ }
+
+ /**
+ * 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)? 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.acquireInterruptibly(1);
+ }
+
+ /**
+ * 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 "barging" 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.nonfairTryAcquire(1);
+ }
+
+ /**
+ * 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.tryAcquireNanos(1, 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.release(1);
+ }
+
+ /**
+ * 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 sync.newCondition();
+ }
+
+ /**
+ * 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.isHeldExclusively();
+ }
+
+ /**
+ * 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 instanceof FairSync;
+ }
+
+ /**
+ * 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<Thread> 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) {
+ if (condition == null)
+ throw new NullPointerException();
+ if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
+ throw new IllegalArgumentException("not owner");
+ return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
+ }
+
+ /**
+ * 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) {
+ if (condition == null)
+ throw new NullPointerException();
+ if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
+ throw new IllegalArgumentException("not owner");
+ return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
+ }
+
+ /**
+ * 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<Thread> getWaitingThreads(Condition condition) {
+ if (condition == null)
+ throw new NullPointerException();
+ if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
+ throw new IllegalArgumentException("not owner");
+ return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
+ }
+
+ /**
+ * 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 = sync.getOwner();
+ return super.toString() + ((o == null) ?
+ "[Unlocked]" :
+ "[Locked by thread " + o.getName() + "]");
+ }
+}