| /* |
| * 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. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.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/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent.locks; |
| |
| import java.util.Collection; |
| import java.util.concurrent.TimeUnit; |
| import jdk.internal.vm.annotation.ReservedStackAccess; |
| |
| /** |
| * 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()} 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> {@code |
| * 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 a number of {@code public} and {@code protected} |
| * methods for inspecting the state of the lock. Some of these |
| * methods are only 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. |
| */ |
| abstract static class Sync extends AbstractQueuedSynchronizer { |
| private static final long serialVersionUID = -5179523762034025860L; |
| |
| /** |
| * Performs non-fair tryLock. |
| */ |
| @ReservedStackAccess |
| final boolean tryLock() { |
| Thread current = Thread.currentThread(); |
| int c = getState(); |
| if (c == 0) { |
| if (compareAndSetState(0, 1)) { |
| setExclusiveOwnerThread(current); |
| return true; |
| } |
| } else if (getExclusiveOwnerThread() == current) { |
| if (++c < 0) // overflow |
| throw new Error("Maximum lock count exceeded"); |
| setState(c); |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Checks for reentrancy and acquires if lock immediately |
| * available under fair vs nonfair rules. Locking methods |
| * perform initialTryLock check before relaying to |
| * corresponding AQS acquire methods. |
| */ |
| abstract boolean initialTryLock(); |
| |
| @ReservedStackAccess |
| final void lock() { |
| if (!initialTryLock()) |
| acquire(1); |
| } |
| |
| @ReservedStackAccess |
| final void lockInterruptibly() throws InterruptedException { |
| if (Thread.interrupted()) |
| throw new InterruptedException(); |
| if (!initialTryLock()) |
| acquireInterruptibly(1); |
| } |
| |
| @ReservedStackAccess |
| final boolean tryLockNanos(long nanos) throws InterruptedException { |
| if (Thread.interrupted()) |
| throw new InterruptedException(); |
| return initialTryLock() || tryAcquireNanos(1, nanos); |
| } |
| |
| @ReservedStackAccess |
| protected final boolean tryRelease(int releases) { |
| int c = getState() - releases; |
| if (getExclusiveOwnerThread() != Thread.currentThread()) |
| throw new IllegalMonitorStateException(); |
| boolean free = (c == 0); |
| if (free) |
| 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 the instance from a stream (that is, deserializes it). |
| */ |
| 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 |
| */ |
| static final class NonfairSync extends Sync { |
| private static final long serialVersionUID = 7316153563782823691L; |
| |
| final boolean initialTryLock() { |
| Thread current = Thread.currentThread(); |
| if (compareAndSetState(0, 1)) { // first attempt is unguarded |
| setExclusiveOwnerThread(current); |
| return true; |
| } else if (getExclusiveOwnerThread() == current) { |
| int c = getState() + 1; |
| if (c < 0) // overflow |
| throw new Error("Maximum lock count exceeded"); |
| setState(c); |
| return true; |
| } else |
| return false; |
| } |
| |
| /** |
| * Acquire for non-reentrant cases after initialTryLock prescreen |
| */ |
| protected final boolean tryAcquire(int acquires) { |
| if (getState() == 0 && compareAndSetState(0, acquires)) { |
| setExclusiveOwnerThread(Thread.currentThread()); |
| return true; |
| } |
| return false; |
| } |
| } |
| |
| /** |
| * Sync object for fair locks |
| */ |
| static final class FairSync extends Sync { |
| private static final long serialVersionUID = -3000897897090466540L; |
| |
| /** |
| * Acquires only if reentrant or queue is empty. |
| */ |
| final boolean initialTryLock() { |
| Thread current = Thread.currentThread(); |
| int c = getState(); |
| if (c == 0) { |
| if (!hasQueuedThreads() && compareAndSetState(0, 1)) { |
| setExclusiveOwnerThread(current); |
| return true; |
| } |
| } else if (getExclusiveOwnerThread() == current) { |
| if (++c < 0) // overflow |
| throw new Error("Maximum lock count exceeded"); |
| setState(c); |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Acquires only if thread is first waiter or empty |
| */ |
| protected final boolean tryAcquire(int acquires) { |
| if (getState() == 0 && !hasQueuedPredecessors() && |
| compareAndSetState(0, acquires)) { |
| setExclusiveOwnerThread(Thread.currentThread()); |
| 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.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 "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.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> {@code |
| * 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.tryLockNanos(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> {@code |
| * class X { |
| * final 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(Object)} 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> {@code |
| * class X { |
| * final 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> {@code |
| * class X { |
| * final 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 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() + "]"); |
| } |
| } |
