Java example source code file (ScheduledExecutorService.java)

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Java - Java tags/keywords

executorservice, scheduledexecutorservice, scheduledfuture, timeunit

The ScheduledExecutorService.java Java example source code

/*
 * 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 relative 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
 *
 * 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() {
 *     final Runnable beeper = new Runnable() {
 *       public void run() { System.out.println("beep"); }
 *     };
 *     final ScheduledFuture<?> beeperHandle =
 *       scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
 *     scheduler.schedule(new Runnable() {
 *       public void run() { beeperHandle.cancel(true); }
 *     }, 60 * 60, SECONDS);
 *   }
 * }}</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 schedule(Callable 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.
     * If any execution of the task
     * encounters an exception, subsequent executions are suppressed.
     * Otherwise, the task will only terminate via cancellation or
     * termination of the executor.  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 task, and whose {@code get()} method will throw an
     *         exception upon cancellation
     * @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.  If any execution of the task
     * encounters an exception, subsequent executions are suppressed.
     * Otherwise, the task will only terminate via cancellation or
     * termination of the executor.
     *
     * @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 task, and whose {@code get()} method will throw an
     *         exception upon cancellation
     * @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);

}