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	/*
	* 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. tryAcquire is implemented in
	* subclasses, but both need nonfair try for trylock method.
	*/
	@ReservedStackAccess
	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;
	}

	@ReservedStackAccess
	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;
	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;
	/**
	* Fair version of tryAcquire. Don't grant access unless
	* recursive call or no waiters or is first.
	*/
	@ReservedStackAccess
	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.acquire(1);
	}

	/**
	* Acquires the lock unless the current thread is
	* {@linkplain Thread#interrupt interrupted}.
	*
	* <p>Acquires the lock if it is not held by another thread and returns
	* immediately, setting the lock hold count to one.
	*
	* <p>If the current thread already holds this lock then the hold count
	* is incremented by one and the method returns immediately.
	*
	* <p>If the lock is held by another thread then the
	* current thread becomes disabled for thread scheduling
	* purposes and lies dormant until one of two things happens:
	*
	* <ul>
	*
	* <li>The lock is acquired by the current thread; or
	*
	* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	* current thread.
	*
	* </ul>
	*
	* <p>If the lock is acquired by the current thread then the lock hold
	* count is set to one.
	*
	* <p>If the current thread:
	*
	* <ul>
	*
	* <li>has its interrupted status set on entry to this method; or
	*
	* <li>is {@linkplain Thread#interrupt interrupted} while acquiring
	* the lock,
	*
	* </ul>
	*
	* then {@link InterruptedException} is thrown and the current thread's
	* interrupted status is cleared.
	*
	* <p>In this implementation, as this method is an explicit
	* interruption point, preference is given to responding to the
	* interrupt over normal or reentrant acquisition of the lock.
	*
	* @throws InterruptedException if the current thread is interrupted
	*/
	public void lockInterruptibly() throws InterruptedException {
	sync.acquireInterruptibly(1);
	}

	/**
	* Acquires the lock only if it is not held by another thread at the time
	* of invocation.
	*
	* <p>Acquires the lock if it is not held by another thread and
	* returns immediately with the value {@code true}, setting the
	* lock hold count to one. Even when this lock has been set to use a
	* fair ordering policy, a call to {@code tryLock()} <em>will</em>
	* immediately acquire the lock if it is available, whether or not
	* other threads are currently waiting for the lock.
	* This "barging" behavior can be useful in certain
	* circumstances, even though it breaks fairness. If you want to honor
	* the fairness setting for this lock, then use
	* {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS)}
	* which is almost equivalent (it also detects interruption).
	*
	* <p>If the current thread already holds this lock then the hold
	* count is incremented by one and the method returns {@code true}.
	*
	* <p>If the lock is held by another thread then this method will return
	* immediately with the value {@code false}.
	*
	* @return {@code true} if the lock was free and was acquired by the
	* current thread, or the lock was already held by the current
	* thread; and {@code false} otherwise
	*/
	public boolean tryLock() {
	return sync.nonfairTryAcquire(1);
	}

	/**
	* Acquires the lock if it is not held by another thread within the given
	* waiting time and the current thread has not been
	* {@linkplain Thread#interrupt interrupted}.
	*
	* <p>Acquires the lock if it is not held by another thread and returns
	* immediately with the value {@code true}, setting the lock hold count
	* to one. If this lock has been set to use a fair ordering policy then
	* an available lock <em>will not</em> be acquired if any other threads
	* are waiting for the lock. This is in contrast to the {@link #tryLock()}
	* method. If you want a timed {@code tryLock} that does permit barging on
	* a fair lock then combine the timed and un-timed forms together:
	*
	* <pre> {@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 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() + "]");
	}
	}

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