jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent.locks;
jaroslav@1890: import java.util.*;
jaroslav@1890: import java.util.concurrent.*;
jaroslav@1890: import java.util.concurrent.atomic.*;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * A reentrant mutual exclusion {@link Lock} with the same basic
jaroslav@1890:  * behavior and semantics as the implicit monitor lock accessed using
jaroslav@1890:  * {@code synchronized} methods and statements, but with extended
jaroslav@1890:  * capabilities.
jaroslav@1890:  *
jaroslav@1890:  * <p>A {@code ReentrantLock} is <em>owned</em> by the thread last
jaroslav@1890:  * successfully locking, but not yet unlocking it. A thread invoking
jaroslav@1890:  * {@code lock} will return, successfully acquiring the lock, when
jaroslav@1890:  * the lock is not owned by another thread. The method will return
jaroslav@1890:  * immediately if the current thread already owns the lock. This can
jaroslav@1890:  * be checked using methods {@link #isHeldByCurrentThread}, and {@link
jaroslav@1890:  * #getHoldCount}.
jaroslav@1890:  *
jaroslav@1890:  * <p>The constructor for this class accepts an optional
jaroslav@1890:  * <em>fairness</em> parameter.  When set {@code true}, under
jaroslav@1890:  * contention, locks favor granting access to the longest-waiting
jaroslav@1890:  * thread.  Otherwise this lock does not guarantee any particular
jaroslav@1890:  * access order.  Programs using fair locks accessed by many threads
jaroslav@1890:  * may display lower overall throughput (i.e., are slower; often much
jaroslav@1890:  * slower) than those using the default setting, but have smaller
jaroslav@1890:  * variances in times to obtain locks and guarantee lack of
jaroslav@1890:  * starvation. Note however, that fairness of locks does not guarantee
jaroslav@1890:  * fairness of thread scheduling. Thus, one of many threads using a
jaroslav@1890:  * fair lock may obtain it multiple times in succession while other
jaroslav@1890:  * active threads are not progressing and not currently holding the
jaroslav@1890:  * lock.
jaroslav@1890:  * Also note that the untimed {@link #tryLock() tryLock} method does not
jaroslav@1890:  * honor the fairness setting. It will succeed if the lock
jaroslav@1890:  * is available even if other threads are waiting.
jaroslav@1890:  *
jaroslav@1890:  * <p>It is recommended practice to <em>always</em> immediately
jaroslav@1890:  * follow a call to {@code lock} with a {@code try} block, most
jaroslav@1890:  * typically in a before/after construction such as:
jaroslav@1890:  *
jaroslav@1890:  * <pre>
jaroslav@1890:  * class X {
jaroslav@1890:  *   private final ReentrantLock lock = new ReentrantLock();
jaroslav@1890:  *   // ...
jaroslav@1890:  *
jaroslav@1890:  *   public void m() {
jaroslav@1890:  *     lock.lock();  // block until condition holds
jaroslav@1890:  *     try {
jaroslav@1890:  *       // ... method body
jaroslav@1890:  *     } finally {
jaroslav@1890:  *       lock.unlock()
jaroslav@1890:  *     }
jaroslav@1890:  *   }
jaroslav@1890:  * }
jaroslav@1890:  * </pre>
jaroslav@1890:  *
jaroslav@1890:  * <p>In addition to implementing the {@link Lock} interface, this
jaroslav@1890:  * class defines methods {@code isLocked} and
jaroslav@1890:  * {@code getLockQueueLength}, as well as some associated
jaroslav@1890:  * {@code protected} access methods that may be useful for
jaroslav@1890:  * instrumentation and monitoring.
jaroslav@1890:  *
jaroslav@1890:  * <p>Serialization of this class behaves in the same way as built-in
jaroslav@1890:  * locks: a deserialized lock is in the unlocked state, regardless of
jaroslav@1890:  * its state when serialized.
jaroslav@1890:  *
jaroslav@1890:  * <p>This lock supports a maximum of 2147483647 recursive locks by
jaroslav@1890:  * the same thread. Attempts to exceed this limit result in
jaroslav@1890:  * {@link Error} throws from locking methods.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.5
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  */
jaroslav@1890: public class ReentrantLock implements Lock, java.io.Serializable {
jaroslav@1890:     private static final long serialVersionUID = 7373984872572414699L;
jaroslav@1890:     /** Synchronizer providing all implementation mechanics */
jaroslav@1890:     private final Sync sync;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Base of synchronization control for this lock. Subclassed
jaroslav@1890:      * into fair and nonfair versions below. Uses AQS state to
jaroslav@1890:      * represent the number of holds on the lock.
jaroslav@1890:      */
jaroslav@1890:     abstract static class Sync extends AbstractQueuedSynchronizer {
jaroslav@1890:         private static final long serialVersionUID = -5179523762034025860L;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Performs {@link Lock#lock}. The main reason for subclassing
jaroslav@1890:          * is to allow fast path for nonfair version.
jaroslav@1890:          */
jaroslav@1890:         abstract void lock();
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Performs non-fair tryLock.  tryAcquire is
jaroslav@1890:          * implemented in subclasses, but both need nonfair
jaroslav@1890:          * try for trylock method.
jaroslav@1890:          */
jaroslav@1890:         final boolean nonfairTryAcquire(int acquires) {
jaroslav@1890:             final Thread current = Thread.currentThread();
jaroslav@1890:             int c = getState();
jaroslav@1890:             if (c == 0) {
jaroslav@1890:                 if (compareAndSetState(0, acquires)) {
jaroslav@1890:                     setExclusiveOwnerThread(current);
jaroslav@1890:                     return true;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:             else if (current == getExclusiveOwnerThread()) {
jaroslav@1890:                 int nextc = c + acquires;
jaroslav@1890:                 if (nextc < 0) // overflow
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:                 setState(nextc);
jaroslav@1890:                 return true;
jaroslav@1890:             }
jaroslav@1890:             return false;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean tryRelease(int releases) {
jaroslav@1890:             int c = getState() - releases;
jaroslav@1890:             if (Thread.currentThread() != getExclusiveOwnerThread())
jaroslav@1890:                 throw new IllegalMonitorStateException();
jaroslav@1890:             boolean free = false;
jaroslav@1890:             if (c == 0) {
jaroslav@1890:                 free = true;
jaroslav@1890:                 setExclusiveOwnerThread(null);
jaroslav@1890:             }
jaroslav@1890:             setState(c);
jaroslav@1890:             return free;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean isHeldExclusively() {
jaroslav@1890:             // While we must in general read state before owner,
jaroslav@1890:             // we don't need to do so to check if current thread is owner
jaroslav@1890:             return getExclusiveOwnerThread() == Thread.currentThread();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final ConditionObject newCondition() {
jaroslav@1890:             return new ConditionObject();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         // Methods relayed from outer class
jaroslav@1890: 
jaroslav@1890:         final Thread getOwner() {
jaroslav@1890:             return getState() == 0 ? null : getExclusiveOwnerThread();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final int getHoldCount() {
jaroslav@1890:             return isHeldExclusively() ? getState() : 0;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final boolean isLocked() {
jaroslav@1890:             return getState() != 0;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Reconstitutes this lock instance from a stream.
jaroslav@1890:          * @param s the stream
jaroslav@1890:          */
jaroslav@1890:         private void readObject(java.io.ObjectInputStream s)
jaroslav@1890:             throws java.io.IOException, ClassNotFoundException {
jaroslav@1890:             s.defaultReadObject();
jaroslav@1890:             setState(0); // reset to unlocked state
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Sync object for non-fair locks
jaroslav@1890:      */
jaroslav@1890:     static final class NonfairSync extends Sync {
jaroslav@1890:         private static final long serialVersionUID = 7316153563782823691L;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Performs lock.  Try immediate barge, backing up to normal
jaroslav@1890:          * acquire on failure.
jaroslav@1890:          */
jaroslav@1890:         final void lock() {
jaroslav@1890:             if (compareAndSetState(0, 1))
jaroslav@1890:                 setExclusiveOwnerThread(Thread.currentThread());
jaroslav@1890:             else
jaroslav@1890:                 acquire(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean tryAcquire(int acquires) {
jaroslav@1890:             return nonfairTryAcquire(acquires);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Sync object for fair locks
jaroslav@1890:      */
jaroslav@1890:     static final class FairSync extends Sync {
jaroslav@1890:         private static final long serialVersionUID = -3000897897090466540L;
jaroslav@1890: 
jaroslav@1890:         final void lock() {
jaroslav@1890:             acquire(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Fair version of tryAcquire.  Don't grant access unless
jaroslav@1890:          * recursive call or no waiters or is first.
jaroslav@1890:          */
jaroslav@1890:         protected final boolean tryAcquire(int acquires) {
jaroslav@1890:             final Thread current = Thread.currentThread();
jaroslav@1890:             int c = getState();
jaroslav@1890:             if (c == 0) {
jaroslav@1890:                 if (!hasQueuedPredecessors() &&
jaroslav@1890:                     compareAndSetState(0, acquires)) {
jaroslav@1890:                     setExclusiveOwnerThread(current);
jaroslav@1890:                     return true;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:             else if (current == getExclusiveOwnerThread()) {
jaroslav@1890:                 int nextc = c + acquires;
jaroslav@1890:                 if (nextc < 0)
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:                 setState(nextc);
jaroslav@1890:                 return true;
jaroslav@1890:             }
jaroslav@1890:             return false;
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates an instance of {@code ReentrantLock}.
jaroslav@1890:      * This is equivalent to using {@code ReentrantLock(false)}.
jaroslav@1890:      */
jaroslav@1890:     public ReentrantLock() {
jaroslav@1890:         sync = new NonfairSync();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates an instance of {@code ReentrantLock} with the
jaroslav@1890:      * given fairness policy.
jaroslav@1890:      *
jaroslav@1890:      * @param fair {@code true} if this lock should use a fair ordering policy
jaroslav@1890:      */
jaroslav@1890:     public ReentrantLock(boolean fair) {
jaroslav@1890:         sync = fair ? new FairSync() : new NonfairSync();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Acquires the lock.
jaroslav@1890:      *
jaroslav@1890:      * <p>Acquires the lock if it is not held by another thread and returns
jaroslav@1890:      * immediately, setting the lock hold count to one.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread already holds the lock then the hold
jaroslav@1890:      * count is incremented by one and the method returns immediately.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is held by another thread then the
jaroslav@1890:      * current thread becomes disabled for thread scheduling
jaroslav@1890:      * purposes and lies dormant until the lock has been acquired,
jaroslav@1890:      * at which time the lock hold count is set to one.
jaroslav@1890:      */
jaroslav@1890:     public void lock() {
jaroslav@1890:         sync.lock();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Acquires the lock unless the current thread is
jaroslav@1890:      * {@linkplain Thread#interrupt interrupted}.
jaroslav@1890:      *
jaroslav@1890:      * <p>Acquires the lock if it is not held by another thread and returns
jaroslav@1890:      * immediately, setting the lock hold count to one.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread already holds this lock then the hold count
jaroslav@1890:      * is incremented by one and the method returns immediately.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is held by another thread then the
jaroslav@1890:      * current thread becomes disabled for thread scheduling
jaroslav@1890:      * purposes and lies dormant until one of two things happens:
jaroslav@1890:      *
jaroslav@1890:      * <ul>
jaroslav@1890:      *
jaroslav@1890:      * <li>The lock is acquired by the current thread; or
jaroslav@1890:      *
jaroslav@1890:      * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
jaroslav@1890:      * current thread.
jaroslav@1890:      *
jaroslav@1890:      * </ul>
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is acquired by the current thread then the lock hold
jaroslav@1890:      * count is set to one.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread:
jaroslav@1890:      *
jaroslav@1890:      * <ul>
jaroslav@1890:      *
jaroslav@1890:      * <li>has its interrupted status set on entry to this method; or
jaroslav@1890:      *
jaroslav@1890:      * <li>is {@linkplain Thread#interrupt interrupted} while acquiring
jaroslav@1890:      * the lock,
jaroslav@1890:      *
jaroslav@1890:      * </ul>
jaroslav@1890:      *
jaroslav@1890:      * then {@link InterruptedException} is thrown and the current thread's
jaroslav@1890:      * interrupted status is cleared.
jaroslav@1890:      *
jaroslav@1890:      * <p>In this implementation, as this method is an explicit
jaroslav@1890:      * interruption point, preference is given to responding to the
jaroslav@1890:      * interrupt over normal or reentrant acquisition of the lock.
jaroslav@1890:      *
jaroslav@1890:      * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:      */
jaroslav@1890:     public void lockInterruptibly() throws InterruptedException {
jaroslav@1890:         sync.acquireInterruptibly(1);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Acquires the lock only if it is not held by another thread at the time
jaroslav@1890:      * of invocation.
jaroslav@1890:      *
jaroslav@1890:      * <p>Acquires the lock if it is not held by another thread and
jaroslav@1890:      * returns immediately with the value {@code true}, setting the
jaroslav@1890:      * lock hold count to one. Even when this lock has been set to use a
jaroslav@1890:      * fair ordering policy, a call to {@code tryLock()} <em>will</em>
jaroslav@1890:      * immediately acquire the lock if it is available, whether or not
jaroslav@1890:      * other threads are currently waiting for the lock.
jaroslav@1890:      * This &quot;barging&quot; behavior can be useful in certain
jaroslav@1890:      * circumstances, even though it breaks fairness. If you want to honor
jaroslav@1890:      * the fairness setting for this lock, then use
jaroslav@1890:      * {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
jaroslav@1890:      * which is almost equivalent (it also detects interruption).
jaroslav@1890:      *
jaroslav@1890:      * <p> If the current thread already holds this lock then the hold
jaroslav@1890:      * count is incremented by one and the method returns {@code true}.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is held by another thread then this method will return
jaroslav@1890:      * immediately with the value {@code false}.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if the lock was free and was acquired by the
jaroslav@1890:      *         current thread, or the lock was already held by the current
jaroslav@1890:      *         thread; and {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public boolean tryLock() {
jaroslav@1890:         return sync.nonfairTryAcquire(1);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Acquires the lock if it is not held by another thread within the given
jaroslav@1890:      * waiting time and the current thread has not been
jaroslav@1890:      * {@linkplain Thread#interrupt interrupted}.
jaroslav@1890:      *
jaroslav@1890:      * <p>Acquires the lock if it is not held by another thread and returns
jaroslav@1890:      * immediately with the value {@code true}, setting the lock hold count
jaroslav@1890:      * to one. If this lock has been set to use a fair ordering policy then
jaroslav@1890:      * an available lock <em>will not</em> be acquired if any other threads
jaroslav@1890:      * are waiting for the lock. This is in contrast to the {@link #tryLock()}
jaroslav@1890:      * method. If you want a timed {@code tryLock} that does permit barging on
jaroslav@1890:      * a fair lock then combine the timed and un-timed forms together:
jaroslav@1890:      *
jaroslav@1890:      * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
jaroslav@1890:      * </pre>
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread
jaroslav@1890:      * already holds this lock then the hold count is incremented by one and
jaroslav@1890:      * the method returns {@code true}.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is held by another thread then the
jaroslav@1890:      * current thread becomes disabled for thread scheduling
jaroslav@1890:      * purposes and lies dormant until one of three things happens:
jaroslav@1890:      *
jaroslav@1890:      * <ul>
jaroslav@1890:      *
jaroslav@1890:      * <li>The lock is acquired by the current thread; or
jaroslav@1890:      *
jaroslav@1890:      * <li>Some other thread {@linkplain Thread#interrupt interrupts}
jaroslav@1890:      * the current thread; or
jaroslav@1890:      *
jaroslav@1890:      * <li>The specified waiting time elapses
jaroslav@1890:      *
jaroslav@1890:      * </ul>
jaroslav@1890:      *
jaroslav@1890:      * <p>If the lock is acquired then the value {@code true} is returned and
jaroslav@1890:      * the lock hold count is set to one.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread:
jaroslav@1890:      *
jaroslav@1890:      * <ul>
jaroslav@1890:      *
jaroslav@1890:      * <li>has its interrupted status set on entry to this method; or
jaroslav@1890:      *
jaroslav@1890:      * <li>is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:      * acquiring the lock,
jaroslav@1890:      *
jaroslav@1890:      * </ul>
jaroslav@1890:      * then {@link InterruptedException} is thrown and the current thread's
jaroslav@1890:      * interrupted status is cleared.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the specified waiting time elapses then the value {@code false}
jaroslav@1890:      * is returned.  If the time is less than or equal to zero, the method
jaroslav@1890:      * will not wait at all.
jaroslav@1890:      *
jaroslav@1890:      * <p>In this implementation, as this method is an explicit
jaroslav@1890:      * interruption point, preference is given to responding to the
jaroslav@1890:      * interrupt over normal or reentrant acquisition of the lock, and
jaroslav@1890:      * over reporting the elapse of the waiting time.
jaroslav@1890:      *
jaroslav@1890:      * @param timeout the time to wait for the lock
jaroslav@1890:      * @param unit the time unit of the timeout argument
jaroslav@1890:      * @return {@code true} if the lock was free and was acquired by the
jaroslav@1890:      *         current thread, or the lock was already held by the current
jaroslav@1890:      *         thread; and {@code false} if the waiting time elapsed before
jaroslav@1890:      *         the lock could be acquired
jaroslav@1890:      * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:      * @throws NullPointerException if the time unit is null
jaroslav@1890:      *
jaroslav@1890:      */
jaroslav@1890:     public boolean tryLock(long timeout, TimeUnit unit)
jaroslav@1890:             throws InterruptedException {
jaroslav@1890:         return sync.tryAcquireNanos(1, unit.toNanos(timeout));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Attempts to release this lock.
jaroslav@1890:      *
jaroslav@1890:      * <p>If the current thread is the holder of this lock then the hold
jaroslav@1890:      * count is decremented.  If the hold count is now zero then the lock
jaroslav@1890:      * is released.  If the current thread is not the holder of this
jaroslav@1890:      * lock then {@link IllegalMonitorStateException} is thrown.
jaroslav@1890:      *
jaroslav@1890:      * @throws IllegalMonitorStateException if the current thread does not
jaroslav@1890:      *         hold this lock
jaroslav@1890:      */
jaroslav@1890:     public void unlock() {
jaroslav@1890:         sync.release(1);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a {@link Condition} instance for use with this
jaroslav@1890:      * {@link Lock} instance.
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned {@link Condition} instance supports the same
jaroslav@1890:      * usages as do the {@link Object} monitor methods ({@link
jaroslav@1890:      * Object#wait() wait}, {@link Object#notify notify}, and {@link
jaroslav@1890:      * Object#notifyAll notifyAll}) when used with the built-in
jaroslav@1890:      * monitor lock.
jaroslav@1890:      *
jaroslav@1890:      * <ul>
jaroslav@1890:      *
jaroslav@1890:      * <li>If this lock is not held when any of the {@link Condition}
jaroslav@1890:      * {@linkplain Condition#await() waiting} or {@linkplain
jaroslav@1890:      * Condition#signal signalling} methods are called, then an {@link
jaroslav@1890:      * IllegalMonitorStateException} is thrown.
jaroslav@1890:      *
jaroslav@1890:      * <li>When the condition {@linkplain Condition#await() waiting}
jaroslav@1890:      * methods are called the lock is released and, before they
jaroslav@1890:      * return, the lock is reacquired and the lock hold count restored
jaroslav@1890:      * to what it was when the method was called.
jaroslav@1890:      *
jaroslav@1890:      * <li>If a thread is {@linkplain Thread#interrupt interrupted}
jaroslav@1890:      * while waiting then the wait will terminate, an {@link
jaroslav@1890:      * InterruptedException} will be thrown, and the thread's
jaroslav@1890:      * interrupted status will be cleared.
jaroslav@1890:      *
jaroslav@1890:      * <li> Waiting threads are signalled in FIFO order.
jaroslav@1890:      *
jaroslav@1890:      * <li>The ordering of lock reacquisition for threads returning
jaroslav@1890:      * from waiting methods is the same as for threads initially
jaroslav@1890:      * acquiring the lock, which is in the default case not specified,
jaroslav@1890:      * but for <em>fair</em> locks favors those threads that have been
jaroslav@1890:      * waiting the longest.
jaroslav@1890:      *
jaroslav@1890:      * </ul>
jaroslav@1890:      *
jaroslav@1890:      * @return the Condition object
jaroslav@1890:      */
jaroslav@1890:     public Condition newCondition() {
jaroslav@1890:         return sync.newCondition();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries the number of holds on this lock by the current thread.
jaroslav@1890:      *
jaroslav@1890:      * <p>A thread has a hold on a lock for each lock action that is not
jaroslav@1890:      * matched by an unlock action.
jaroslav@1890:      *
jaroslav@1890:      * <p>The hold count information is typically only used for testing and
jaroslav@1890:      * debugging purposes. For example, if a certain section of code should
jaroslav@1890:      * not be entered with the lock already held then we can assert that
jaroslav@1890:      * fact:
jaroslav@1890:      *
jaroslav@1890:      * <pre>
jaroslav@1890:      * class X {
jaroslav@1890:      *   ReentrantLock lock = new ReentrantLock();
jaroslav@1890:      *   // ...
jaroslav@1890:      *   public void m() {
jaroslav@1890:      *     assert lock.getHoldCount() == 0;
jaroslav@1890:      *     lock.lock();
jaroslav@1890:      *     try {
jaroslav@1890:      *       // ... method body
jaroslav@1890:      *     } finally {
jaroslav@1890:      *       lock.unlock();
jaroslav@1890:      *     }
jaroslav@1890:      *   }
jaroslav@1890:      * }
jaroslav@1890:      * </pre>
jaroslav@1890:      *
jaroslav@1890:      * @return the number of holds on this lock by the current thread,
jaroslav@1890:      *         or zero if this lock is not held by the current thread
jaroslav@1890:      */
jaroslav@1890:     public int getHoldCount() {
jaroslav@1890:         return sync.getHoldCount();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries if this lock is held by the current thread.
jaroslav@1890:      *
jaroslav@1890:      * <p>Analogous to the {@link Thread#holdsLock} method for built-in
jaroslav@1890:      * monitor locks, this method is typically used for debugging and
jaroslav@1890:      * testing. For example, a method that should only be called while
jaroslav@1890:      * a lock is held can assert that this is the case:
jaroslav@1890:      *
jaroslav@1890:      * <pre>
jaroslav@1890:      * class X {
jaroslav@1890:      *   ReentrantLock lock = new ReentrantLock();
jaroslav@1890:      *   // ...
jaroslav@1890:      *
jaroslav@1890:      *   public void m() {
jaroslav@1890:      *       assert lock.isHeldByCurrentThread();
jaroslav@1890:      *       // ... method body
jaroslav@1890:      *   }
jaroslav@1890:      * }
jaroslav@1890:      * </pre>
jaroslav@1890:      *
jaroslav@1890:      * <p>It can also be used to ensure that a reentrant lock is used
jaroslav@1890:      * in a non-reentrant manner, for example:
jaroslav@1890:      *
jaroslav@1890:      * <pre>
jaroslav@1890:      * class X {
jaroslav@1890:      *   ReentrantLock lock = new ReentrantLock();
jaroslav@1890:      *   // ...
jaroslav@1890:      *
jaroslav@1890:      *   public void m() {
jaroslav@1890:      *       assert !lock.isHeldByCurrentThread();
jaroslav@1890:      *       lock.lock();
jaroslav@1890:      *       try {
jaroslav@1890:      *           // ... method body
jaroslav@1890:      *       } finally {
jaroslav@1890:      *           lock.unlock();
jaroslav@1890:      *       }
jaroslav@1890:      *   }
jaroslav@1890:      * }
jaroslav@1890:      * </pre>
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if current thread holds this lock and
jaroslav@1890:      *         {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public boolean isHeldByCurrentThread() {
jaroslav@1890:         return sync.isHeldExclusively();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries if this lock is held by any thread. This method is
jaroslav@1890:      * designed for use in monitoring of the system state,
jaroslav@1890:      * not for synchronization control.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if any thread holds this lock and
jaroslav@1890:      *         {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public boolean isLocked() {
jaroslav@1890:         return sync.isLocked();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this lock has fairness set true.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if this lock has fairness set true
jaroslav@1890:      */
jaroslav@1890:     public final boolean isFair() {
jaroslav@1890:         return sync instanceof FairSync;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the thread that currently owns this lock, or
jaroslav@1890:      * {@code null} if not owned. When this method is called by a
jaroslav@1890:      * thread that is not the owner, the return value reflects a
jaroslav@1890:      * best-effort approximation of current lock status. For example,
jaroslav@1890:      * the owner may be momentarily {@code null} even if there are
jaroslav@1890:      * threads trying to acquire the lock but have not yet done so.
jaroslav@1890:      * This method is designed to facilitate construction of
jaroslav@1890:      * subclasses that provide more extensive lock monitoring
jaroslav@1890:      * facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the owner, or {@code null} if not owned
jaroslav@1890:      */
jaroslav@1890:     protected Thread getOwner() {
jaroslav@1890:         return sync.getOwner();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether any threads are waiting to acquire this lock. Note that
jaroslav@1890:      * because cancellations may occur at any time, a {@code true}
jaroslav@1890:      * return does not guarantee that any other thread will ever
jaroslav@1890:      * acquire this lock.  This method is designed primarily for use in
jaroslav@1890:      * monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if there may be other threads waiting to
jaroslav@1890:      *         acquire the lock
jaroslav@1890:      */
jaroslav@1890:     public final boolean hasQueuedThreads() {
jaroslav@1890:         return sync.hasQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether the given thread is waiting to acquire this
jaroslav@1890:      * lock. Note that because cancellations may occur at any time, a
jaroslav@1890:      * {@code true} return does not guarantee that this thread
jaroslav@1890:      * will ever acquire this lock.  This method is designed primarily for use
jaroslav@1890:      * in monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @param thread the thread
jaroslav@1890:      * @return {@code true} if the given thread is queued waiting for this lock
jaroslav@1890:      * @throws NullPointerException if the thread is null
jaroslav@1890:      */
jaroslav@1890:     public final boolean hasQueuedThread(Thread thread) {
jaroslav@1890:         return sync.isQueued(thread);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of the number of threads waiting to
jaroslav@1890:      * acquire this lock.  The value is only an estimate because the number of
jaroslav@1890:      * threads may change dynamically while this method traverses
jaroslav@1890:      * internal data structures.  This method is designed for use in
jaroslav@1890:      * monitoring of the system state, not for synchronization
jaroslav@1890:      * control.
jaroslav@1890:      *
jaroslav@1890:      * @return the estimated number of threads waiting for this lock
jaroslav@1890:      */
jaroslav@1890:     public final int getQueueLength() {
jaroslav@1890:         return sync.getQueueLength();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing threads that may be waiting to
jaroslav@1890:      * acquire this lock.  Because the actual set of threads may change
jaroslav@1890:      * dynamically while constructing this result, the returned
jaroslav@1890:      * collection is only a best-effort estimate.  The elements of the
jaroslav@1890:      * returned collection are in no particular order.  This method is
jaroslav@1890:      * designed to facilitate construction of subclasses that provide
jaroslav@1890:      * more extensive monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getQueuedThreads() {
jaroslav@1890:         return sync.getQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether any threads are waiting on the given condition
jaroslav@1890:      * associated with this lock. Note that because timeouts and
jaroslav@1890:      * interrupts may occur at any time, a {@code true} return does
jaroslav@1890:      * not guarantee that a future {@code signal} will awaken any
jaroslav@1890:      * threads.  This method is designed primarily for use in
jaroslav@1890:      * monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return {@code true} if there are any waiting threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     public boolean hasWaiters(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of the number of threads waiting on the
jaroslav@1890:      * given condition associated with this lock. Note that because
jaroslav@1890:      * timeouts and interrupts may occur at any time, the estimate
jaroslav@1890:      * serves only as an upper bound on the actual number of waiters.
jaroslav@1890:      * This method is designed for use in monitoring of the system
jaroslav@1890:      * state, not for synchronization control.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return the estimated number of waiting threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     public int getWaitQueueLength(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing those threads that may be
jaroslav@1890:      * waiting on the given condition associated with this lock.
jaroslav@1890:      * Because the actual set of threads may change dynamically while
jaroslav@1890:      * constructing this result, the returned collection is only a
jaroslav@1890:      * best-effort estimate. The elements of the returned collection
jaroslav@1890:      * are in no particular order.  This method is designed to
jaroslav@1890:      * facilitate construction of subclasses that provide more
jaroslav@1890:      * extensive condition monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getWaitingThreads(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a string identifying this lock, as well as its lock state.
jaroslav@1890:      * The state, in brackets, includes either the String {@code "Unlocked"}
jaroslav@1890:      * or the String {@code "Locked by"} followed by the
jaroslav@1890:      * {@linkplain Thread#getName name} of the owning thread.
jaroslav@1890:      *
jaroslav@1890:      * @return a string identifying this lock, as well as its lock state
jaroslav@1890:      */
jaroslav@1890:     public String toString() {
jaroslav@1890:         Thread o = sync.getOwner();
jaroslav@1890:         return super.toString() + ((o == null) ?
jaroslav@1890:                                    "[Unlocked]" :
jaroslav@1890:                                    "[Locked by thread " + o.getName() + "]");
jaroslav@1890:     }
jaroslav@1890: }