1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36 package java.util.concurrent.locks;
37
38 import java.util.Collection;
39 import java.util.concurrent.TimeUnit;
40
41 /**
42 * A reentrant mutual exclusion {@link Lock} with the same basic
43 * behavior and semantics as the implicit monitor lock accessed using
44 * {@code synchronized} methods and statements, but with extended
45 * capabilities.
46 *
47 * <p>A {@code ReentrantLock} is <em>owned</em> by the thread last
48 * successfully locking, but not yet unlocking it. A thread invoking
49 * {@code lock} will return, successfully acquiring the lock, when
50 * the lock is not owned by another thread. The method will return
51 * immediately if the current thread already owns the lock. This can
52 * be checked using methods {@link #isHeldByCurrentThread}, and {@link
53 * #getHoldCount}.
54 *
55 * <p>The constructor for this class accepts an optional
56 * <em>fairness</em> parameter. When set {@code true}, under
57 * contention, locks favor granting access to the longest-waiting
58 * thread. Otherwise this lock does not guarantee any particular
59 * access order. Programs using fair locks accessed by many threads
60 * may display lower overall throughput (i.e., are slower; often much
61 * slower) than those using the default setting, but have smaller
62 * variances in times to obtain locks and guarantee lack of
63 * starvation. Note however, that fairness of locks does not guarantee
64 * fairness of thread scheduling. Thus, one of many threads using a
65 * fair lock may obtain it multiple times in succession while other
66 * active threads are not progressing and not currently holding the
67 * lock.
68 * Also note that the untimed {@link #tryLock()} method does not
69 * honor the fairness setting. It will succeed if the lock
70 * is available even if other threads are waiting.
71 *
72 * <p>It is recommended practice to <em>always</em> immediately
73 * follow a call to {@code lock} with a {@code try} block, most
74 * typically in a before/after construction such as:
75 *
76 * <pre> {@code
77 * class X {
78 * private final ReentrantLock lock = new ReentrantLock();
79 * // ...
80 *
81 * public void m() {
82 * lock.lock(); // block until condition holds
83 * try {
84 * // ... method body
85 * } finally {
86 * lock.unlock()
87 * }
88 * }
89 * }}</pre>
90 *
91 * <p>In addition to implementing the {@link Lock} interface, this
92 * class defines a number of {@code public} and {@code protected}
93 * methods for inspecting the state of the lock. Some of these
94 * methods are only useful for instrumentation and monitoring.
95 *
96 * <p>Serialization of this class behaves in the same way as built-in
97 * locks: a deserialized lock is in the unlocked state, regardless of
98 * its state when serialized.
99 *
100 * <p>This lock supports a maximum of 2147483647 recursive locks by
101 * the same thread. Attempts to exceed this limit result in
102 * {@link Error} throws from locking methods.
103 *
104 * @since 1.5
105 * @author Doug Lea
106 */
107 public class ReentrantLock implements Lock, java.io.Serializable {
108 private static final long serialVersionUID = 7373984872572414699L;
109 /** Synchronizer providing all implementation mechanics */
110 private final Sync sync;
111
112 /**
113 * Base of synchronization control for this lock. Subclassed
114 * into fair and nonfair versions below. Uses AQS state to
115 * represent the number of holds on the lock.
116 */
117 abstract static class Sync extends AbstractQueuedSynchronizer {
118 private static final long serialVersionUID = -5179523762034025860L;
119
120 /**
121 * Performs {@link Lock#lock}. The main reason for subclassing
122 * is to allow fast path for nonfair version.
123 */
124 abstract void lock();
125
126 /**
127 * Performs non-fair tryLock. tryAcquire is implemented in
128 * subclasses, but both need nonfair try for trylock method.
129 */
130 final boolean nonfairTryAcquire(int acquires) {
131 final Thread current = Thread.currentThread();
132 int c = getState();
133 if (c == 0) {
134 if (compareAndSetState(0, acquires)) {
135 setExclusiveOwnerThread(current);
136 return true;
137 }
138 }
139 else if (current == getExclusiveOwnerThread()) {
140 int nextc = c + acquires;
141 if (nextc < 0) // overflow
142 throw new Error("Maximum lock count exceeded");
143 setState(nextc);
144 return true;
145 }
146 return false;
147 }
148
149 protected final boolean tryRelease(int releases) {
150 int c = getState() - releases;
151 if (Thread.currentThread() != getExclusiveOwnerThread())
152 throw new IllegalMonitorStateException();
153 boolean free = false;
154 if (c == 0) {
155 free = true;
156 setExclusiveOwnerThread(null);
157 }
158 setState(c);
159 return free;
160 }
161
162 protected final boolean isHeldExclusively() {
163 // While we must in general read state before owner,
164 // we don't need to do so to check if current thread is owner
165 return getExclusiveOwnerThread() == Thread.currentThread();
166 }
167
168 final ConditionObject newCondition() {
169 return new ConditionObject();
170 }
171
172 // Methods relayed from outer class
173
174 final Thread getOwner() {
175 return getState() == 0 ? null : getExclusiveOwnerThread();
176 }
177
178 final int getHoldCount() {
179 return isHeldExclusively() ? getState() : 0;
180 }
181
182 final boolean isLocked() {
183 return getState() != 0;
184 }
185
186 /**
187 * Reconstitutes the instance from a stream (that is, deserializes it).
188 */
189 private void readObject(java.io.ObjectInputStream s)
190 throws java.io.IOException, ClassNotFoundException {
191 s.defaultReadObject();
192 setState(0); // reset to unlocked state
193 }
194 }
195
196 /**
197 * Sync object for non-fair locks
198 */
199 static final class NonfairSync extends Sync {
200 private static final long serialVersionUID = 7316153563782823691L;
201
202 /**
203 * Performs lock. Try immediate barge, backing up to normal
204 * acquire on failure.
205 */
206 final void lock() {
207 if (compareAndSetState(0, 1))
208 setExclusiveOwnerThread(Thread.currentThread());
209 else
210 acquire(1);
211 }
212
213 protected final boolean tryAcquire(int acquires) {
214 return nonfairTryAcquire(acquires);
215 }
216 }
217
218 /**
219 * Sync object for fair locks
220 */
221 static final class FairSync extends Sync {
222 private static final long serialVersionUID = -3000897897090466540L;
223
224 final void lock() {
225 acquire(1);
226 }
227
228 /**
229 * Fair version of tryAcquire. Don't grant access unless
230 * recursive call or no waiters or is first.
231 */
232 protected final boolean tryAcquire(int acquires) {
233 final Thread current = Thread.currentThread();
234 int c = getState();
235 if (c == 0) {
236 if (!hasQueuedPredecessors() &&
237 compareAndSetState(0, acquires)) {
238 setExclusiveOwnerThread(current);
239 return true;
240 }
241 }
242 else if (current == getExclusiveOwnerThread()) {
243 int nextc = c + acquires;
244 if (nextc < 0)
245 throw new Error("Maximum lock count exceeded");
246 setState(nextc);
247 return true;
248 }
249 return false;
250 }
251 }
252
253 /**
254 * Creates an instance of {@code ReentrantLock}.
255 * This is equivalent to using {@code ReentrantLock(false)}.
256 */
257 public ReentrantLock() {
258 sync = new NonfairSync();
259 }
260
261 /**
262 * Creates an instance of {@code ReentrantLock} with the
263 * given fairness policy.
264 *
265 * @param fair {@code true} if this lock should use a fair ordering policy
266 */
267 public ReentrantLock(boolean fair) {
268 sync = fair ? new FairSync() : new NonfairSync();
269 }
270
271 /**
272 * Acquires the lock.
273 *
274 * <p>Acquires the lock if it is not held by another thread and returns
275 * immediately, setting the lock hold count to one.
276 *
277 * <p>If the current thread already holds the lock then the hold
278 * count is incremented by one and the method returns immediately.
279 *
280 * <p>If the lock is held by another thread then the
281 * current thread becomes disabled for thread scheduling
282 * purposes and lies dormant until the lock has been acquired,
283 * at which time the lock hold count is set to one.
284 */
285 public void lock() {
286 sync.lock();
287 }
288
289 /**
290 * Acquires the lock unless the current thread is
291 * {@linkplain Thread#interrupt interrupted}.
292 *
293 * <p>Acquires the lock if it is not held by another thread and returns
294 * immediately, setting the lock hold count to one.
295 *
296 * <p>If the current thread already holds this lock then the hold count
297 * is incremented by one and the method returns immediately.
298 *
299 * <p>If the lock is held by another thread then the
300 * current thread becomes disabled for thread scheduling
301 * purposes and lies dormant until one of two things happens:
302 *
303 * <ul>
304 *
305 * <li>The lock is acquired by the current thread; or
306 *
307 * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
308 * current thread.
309 *
310 * </ul>
311 *
312 * <p>If the lock is acquired by the current thread then the lock hold
313 * count is set to one.
314 *
315 * <p>If the current thread:
316 *
317 * <ul>
318 *
319 * <li>has its interrupted status set on entry to this method; or
320 *
321 * <li>is {@linkplain Thread#interrupt interrupted} while acquiring
322 * the lock,
323 *
324 * </ul>
325 *
326 * then {@link InterruptedException} is thrown and the current thread's
327 * interrupted status is cleared.
328 *
329 * <p>In this implementation, as this method is an explicit
330 * interruption point, preference is given to responding to the
331 * interrupt over normal or reentrant acquisition of the lock.
332 *
333 * @throws InterruptedException if the current thread is interrupted
334 */
335 public void lockInterruptibly() throws InterruptedException {
336 sync.acquireInterruptibly(1);
337 }
338
339 /**
340 * Acquires the lock only if it is not held by another thread at the time
341 * of invocation.
342 *
343 * <p>Acquires the lock if it is not held by another thread and
344 * returns immediately with the value {@code true}, setting the
345 * lock hold count to one. Even when this lock has been set to use a
346 * fair ordering policy, a call to {@code tryLock()} <em>will</em>
347 * immediately acquire the lock if it is available, whether or not
348 * other threads are currently waiting for the lock.
349 * This "barging" behavior can be useful in certain
350 * circumstances, even though it breaks fairness. If you want to honor
351 * the fairness setting for this lock, then use
352 * {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
353 * which is almost equivalent (it also detects interruption).
354 *
355 * <p>If the current thread already holds this lock then the hold
356 * count is incremented by one and the method returns {@code true}.
357 *
358 * <p>If the lock is held by another thread then this method will return
359 * immediately with the value {@code false}.
360 *
361 * @return {@code true} if the lock was free and was acquired by the
362 * current thread, or the lock was already held by the current
363 * thread; and {@code false} otherwise
364 */
365 public boolean tryLock() {
366 return sync.nonfairTryAcquire(1);
367 }
368
369 /**
370 * Acquires the lock if it is not held by another thread within the given
371 * waiting time and the current thread has not been
372 * {@linkplain Thread#interrupt interrupted}.
373 *
374 * <p>Acquires the lock if it is not held by another thread and returns
375 * immediately with the value {@code true}, setting the lock hold count
376 * to one. If this lock has been set to use a fair ordering policy then
377 * an available lock <em>will not</em> be acquired if any other threads
378 * are waiting for the lock. This is in contrast to the {@link #tryLock()}
379 * method. If you want a timed {@code tryLock} that does permit barging on
380 * a fair lock then combine the timed and un-timed forms together:
381 *
382 * <pre> {@code
383 * if (lock.tryLock() ||
384 * lock.tryLock(timeout, unit)) {
385 * ...
386 * }}</pre>
387 *
388 * <p>If the current thread
389 * already holds this lock then the hold count is incremented by one and
390 * the method returns {@code true}.
391 *
392 * <p>If the lock is held by another thread then the
393 * current thread becomes disabled for thread scheduling
394 * purposes and lies dormant until one of three things happens:
395 *
396 * <ul>
397 *
398 * <li>The lock is acquired by the current thread; or
399 *
400 * <li>Some other thread {@linkplain Thread#interrupt interrupts}
401 * the current thread; or
402 *
403 * <li>The specified waiting time elapses
404 *
405 * </ul>
406 *
407 * <p>If the lock is acquired then the value {@code true} is returned and
408 * the lock hold count is set to one.
409 *
410 * <p>If the current thread:
411 *
412 * <ul>
413 *
414 * <li>has its interrupted status set on entry to this method; or
415 *
416 * <li>is {@linkplain Thread#interrupt interrupted} while
417 * acquiring the lock,
418 *
419 * </ul>
420 * then {@link InterruptedException} is thrown and the current thread's
421 * interrupted status is cleared.
422 *
423 * <p>If the specified waiting time elapses then the value {@code false}
424 * is returned. If the time is less than or equal to zero, the method
425 * will not wait at all.
426 *
427 * <p>In this implementation, as this method is an explicit
428 * interruption point, preference is given to responding to the
429 * interrupt over normal or reentrant acquisition of the lock, and
430 * over reporting the elapse of the waiting time.
431 *
432 * @param timeout the time to wait for the lock
433 * @param unit the time unit of the timeout argument
434 * @return {@code true} if the lock was free and was acquired by the
435 * current thread, or the lock was already held by the current
436 * thread; and {@code false} if the waiting time elapsed before
437 * the lock could be acquired
438 * @throws InterruptedException if the current thread is interrupted
439 * @throws NullPointerException if the time unit is null
440 */
441 public boolean tryLock(long timeout, TimeUnit unit)
442 throws InterruptedException {
443 return sync.tryAcquireNanos(1, unit.toNanos(timeout));
444 }
445
446 /**
447 * Attempts to release this lock.
448 *
449 * <p>If the current thread is the holder of this lock then the hold
450 * count is decremented. If the hold count is now zero then the lock
451 * is released. If the current thread is not the holder of this
452 * lock then {@link IllegalMonitorStateException} is thrown.
453 *
454 * @throws IllegalMonitorStateException if the current thread does not
455 * hold this lock
456 */
457 public void unlock() {
458 sync.release(1);
459 }
460
461 /**
462 * Returns a {@link Condition} instance for use with this
463 * {@link Lock} instance.
464 *
465 * <p>The returned {@link Condition} instance supports the same
466 * usages as do the {@link Object} monitor methods ({@link
467 * Object#wait() wait}, {@link Object#notify notify}, and {@link
468 * Object#notifyAll notifyAll}) when used with the built-in
469 * monitor lock.
470 *
471 * <ul>
472 *
473 * <li>If this lock is not held when any of the {@link Condition}
474 * {@linkplain Condition#await() waiting} or {@linkplain
475 * Condition#signal signalling} methods are called, then an {@link
476 * IllegalMonitorStateException} is thrown.
477 *
478 * <li>When the condition {@linkplain Condition#await() waiting}
479 * methods are called the lock is released and, before they
480 * return, the lock is reacquired and the lock hold count restored
481 * to what it was when the method was called.
482 *
483 * <li>If a thread is {@linkplain Thread#interrupt interrupted}
484 * while waiting then the wait will terminate, an {@link
485 * InterruptedException} will be thrown, and the thread's
486 * interrupted status will be cleared.
487 *
488 * <li>Waiting threads are signalled in FIFO order.
489 *
490 * <li>The ordering of lock reacquisition for threads returning
491 * from waiting methods is the same as for threads initially
492 * acquiring the lock, which is in the default case not specified,
493 * but for <em>fair</em> locks favors those threads that have been
494 * waiting the longest.
495 *
496 * </ul>
497 *
498 * @return the Condition object
499 */
500 public Condition newCondition() {
501 return sync.newCondition();
502 }
503
504 /**
505 * Queries the number of holds on this lock by the current thread.
506 *
507 * <p>A thread has a hold on a lock for each lock action that is not
508 * matched by an unlock action.
509 *
510 * <p>The hold count information is typically only used for testing and
511 * debugging purposes. For example, if a certain section of code should
512 * not be entered with the lock already held then we can assert that
513 * fact:
514 *
515 * <pre> {@code
516 * class X {
517 * ReentrantLock lock = new ReentrantLock();
518 * // ...
519 * public void m() {
520 * assert lock.getHoldCount() == 0;
521 * lock.lock();
522 * try {
523 * // ... method body
524 * } finally {
525 * lock.unlock();
526 * }
527 * }
528 * }}</pre>
529 *
530 * @return the number of holds on this lock by the current thread,
531 * or zero if this lock is not held by the current thread
532 */
533 public int getHoldCount() {
534 return sync.getHoldCount();
535 }
536
537 /**
538 * Queries if this lock is held by the current thread.
539 *
540 * <p>Analogous to the {@link Thread#holdsLock(Object)} method for
541 * built-in monitor locks, this method is typically used for
542 * debugging and testing. For example, a method that should only be
543 * called while a lock is held can assert that this is the case:
544 *
545 * <pre> {@code
546 * class X {
547 * ReentrantLock lock = new ReentrantLock();
548 * // ...
549 *
550 * public void m() {
551 * assert lock.isHeldByCurrentThread();
552 * // ... method body
553 * }
554 * }}</pre>
555 *
556 * <p>It can also be used to ensure that a reentrant lock is used
557 * in a non-reentrant manner, for example:
558 *
559 * <pre> {@code
560 * class X {
561 * ReentrantLock lock = new ReentrantLock();
562 * // ...
563 *
564 * public void m() {
565 * assert !lock.isHeldByCurrentThread();
566 * lock.lock();
567 * try {
568 * // ... method body
569 * } finally {
570 * lock.unlock();
571 * }
572 * }
573 * }}</pre>
574 *
575 * @return {@code true} if current thread holds this lock and
576 * {@code false} otherwise
577 */
578 public boolean isHeldByCurrentThread() {
579 return sync.isHeldExclusively();
580 }
581
582 /**
583 * Queries if this lock is held by any thread. This method is
584 * designed for use in monitoring of the system state,
585 * not for synchronization control.
586 *
587 * @return {@code true} if any thread holds this lock and
588 * {@code false} otherwise
589 */
590 public boolean isLocked() {
591 return sync.isLocked();
592 }
593
594 /**
595 * Returns {@code true} if this lock has fairness set true.
596 *
597 * @return {@code true} if this lock has fairness set true
598 */
599 public final boolean isFair() {
600 return sync instanceof FairSync;
601 }
602
603 /**
604 * Returns the thread that currently owns this lock, or
605 * {@code null} if not owned. When this method is called by a
606 * thread that is not the owner, the return value reflects a
607 * best-effort approximation of current lock status. For example,
608 * the owner may be momentarily {@code null} even if there are
609 * threads trying to acquire the lock but have not yet done so.
610 * This method is designed to facilitate construction of
611 * subclasses that provide more extensive lock monitoring
612 * facilities.
613 *
614 * @return the owner, or {@code null} if not owned
615 */
616 protected Thread getOwner() {
617 return sync.getOwner();
618 }
619
620 /**
621 * Queries whether any threads are waiting to acquire this lock. Note that
622 * because cancellations may occur at any time, a {@code true}
623 * return does not guarantee that any other thread will ever
624 * acquire this lock. This method is designed primarily for use in
625 * monitoring of the system state.
626 *
627 * @return {@code true} if there may be other threads waiting to
628 * acquire the lock
629 */
630 public final boolean hasQueuedThreads() {
631 return sync.hasQueuedThreads();
632 }
633
634 /**
635 * Queries whether the given thread is waiting to acquire this
636 * lock. Note that because cancellations may occur at any time, a
637 * {@code true} return does not guarantee that this thread
638 * will ever acquire this lock. This method is designed primarily for use
639 * in monitoring of the system state.
640 *
641 * @param thread the thread
642 * @return {@code true} if the given thread is queued waiting for this lock
643 * @throws NullPointerException if the thread is null
644 */
645 public final boolean hasQueuedThread(Thread thread) {
646 return sync.isQueued(thread);
647 }
648
649 /**
650 * Returns an estimate of the number of threads waiting to acquire
651 * this lock. The value is only an estimate because the number of
652 * threads may change dynamically while this method traverses
653 * internal data structures. This method is designed for use in
654 * monitoring system state, not for synchronization control.
655 *
656 * @return the estimated number of threads waiting for this lock
657 */
658 public final int getQueueLength() {
659 return sync.getQueueLength();
660 }
661
662 /**
663 * Returns a collection containing threads that may be waiting to
664 * acquire this lock. Because the actual set of threads may change
665 * dynamically while constructing this result, the returned
666 * collection is only a best-effort estimate. The elements of the
667 * returned collection are in no particular order. This method is
668 * designed to facilitate construction of subclasses that provide
669 * more extensive monitoring facilities.
670 *
671 * @return the collection of threads
672 */
673 protected Collection<Thread> getQueuedThreads() {
674 return sync.getQueuedThreads();
675 }
676
677 /**
678 * Queries whether any threads are waiting on the given condition
679 * associated with this lock. Note that because timeouts and
680 * interrupts may occur at any time, a {@code true} return does
681 * not guarantee that a future {@code signal} will awaken any
682 * threads. This method is designed primarily for use in
683 * monitoring of the system state.
684 *
685 * @param condition the condition
686 * @return {@code true} if there are any waiting threads
687 * @throws IllegalMonitorStateException if this lock is not held
688 * @throws IllegalArgumentException if the given condition is
689 * not associated with this lock
690 * @throws NullPointerException if the condition is null
691 */
692 public boolean hasWaiters(Condition condition) {
693 if (condition == null)
694 throw new NullPointerException();
695 if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
696 throw new IllegalArgumentException("not owner");
697 return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
698 }
699
700 /**
701 * Returns an estimate of the number of threads waiting on the
702 * given condition associated with this lock. Note that because
703 * timeouts and interrupts may occur at any time, the estimate
704 * serves only as an upper bound on the actual number of waiters.
705 * This method is designed for use in monitoring of the system
706 * state, not for synchronization control.
707 *
708 * @param condition the condition
709 * @return the estimated number of waiting threads
710 * @throws IllegalMonitorStateException if this lock is not held
711 * @throws IllegalArgumentException if the given condition is
712 * not associated with this lock
713 * @throws NullPointerException if the condition is null
714 */
715 public int getWaitQueueLength(Condition condition) {
716 if (condition == null)
717 throw new NullPointerException();
718 if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
719 throw new IllegalArgumentException("not owner");
720 return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
721 }
722
723 /**
724 * Returns a collection containing those threads that may be
725 * waiting on the given condition associated with this lock.
726 * Because the actual set of threads may change dynamically while
727 * constructing this result, the returned collection is only a
728 * best-effort estimate. The elements of the returned collection
729 * are in no particular order. This method is designed to
730 * facilitate construction of subclasses that provide more
731 * extensive condition monitoring facilities.
732 *
733 * @param condition the condition
734 * @return the collection of threads
735 * @throws IllegalMonitorStateException if this lock is not held
736 * @throws IllegalArgumentException if the given condition is
737 * not associated with this lock
738 * @throws NullPointerException if the condition is null
739 */
740 protected Collection<Thread> getWaitingThreads(Condition condition) {
741 if (condition == null)
742 throw new NullPointerException();
743 if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
744 throw new IllegalArgumentException("not owner");
745 return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
746 }
747
748 /**
749 * Returns a string identifying this lock, as well as its lock state.
750 * The state, in brackets, includes either the String {@code "Unlocked"}
751 * or the String {@code "Locked by"} followed by the
752 * {@linkplain Thread#getName name} of the owning thread.
753 *
754 * @return a string identifying this lock, as well as its lock state
755 */
756 public String toString() {
757 Thread o = sync.getOwner();
758 return super.toString() + ((o == null) ?
759 "[Unlocked]" :
760 "[Locked by thread " + o.getName() + "]");
761 }
762 }