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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;

	/**
	* An {@link ExecutorService} that can schedule commands to run after a given
	* delay, or to execute periodically.
	*
	* <p>The {@code schedule} methods create tasks with various delays
	* and return a task object that can be used to cancel or check
	* execution. The {@code scheduleAtFixedRate} and
	* {@code scheduleWithFixedDelay} methods create and execute tasks
	* that run periodically until cancelled.
	*
	* <p>Commands submitted using the {@link Executor#execute(Runnable)}
	* and {@link ExecutorService} {@code submit} methods are scheduled
	* with a requested delay of zero. Zero and negative delays (but not
	* periods) are also allowed in {@code schedule} methods, and are
	* treated as requests for immediate execution.
	*
	* <p>All {@code schedule} methods accept <em>relative</em> delays and
	* periods as arguments, not absolute times or dates. It is a simple
	* matter to transform an absolute time represented as a {@link
	* java.util.Date} to the required form. For example, to schedule at
	* a certain future {@code date}, you can use: {@code schedule(task,
	* date.getTime() - System.currentTimeMillis(),
	* TimeUnit.MILLISECONDS)}. Beware however that expiration of a
	* relative delay need not coincide with the current {@code Date} at
	* which the task is enabled due to network time synchronization
	* protocols, clock drift, or other factors.
	*
	* <p>The {@link Executors} class provides convenient factory methods for
	* the ScheduledExecutorService implementations provided in this package.
	*
	* <h2>Usage Example</h2>
	*
	* Here is a class with a method that sets up a ScheduledExecutorService
	* to beep every ten seconds for an hour:
	*
	* <pre> {@code
	* import static java.util.concurrent.TimeUnit.*;
	* class BeeperControl {
	* private final ScheduledExecutorService scheduler =
	* Executors.newScheduledThreadPool(1);
	*
	* public void beepForAnHour() {
	* Runnable beeper = () -> System.out.println("beep");
	* ScheduledFuture<?> beeperHandle =
	* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
	* Runnable canceller = () -> beeperHandle.cancel(false);
	* scheduler.schedule(canceller, 1, HOURS);
	* }
	* }}</pre>
	*
	* @since 1.5
	* @author Doug Lea
	*/
	public interface ScheduledExecutorService extends ExecutorService {

	/**
	* Submits a one-shot task that becomes enabled after the given delay.
	*
	* @param command the task to execute
	* @param delay the time from now to delay execution
	* @param unit the time unit of the delay parameter
	* @return a ScheduledFuture representing pending completion of
	* the task and whose {@code get()} method will return
	* {@code null} upon completion
	* @throws RejectedExecutionException if the task cannot be
	* scheduled for execution
	* @throws NullPointerException if command or unit is null
	*/
	public ScheduledFuture<?> schedule(Runnable command,
	long delay, TimeUnit unit);

	/**
	* Submits a value-returning one-shot task that becomes enabled
	* after the given delay.
	*
	* @param callable the function to execute
	* @param delay the time from now to delay execution
	* @param unit the time unit of the delay parameter
	* @param <V> the type of the callable's result
	* @return a ScheduledFuture that can be used to extract result or cancel
	* @throws RejectedExecutionException if the task cannot be
	* scheduled for execution
	* @throws NullPointerException if callable or unit is null
	*/
	public <V> ScheduledFuture<V> schedule(Callable<V> callable,
	long delay, TimeUnit unit);

	/**
	* Submits a periodic action that becomes enabled first after the
	* given initial delay, and subsequently with the given period;
	* that is, executions will commence after
	* {@code initialDelay}, then {@code initialDelay + period}, then
	* {@code initialDelay + 2 * period}, and so on.
	*
	* <p>The sequence of task executions continues indefinitely until
	* one of the following exceptional completions occur:
	* <ul>
	* <li>The task is {@linkplain Future#cancel explicitly cancelled}
	* via the returned future.
	* <li>The executor terminates, also resulting in task cancellation.
	* <li>An execution of the task throws an exception. In this case
	* calling {@link Future#get() get} on the returned future will throw
	* {@link ExecutionException}, holding the exception as its cause.
	* </ul>
	* Subsequent executions are suppressed. Subsequent calls to
	* {@link Future#isDone isDone()} on the returned future will
	* return {@code true}.
	*
	* <p>If any execution of this task takes longer than its period, then
	* subsequent executions may start late, but will not concurrently
	* execute.
	*
	* @param command the task to execute
	* @param initialDelay the time to delay first execution
	* @param period the period between successive executions
	* @param unit the time unit of the initialDelay and period parameters
	* @return a ScheduledFuture representing pending completion of
	* the series of repeated tasks. The future's {@link
	* Future#get() get()} method will never return normally,
	* and will throw an exception upon task cancellation or
	* abnormal termination of a task execution.
	* @throws RejectedExecutionException if the task cannot be
	* scheduled for execution
	* @throws NullPointerException if command or unit is null
	* @throws IllegalArgumentException if period less than or equal to zero
	*/
	public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
	long initialDelay,
	long period,
	TimeUnit unit);

	/**
	* Submits a periodic action that becomes enabled first after the
	* given initial delay, and subsequently with the given delay
	* between the termination of one execution and the commencement of
	* the next.
	*
	* <p>The sequence of task executions continues indefinitely until
	* one of the following exceptional completions occur:
	* <ul>
	* <li>The task is {@linkplain Future#cancel explicitly cancelled}
	* via the returned future.
	* <li>The executor terminates, also resulting in task cancellation.
	* <li>An execution of the task throws an exception. In this case
	* calling {@link Future#get() get} on the returned future will throw
	* {@link ExecutionException}, holding the exception as its cause.
	* </ul>
	* Subsequent executions are suppressed. Subsequent calls to
	* {@link Future#isDone isDone()} on the returned future will
	* return {@code true}.
	*
	* @param command the task to execute
	* @param initialDelay the time to delay first execution
	* @param delay the delay between the termination of one
	* execution and the commencement of the next
	* @param unit the time unit of the initialDelay and delay parameters
	* @return a ScheduledFuture representing pending completion of
	* the series of repeated tasks. The future's {@link
	* Future#get() get()} method will never return normally,
	* and will throw an exception upon task cancellation or
	* abnormal termination of a task execution.
	* @throws RejectedExecutionException if the task cannot be
	* scheduled for execution
	* @throws NullPointerException if command or unit is null
	* @throws IllegalArgumentException if delay less than or equal to zero
	*/
	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
	long initialDelay,
	long delay,
	TimeUnit unit);

	}

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