/*

 * 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

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 */

/*

 * 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.

 *

 * <h3>Usage Example</h3>

 *

 * 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(true);

 *     scheduler.schedule(canceller, 1, HOURS);

 *   }

 * }}</pre>

 *

 * @since 1.5

 * @author Doug Lea

 */

public interface ScheduledExecutorService extends ExecutorService {

    /**

     * Creates and executes a one-shot action 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 is null

     */

    public ScheduledFuture<?> schedule(Runnable command,

                                       long delay, TimeUnit unit);

    /**

     * Creates and executes a ScheduledFuture 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 is null

     */

    public <V> ScheduledFuture<V> schedule(Callable<V> callable,

                                           long delay, TimeUnit unit);

    /**

     * Creates and executes 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}.

     * </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 is null

     * @throws IllegalArgumentException if period less than or equal to zero

     */

    public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,

                                                  long initialDelay,

                                                  long period,

                                                  TimeUnit unit);

    /**

     * Creates and executes 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}.

     * </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 is null

     * @throws IllegalArgumentException if delay less than or equal to zero

     */

    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,

                                                     long initialDelay,

                                                     long delay,

                                                     TimeUnit unit);

}