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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.Date;
	import java.util.concurrent.TimeUnit;

	/**
	* {@code Condition} factors out the {@code Object} monitor
	* methods ({@link Object#wait() wait}, {@link Object#notify notify}
	* and {@link Object#notifyAll notifyAll}) into distinct objects to
	* give the effect of having multiple wait-sets per object, by
	* combining them with the use of arbitrary {@link Lock} implementations.
	* Where a {@code Lock} replaces the use of {@code synchronized} methods
	* and statements, a {@code Condition} replaces the use of the Object
	* monitor methods.
	*
	* <p>Conditions (also known as <em>condition queues</em> or
	* <em>condition variables</em>) provide a means for one thread to
	* suspend execution (to "wait") until notified by another
	* thread that some state condition may now be true. Because access
	* to this shared state information occurs in different threads, it
	* must be protected, so a lock of some form is associated with the
	* condition. The key property that waiting for a condition provides
	* is that it <em>atomically</em> releases the associated lock and
	* suspends the current thread, just like {@code Object.wait}.
	*
	* <p>A {@code Condition} instance is intrinsically bound to a lock.
	* To obtain a {@code Condition} instance for a particular {@link Lock}
	* instance use its {@link Lock#newCondition newCondition()} method.
	*
	* <p>As an example, suppose we have a bounded buffer which supports
	* {@code put} and {@code take} methods. If a
	* {@code take} is attempted on an empty buffer, then the thread will block
	* until an item becomes available; if a {@code put} is attempted on a
	* full buffer, then the thread will block until a space becomes available.
	* We would like to keep waiting {@code put} threads and {@code take}
	* threads in separate wait-sets so that we can use the optimization of
	* only notifying a single thread at a time when items or spaces become
	* available in the buffer. This can be achieved using two
	* {@link Condition} instances.
	* <pre>
	* class BoundedBuffer<E> {
	* <b>final Lock lock = new ReentrantLock();</b>
	* final Condition notFull = <b>lock.newCondition(); </b>
	* final Condition notEmpty = <b>lock.newCondition(); </b>
	*
	* final Object[] items = new Object[100];
	* int putptr, takeptr, count;
	*
	* public void put(E x) throws InterruptedException {
	* <b>lock.lock();
	* try {</b>
	* while (count == items.length)
	* <b>notFull.await();</b>
	* items[putptr] = x;
	* if (++putptr == items.length) putptr = 0;
	* ++count;
	* <b>notEmpty.signal();</b>
	* <b>} finally {
	* lock.unlock();
	* }</b>
	* }
	*
	* public E take() throws InterruptedException {
	* <b>lock.lock();
	* try {</b>
	* while (count == 0)
	* <b>notEmpty.await();</b>
	* E x = (E) items[takeptr];
	* if (++takeptr == items.length) takeptr = 0;
	* --count;
	* <b>notFull.signal();</b>
	* return x;
	* <b>} finally {
	* lock.unlock();
	* }</b>
	* }
	* }
	* </pre>
	*
	* (The {@link java.util.concurrent.ArrayBlockingQueue} class provides
	* this functionality, so there is no reason to implement this
	* sample usage class.)
	*
	* <p>A {@code Condition} implementation can provide behavior and semantics
	* that is
	* different from that of the {@code Object} monitor methods, such as
	* guaranteed ordering for notifications, or not requiring a lock to be held
	* when performing notifications.
	* If an implementation provides such specialized semantics then the
	* implementation must document those semantics.
	*
	* <p>Note that {@code Condition} instances are just normal objects and can
	* themselves be used as the target in a {@code synchronized} statement,
	* and can have their own monitor {@link Object#wait wait} and
	* {@link Object#notify notify} methods invoked.
	* Acquiring the monitor lock of a {@code Condition} instance, or using its
	* monitor methods, has no specified relationship with acquiring the
	* {@link Lock} associated with that {@code Condition} or the use of its
	* {@linkplain #await waiting} and {@linkplain #signal signalling} methods.
	* It is recommended that to avoid confusion you never use {@code Condition}
	* instances in this way, except perhaps within their own implementation.
	*
	* <p>Except where noted, passing a {@code null} value for any parameter
	* will result in a {@link NullPointerException} being thrown.
	*
	* <h2>Implementation Considerations</h2>
	*
	* <p>When waiting upon a {@code Condition}, a "<em>spurious
	* wakeup</em>" is permitted to occur, in
	* general, as a concession to the underlying platform semantics.
	* This has little practical impact on most application programs as a
	* {@code Condition} should always be waited upon in a loop, testing
	* the state predicate that is being waited for. An implementation is
	* free to remove the possibility of spurious wakeups but it is
	* recommended that applications programmers always assume that they can
	* occur and so always wait in a loop.
	*
	* <p>The three forms of condition waiting
	* (interruptible, non-interruptible, and timed) may differ in their ease of
	* implementation on some platforms and in their performance characteristics.
	* In particular, it may be difficult to provide these features and maintain
	* specific semantics such as ordering guarantees.
	* Further, the ability to interrupt the actual suspension of the thread may
	* not always be feasible to implement on all platforms.
	*
	* <p>Consequently, an implementation is not required to define exactly the
	* same guarantees or semantics for all three forms of waiting, nor is it
	* required to support interruption of the actual suspension of the thread.
	*
	* <p>An implementation is required to
	* clearly document the semantics and guarantees provided by each of the
	* waiting methods, and when an implementation does support interruption of
	* thread suspension then it must obey the interruption semantics as defined
	* in this interface.
	*
	* <p>As interruption generally implies cancellation, and checks for
	* interruption are often infrequent, an implementation can favor responding
	* to an interrupt over normal method return. This is true even if it can be
	* shown that the interrupt occurred after another action that may have
	* unblocked the thread. An implementation should document this behavior.
	*
	* @since 1.5
	* @author Doug Lea
	*/
	public interface Condition {

	/**
	* Causes the current thread to wait until it is signalled or
	* {@linkplain Thread#interrupt interrupted}.
	*
	* <p>The lock associated with this {@code Condition} is atomically
	* released and the current thread becomes disabled for thread scheduling
	* purposes and lies dormant until <em>one</em> of four things happens:
	* <ul>
	* <li>Some other thread invokes the {@link #signal} method for this
	* {@code Condition} and the current thread happens to be chosen as the
	* thread to be awakened; or
	* <li>Some other thread invokes the {@link #signalAll} method for this
	* {@code Condition}; or
	* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	* current thread, and interruption of thread suspension is supported; or
	* <li>A "<em>spurious wakeup</em>" occurs.
	* </ul>
	*
	* <p>In all cases, before this method can return the current thread must
	* re-acquire the lock associated with this condition. When the
	* thread returns it is <em>guaranteed</em> to hold this lock.
	*
	* <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 waiting
	* and interruption of thread suspension is supported,
	* </ul>
	* then {@link InterruptedException} is thrown and the current thread's
	* interrupted status is cleared. It is not specified, in the first
	* case, whether or not the test for interruption occurs before the lock
	* is released.
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>The current thread is assumed to hold the lock associated with this
	* {@code Condition} when this method is called.
	* It is up to the implementation to determine if this is
	* the case and if not, how to respond. Typically, an exception will be
	* thrown (such as {@link IllegalMonitorStateException}) and the
	* implementation must document that fact.
	*
	* <p>An implementation can favor responding to an interrupt over normal
	* method return in response to a signal. In that case the implementation
	* must ensure that the signal is redirected to another waiting thread, if
	* there is one.
	*
	* @throws InterruptedException if the current thread is interrupted
	* (and interruption of thread suspension is supported)
	*/
	void await() throws InterruptedException;

	/**
	* Causes the current thread to wait until it is signalled.
	*
	* <p>The lock associated with this condition is atomically
	* released and the current thread becomes disabled for thread scheduling
	* purposes and lies dormant until <em>one</em> of three things happens:
	* <ul>
	* <li>Some other thread invokes the {@link #signal} method for this
	* {@code Condition} and the current thread happens to be chosen as the
	* thread to be awakened; or
	* <li>Some other thread invokes the {@link #signalAll} method for this
	* {@code Condition}; or
	* <li>A "<em>spurious wakeup</em>" occurs.
	* </ul>
	*
	* <p>In all cases, before this method can return the current thread must
	* re-acquire the lock associated with this condition. When the
	* thread returns it is <em>guaranteed</em> to hold this lock.
	*
	* <p>If the current thread's interrupted status is set when it enters
	* this method, or it is {@linkplain Thread#interrupt interrupted}
	* while waiting, it will continue to wait until signalled. When it finally
	* returns from this method its interrupted status will still
	* be set.
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>The current thread is assumed to hold the lock associated with this
	* {@code Condition} when this method is called.
	* It is up to the implementation to determine if this is
	* the case and if not, how to respond. Typically, an exception will be
	* thrown (such as {@link IllegalMonitorStateException}) and the
	* implementation must document that fact.
	*/
	void awaitUninterruptibly();

	/**
	* Causes the current thread to wait until it is signalled or interrupted,
	* or the specified waiting time elapses.
	*
	* <p>The lock associated with this condition is atomically
	* released and the current thread becomes disabled for thread scheduling
	* purposes and lies dormant until <em>one</em> of five things happens:
	* <ul>
	* <li>Some other thread invokes the {@link #signal} method for this
	* {@code Condition} and the current thread happens to be chosen as the
	* thread to be awakened; or
	* <li>Some other thread invokes the {@link #signalAll} method for this
	* {@code Condition}; or
	* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	* current thread, and interruption of thread suspension is supported; or
	* <li>The specified waiting time elapses; or
	* <li>A "<em>spurious wakeup</em>" occurs.
	* </ul>
	*
	* <p>In all cases, before this method can return the current thread must
	* re-acquire the lock associated with this condition. When the
	* thread returns it is <em>guaranteed</em> to hold this lock.
	*
	* <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 waiting
	* and interruption of thread suspension is supported,
	* </ul>
	* then {@link InterruptedException} is thrown and the current thread's
	* interrupted status is cleared. It is not specified, in the first
	* case, whether or not the test for interruption occurs before the lock
	* is released.
	*
	* <p>The method returns an estimate of the number of nanoseconds
	* remaining to wait given the supplied {@code nanosTimeout}
	* value upon return, or a value less than or equal to zero if it
	* timed out. This value can be used to determine whether and how
	* long to re-wait in cases where the wait returns but an awaited
	* condition still does not hold. Typical uses of this method take
	* the following form:
	*
	* <pre> {@code
	* boolean aMethod(long timeout, TimeUnit unit)
	* throws InterruptedException {
	* long nanosRemaining = unit.toNanos(timeout);
	* lock.lock();
	* try {
	* while (!conditionBeingWaitedFor()) {
	* if (nanosRemaining <= 0L)
	* return false;
	* nanosRemaining = theCondition.awaitNanos(nanosRemaining);
	* }
	* // ...
	* return true;
	* } finally {
	* lock.unlock();
	* }
	* }}</pre>
	*
	* <p>Design note: This method requires a nanosecond argument so
	* as to avoid truncation errors in reporting remaining times.
	* Such precision loss would make it difficult for programmers to
	* ensure that total waiting times are not systematically shorter
	* than specified when re-waits occur.
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>The current thread is assumed to hold the lock associated with this
	* {@code Condition} when this method is called.
	* It is up to the implementation to determine if this is
	* the case and if not, how to respond. Typically, an exception will be
	* thrown (such as {@link IllegalMonitorStateException}) and the
	* implementation must document that fact.
	*
	* <p>An implementation can favor responding to an interrupt over normal
	* method return in response to a signal, or over indicating the elapse
	* of the specified waiting time. In either case the implementation
	* must ensure that the signal is redirected to another waiting thread, if
	* there is one.
	*
	* @param nanosTimeout the maximum time to wait, in nanoseconds
	* @return an estimate of the {@code nanosTimeout} value minus
	* the time spent waiting upon return from this method.
	* A positive value may be used as the argument to a
	* subsequent call to this method to finish waiting out
	* the desired time. A value less than or equal to zero
	* indicates that no time remains.
	* @throws InterruptedException if the current thread is interrupted
	* (and interruption of thread suspension is supported)
	*/
	long awaitNanos(long nanosTimeout) throws InterruptedException;

	/**
	* Causes the current thread to wait until it is signalled or interrupted,
	* or the specified waiting time elapses. This method is behaviorally
	* equivalent to:
	* <pre> {@code awaitNanos(unit.toNanos(time)) > 0}</pre>
	*
	* @param time the maximum time to wait
	* @param unit the time unit of the {@code time} argument
	* @return {@code false} if the waiting time detectably elapsed
	* before return from the method, else {@code true}
	* @throws InterruptedException if the current thread is interrupted
	* (and interruption of thread suspension is supported)
	*/
	boolean await(long time, TimeUnit unit) throws InterruptedException;

	/**
	* Causes the current thread to wait until it is signalled or interrupted,
	* or the specified deadline elapses.
	*
	* <p>The lock associated with this condition is atomically
	* released and the current thread becomes disabled for thread scheduling
	* purposes and lies dormant until <em>one</em> of five things happens:
	* <ul>
	* <li>Some other thread invokes the {@link #signal} method for this
	* {@code Condition} and the current thread happens to be chosen as the
	* thread to be awakened; or
	* <li>Some other thread invokes the {@link #signalAll} method for this
	* {@code Condition}; or
	* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	* current thread, and interruption of thread suspension is supported; or
	* <li>The specified deadline elapses; or
	* <li>A "<em>spurious wakeup</em>" occurs.
	* </ul>
	*
	* <p>In all cases, before this method can return the current thread must
	* re-acquire the lock associated with this condition. When the
	* thread returns it is <em>guaranteed</em> to hold this lock.
	*
	* <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 waiting
	* and interruption of thread suspension is supported,
	* </ul>
	* then {@link InterruptedException} is thrown and the current thread's
	* interrupted status is cleared. It is not specified, in the first
	* case, whether or not the test for interruption occurs before the lock
	* is released.
	*
	* <p>The return value indicates whether the deadline has elapsed,
	* which can be used as follows:
	* <pre> {@code
	* boolean aMethod(Date deadline)
	* throws InterruptedException {
	* boolean stillWaiting = true;
	* lock.lock();
	* try {
	* while (!conditionBeingWaitedFor()) {
	* if (!stillWaiting)
	* return false;
	* stillWaiting = theCondition.awaitUntil(deadline);
	* }
	* // ...
	* return true;
	* } finally {
	* lock.unlock();
	* }
	* }}</pre>
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>The current thread is assumed to hold the lock associated with this
	* {@code Condition} when this method is called.
	* It is up to the implementation to determine if this is
	* the case and if not, how to respond. Typically, an exception will be
	* thrown (such as {@link IllegalMonitorStateException}) and the
	* implementation must document that fact.
	*
	* <p>An implementation can favor responding to an interrupt over normal
	* method return in response to a signal, or over indicating the passing
	* of the specified deadline. In either case the implementation
	* must ensure that the signal is redirected to another waiting thread, if
	* there is one.
	*
	* @param deadline the absolute time to wait until
	* @return {@code false} if the deadline has elapsed upon return, else
	* {@code true}
	* @throws InterruptedException if the current thread is interrupted
	* (and interruption of thread suspension is supported)
	*/
	boolean awaitUntil(Date deadline) throws InterruptedException;

	/**
	* Wakes up one waiting thread.
	*
	* <p>If any threads are waiting on this condition then one
	* is selected for waking up. That thread must then re-acquire the
	* lock before returning from {@code await}.
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>An implementation may (and typically does) require that the
	* current thread hold the lock associated with this {@code
	* Condition} when this method is called. Implementations must
	* document this precondition and any actions taken if the lock is
	* not held. Typically, an exception such as {@link
	* IllegalMonitorStateException} will be thrown.
	*/
	void signal();

	/**
	* Wakes up all waiting threads.
	*
	* <p>If any threads are waiting on this condition then they are
	* all woken up. Each thread must re-acquire the lock before it can
	* return from {@code await}.
	*
	* <p><b>Implementation Considerations</b>
	*
	* <p>An implementation may (and typically does) require that the
	* current thread hold the lock associated with this {@code
	* Condition} when this method is called. Implementations must
	* document this precondition and any actions taken if the lock is
	* not held. Typically, an exception such as {@link
	* IllegalMonitorStateException} will be thrown.
	*/
	void signalAll();
	}

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