/*
 
* 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.concurrent.TimeUnit;
import java.util.Collection;

/**
 
* 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
 
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 {@link Lock#lock}. The main reason for subclassing
         
* is to allow fast path for nonfair version.
         
*/

        
abstract void lock();

        
/**
         
* Performs non-fair tryLock.
  
tryAcquire is implemented in
         
* subclasses, but both need nonfair try for trylock method.
         
*/

        
final boolean nonfairTryAcquire(int acquires) {
            
final Thread current = Thread.currentThread();
            
int c = getState();
            
if (c == 0) {
                
if (compareAndSetState(0, acquires)) {
                    
setExclusiveOwnerThread(current);
                    
return true;
                
}
            
}
            
else if (current == getExclusiveOwnerThread()) {
                
int nextc = c + acquires;
                
if (nextc < 0) // overflow
                    
throw new Error("Maximum lock count exceeded");
                
setState(nextc);
                
return true;
            
}
            
return false;
        
}

        
protected final boolean tryRelease(int releases) {
            
int c = getState() - releases;
            
if (Thread.currentThread() != getExclusiveOwnerThread())
                
throw new IllegalMonitorStateException();
            
boolean free = false;
            
if (c == 0) {
                
free = true;
                
setExclusiveOwnerThread(null);
            
}
            
setState(c);
            
return free;
        
}

        
protected final boolean isHeldExclusively() {
            
// While we must in general read state before owner,
            
// we don't need to do so to check if current thread is owner
            
return getExclusiveOwnerThread() == Thread.currentThread();
        
}

        
final ConditionObject newCondition() {
            
return new ConditionObject();
        
}

        
// Methods relayed from outer class

        
final Thread getOwner() {
            
return getState() == 0 ? null : getExclusiveOwnerThread();
        
}

        
final int getHoldCount() {
            
return isHeldExclusively() ? getState() : 0;
        
}

        
final boolean isLocked() {
            
return getState() != 0;
        
}

        
/**
         
* Reconstitutes 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;

        
/**
         
* Performs lock.
  
Try immediate barge, backing up to normal
         
* acquire on failure.
         
*/

        
final void lock() {
            
if (compareAndSetState(0, 1))
                
setExclusiveOwnerThread(Thread.currentThread());
            
else
                
acquire(1);
        
}

        
protected final boolean tryAcquire(int acquires) {
            
return nonfairTryAcquire(acquires);
        
}
    
}

    
/**
     
* Sync object for fair locks
     
*/
    
static final class FairSync extends Sync {
        
private static final long serialVersionUID = -3000897897090466540L;

        
final void lock() {
            
acquire(1);
        
}

        
/**
         
* Fair version of tryAcquire.
  
Don't grant access unless
         
* recursive call or no waiters or is first.
         
*/

        
protected final boolean tryAcquire(int acquires) {
            
final Thread current = Thread.currentThread();
            
int c = getState();
            
if (c == 0) {
                
if (!hasQueuedPredecessors() &&
                    
compareAndSetState(0, acquires)) {
                    
setExclusiveOwnerThread(current);
                    
return true;
                
}
            
}
            
else if (current == getExclusiveOwnerThread()) {
                
int nextc = c + acquires;
                
if (nextc < 0)
                    
throw new Error("Maximum lock count exceeded");
                
setState(nextc);
                
return true;
            
}
            
return false;
        
}
    
}

    
/**
     
* Creates an instance of {@code ReentrantLock}.
     
* This is equivalent to using {@code ReentrantLock(false)}.
     
*/

    
public ReentrantLock() {
        
sync = new NonfairSync();
    
}

    
/**
     
* Creates an instance of {@code ReentrantLock} with the
     
* given fairness policy.
     
*
     
* @param fair {@code true} if this lock should use a fair ordering policy
     
*/

    
public ReentrantLock(boolean fair) {
        
sync = fair ? new FairSync() : new NonfairSync();
    
}

    
/**
     
* Acquires the lock.
     
*
     
* <p>Acquires the lock if it is not held by another thread and returns
     
* immediately, setting the lock hold count to one.
     
*
     
* <p>If the current thread already holds the lock then the hold
     
* count is incremented by one and the method returns immediately.
     
*
     
* <p>If the lock is held by another thread then the
     
* current thread becomes disabled for thread scheduling
     
* purposes and lies dormant until the lock has been acquired,
     
* at which time the lock hold count is set to one.
     
*/

    
public void lock() {
        
sync.lock();
    
}

    
/**
     
* Acquires the lock unless the current thread is
     
* {@linkplain Thread#interrupt interrupted}.
     
*
     
* <p>Acquires the lock if it is not held by another thread and returns
     
* immediately, setting the lock hold count to one.
     
*
     
* <p>If the current thread already holds this lock then the hold count
     
* is incremented by one and the method returns immediately.
     
*
     
* <p>If the lock is held by another thread then the
     
* current thread becomes disabled for thread scheduling
     
* purposes and lies dormant until one of two things happens:
     
*
     
* <ul>
     
*
     
* <li>The lock is acquired by the current thread; or
     
*
     
* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
     
* current thread.
     
*
     
* </ul>
     
*
     
* <p>If the lock is acquired by the current thread then the lock hold
     
* count is set to one.
     
*
     
* <p>If the current thread:
     
*
     
* <ul>
     
*
     
* <li>has its interrupted status set on entry to this method; or
     
*
     
* <li>is {@linkplain Thread#interrupt interrupted} while acquiring
     
* the lock,
     
*
     
* </ul>
     
*
     
* then {@link InterruptedException} is thrown and the current thread's
     
* interrupted status is cleared.
     
*
     
* <p>In this implementation, as this method is an explicit
     
* interruption point, preference is given to responding to the
     
* interrupt over normal or reentrant acquisition of the lock.
     
*
     
* @throws InterruptedException if the current thread is interrupted
     
*/

    
public void lockInterruptibly() throws InterruptedException {
        
sync.acquireInterruptibly(1);
    
}

    
/**
     
* Acquires the lock only if it is not held by another thread at the time
     
* of invocation.
     
*
     
* <p>Acquires the lock if it is not held by another thread and
     
* returns immediately with the value {@code true}, setting the
     
* lock hold count to one. Even when this lock has been set to use a
     
* fair ordering policy, a call to {@code tryLock()} <em>will</em>
     
* immediately acquire the lock if it is available, whether or not
     
* other threads are currently waiting for the lock.
     
* This &quot;barging&quot; behavior can be useful in certain
     
* circumstances, even though it breaks fairness. If you want to honor
     
* the fairness setting for this lock, then use
     
* {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
     
* which is almost equivalent (it also detects interruption).
     
*
     
* <p>If the current thread already holds this lock then the hold
     
* count is incremented by one and the method returns {@code true}.
     
*
     
* <p>If the lock is held by another thread then this method will return
     
* immediately with the value {@code false}.
     
*
     
* @return {@code true} if the lock was free and was acquired by the
     
*
         
current thread, or the lock was already held by the current
     
*
         
thread; and {@code false} otherwise
     
*/

    
public boolean tryLock() {
        
return sync.nonfairTryAcquire(1);
    
}

    
/**
     
* Acquires the lock if it is not held by another thread within the given
     
* waiting time and the current thread has not been
     
* {@linkplain Thread#interrupt interrupted}.
     
*
     
* <p>Acquires the lock if it is not held by another thread and returns
     
* immediately with the value {@code true}, setting the lock hold count
     
* to one. If this lock has been set to use a fair ordering policy then
     
* an available lock <em>will not</em> be acquired if any other threads
     
* are waiting for the lock. This is in contrast to the
 

     
* 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.tryAcquireNanos(1, unit.toNanos(timeout));
    
}

    
/**
     
* Attempts to release this lock.
     
*
     
* <p>If the current thread is the holder of this lock then the hold
     
* count is decremented.
  
If the hold count is now zero then the lock
     
* is released.
  
If the current thread is not the holder of this
     
* lock then {@link IllegalMonitorStateException} is thrown.
     
*
     
* @throws IllegalMonitorStateException if the current thread does not
     
*
         
hold this lock
     
*/

    
public void unlock() {
        
sync.release(1);
    
}

    
/**
     
* Returns a {@link Condition} instance for use with this
     
* {@link Lock} instance.
     
*
     
* <p>The returned {@link Condition} instance supports the same
     
* usages as do the {@link Object} monitor methods ({@link
     
* Object#wait() wait}, {@link Object#notify notify}, and {@link
     
* Object#notifyAll notifyAll}) when used with the built-in
     
* monitor lock.
     
*
     
* <ul>
     
*
     
* <li>If this lock is not held when any of the {@link Condition}
     
* {@linkplain Condition#await() waiting} or {@linkplain
     
* Condition#signal signalling} methods are called, then an {@link
     
* IllegalMonitorStateException} is thrown.
     
*
     
* <li>When the condition {@linkplain Condition#await() waiting}
     
* methods are called the lock is released and, before they
     
* return, the lock is reacquired and the lock hold count restored
     
* to what it was when the method was called.
     
*
     
* <li>If a thread is {@linkplain Thread#interrupt interrupted}
     
* while waiting then the wait will terminate, an {@link
     
* InterruptedException} will be thrown, and the thread's
     
* interrupted status will be cleared.
     
*
     
* <li> Waiting threads are signalled in FIFO order.
     
*
     
* <li>The ordering of lock reacquisition for threads returning
     
* from waiting methods is the same as for threads initially
     
* acquiring the lock, which is in the default case not specified,
     
* but for <em>fair</em> locks favors those threads that have been
     
* waiting the longest.
     
*
     
* </ul>
     
*
     
* @return the Condition object
     
*/

    
public Condition newCondition() {
        
return sync.newCondition();
    
}

    
/**
     
* Queries the number of holds on this lock by the current thread.
     
*
     
* <p>A thread has a hold on a lock for each lock action that is not
     
* matched by an unlock action.
     
*
     
* <p>The hold count information is typically only used for testing and
     
* debugging purposes. For example, if a certain section of code should
     
* not be entered with the lock already held then we can assert that
     
* fact:
     
*
     
*
  
<pre> {@code
     
* class X {
     
*
   
ReentrantLock lock = new ReentrantLock();
     
*
   
// ...
     
*
   
public void m() {
     
*assert lock.getHoldCount() == 0;
     
*lock.lock();
     
*try {
     
*
       
// ... method body
     
*} finally {
     
*
       
lock.unlock();
     
*}
     
*
   
}
     
* }}</pre>
     
*
     
* @return the number of holds on this lock by the current thread,
     
*
         
or zero if this lock is not held by the current thread
     
*/

    
public int getHoldCount() {
        
return sync.getHoldCount();
    
}

    
/**
     
* Queries if this lock is held by the current thread.
     
*
     
* <p>Analogous to the {@link Thread#holdsLock(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 {
     
*
   
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 {
     
*
   
ReentrantLock lock = new ReentrantLock();
     
*
   
// ...
     
*
     
*
   
public void m() {
     
*
       
assert !lock.isHeldByCurrentThread();
     
*
       
lock.lock();
     
*
       
try {
     
*
           
// ... method body
     
*
       
} finally {
     
*
           
lock.unlock();
     
*
       
}
     
*
   
}
     
* }}</pre>
     
*
     
* @return {@code true} if current thread holds this lock and
     
*
         
{@code false} otherwise
     
*/

    
public boolean isHeldByCurrentThread() {
        
return sync.isHeldExclusively();
    
}

    
/**
     
* Queries if this lock is held by any thread. This method is
     
* designed for use in monitoring of the system state,
     
* not for synchronization control.
     
*
     
* @return {@code true} if any thread holds this lock and
     
*
         
{@code false} otherwise
     
*/

    
public boolean isLocked() {
        
return sync.isLocked();
    
}

    
/**
     
* Returns {@code true} if this lock has fairness set true.
     
*
     
* @return {@code true} if this lock has fairness set true
     
*/

    
public final boolean isFair() {
        
return sync instanceof FairSync;
    
}

    
/**
     
* Returns the thread that currently owns this lock, or
     
* {@code null} if not owned. When this method is called by a
     
* thread that is not the owner, the return value reflects a
     
* best-effort approximation of current lock status. For example,
     
* the owner may be momentarily {@code null} even if there are
     
* threads trying to acquire the lock but have not yet done so.
     
* This method is designed to facilitate construction of
     
* subclasses that provide more extensive lock monitoring
     
* facilities.
     
*
     
* @return the owner, or {@code null} if not owned
     
*/

    
protected Thread getOwner() {
        
return sync.getOwner();
    
}

    
/**
     
* Queries whether any threads are waiting to acquire this lock. Note that
     
* because cancellations may occur at any time, a {@code true}
     
* return does not guarantee that any other thread will ever
     
* acquire this lock.
  
This method is designed primarily for use in
     
* monitoring of the system state.
     
*
     
* @return {@code true} if there may be other threads waiting to
     
*
         
acquire the lock
     
*/

    
public final boolean hasQueuedThreads() {
        
return sync.hasQueuedThreads();
    
}

    
/**
     
* Queries whether the given thread is waiting to acquire this
     
* lock. Note that because cancellations may occur at any time, a
     
* {@code true} return does not guarantee that this thread
     
* will ever acquire this lock.
  
This method is designed primarily for use
     
* in monitoring of the system state.
     
*
     
* @param thread the thread
     
* @return {@code true} if the given thread is queued waiting for this lock
     
* @throws NullPointerException if the thread is null
     
*/

    
public final boolean hasQueuedThread(Thread thread) {
        
return sync.isQueued(thread);
    
}

    
/**
     
* Returns an estimate of the number of threads waiting to
     
* acquire this lock.
  
The value is only an estimate because the number of
     
* threads may change dynamically while this method traverses
     
* internal data structures.
  
This method is designed for use in
     
* monitoring of the system state, not for synchronization
     
* control.
     
*
     
* @return the estimated number of threads waiting for this lock
     
*/

    
public final int getQueueLength() {
        
return sync.getQueueLength();
    
}

    
/**
     
* Returns a collection containing threads that may be waiting to
     
* acquire this lock.
  
Because the actual set of threads may change
     
* dynamically while constructing this result, the returned
     
* collection is only a best-effort estimate.
  
The elements of the
     
* returned collection are in no particular order.
  
This method is
     
* designed to facilitate construction of subclasses that provide
     
* more extensive monitoring facilities.
     
*
     
* @return the collection of threads
     
*/

    
protected Collection<Thread> getQueuedThreads() {
        
return sync.getQueuedThreads();
    
}

    
/**
     
* Queries whether any threads are waiting on the given condition
     
* associated with this lock. Note that because timeouts and
     
* interrupts may occur at any time, a {@code true} return does
     
* not guarantee that a future {@code signal} will awaken any
     
* threads.
  
This method is designed primarily for use in
     
* monitoring of the system state.
     
*
     
* @param condition the condition
     
* @return {@code true} if there are any waiting threads
     
* @throws IllegalMonitorStateException if this lock is not held
     
* @throws IllegalArgumentException if the given condition is
     
*
         
not associated with this lock
     
* @throws NullPointerException if the condition is null
     
*/

    
public boolean hasWaiters(Condition condition) {
        
if (condition == null)
            
throw new NullPointerException();
        
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            
throw new IllegalArgumentException("not owner");
        
return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
    
}

    
/**
     
* Returns an estimate of the number of threads waiting on the
     
* given condition associated with this lock. Note that because
     
* timeouts and interrupts may occur at any time, the estimate
     
* serves only as an upper bound on the actual number of waiters.
     
* This method is designed for use in monitoring of the system
     
* state, not for synchronization control.
     
*
     
* @param condition the condition
     
* @return the estimated number of waiting threads
     
* @throws IllegalMonitorStateException if this lock is not held
     
* @throws IllegalArgumentException if the given condition is
     
*
         
not associated with this lock
     
* @throws NullPointerException if the condition is null
     
*/

    
public int getWaitQueueLength(Condition condition) {
        
if (condition == null)
            
throw new NullPointerException();
        
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            
throw new IllegalArgumentException("not owner");
        
return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
    
}

    
/**
     
* Returns a collection containing those threads that may be
     
* waiting on the given condition associated with this lock.
     
* Because the actual set of threads may change dynamically while
     
* constructing this result, the returned collection is only a
     
* best-effort estimate. The elements of the returned collection
     
* are in no particular order.
  
This method is designed to
     
* facilitate construction of subclasses that provide more
     
* extensive condition monitoring facilities.
     
*
     
* @param condition the condition
     
* @return the collection of threads
     
* @throws IllegalMonitorStateException if this lock is not held
     
* @throws IllegalArgumentException if the given condition is
     
*
         
not associated with this lock
     
* @throws NullPointerException if the condition is null
     
*/

    
protected Collection<Thread> getWaitingThreads(Condition condition) {
        
if (condition == null)
            
throw new NullPointerException();
        
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            
throw new IllegalArgumentException("not owner");
        
return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
    
}

    
/**
     
* Returns a string identifying this lock, as well as its lock state.
     
* The state, in brackets, includes either the String {@code "Unlocked"}
     
* or the String {@code "Locked by"} followed by the
     
* {@linkplain Thread#getName name} of the owning thread.
     
*
     
* @return a string identifying this lock, as well as its lock state
     
*/

    
public String toString() {
        
Thread o = sync.getOwner();
        
return super.toString() + ((o == null) ?
                                   
"[Unlocked]" :
                                   
"[Locked by thread " + o.getName() + "]");
    
}
}