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/* * @(#)ScheduledExecutorService.java 1.6 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.concurrent; import java.util.concurrent.atomic.*; import java.util.*; /** * An {@link ExecutorService} that can schedule commands to run after a given * delay, or to execute periodically. * * <p> The <tt>schedule</tt> methods create tasks with various delays * and return a task object that can be used to cancel or check * execution. The <tt>scheduleAtFixedRate</tt> and * <tt>scheduleWithFixedDelay</tt> methods create and execute tasks * that run periodically until cancelled. * * <p> Commands submitted using the {@link Executor#execute} and * {@link ExecutorService} <tt>submit</tt> methods are scheduled with * a requested delay of zero. Zero and negative delays (but not * periods) are also allowed in <tt>schedule</tt> methods, and are * treated as requests for immediate execution. * * <p>All <tt>schedule</tt> 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 <tt>date</tt>, you can use: <tt>schedule(task, * date.getTime() - System.currentTimeMillis(), * TimeUnit.MILLISECONDS)</tt>. Beware however that expiration of a * relative delay need not coincide with the current <tt>Date</tt> at * which the task is enabled due to network time synchronization * protocols, clock drift, or other factors. * * 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> * 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 <tt>get()</tt> method will return * <tt>null</tt> 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 * @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 * <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then * <tt>initialDelay + 2 * period</tt>, 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 <tt>get()</tt> 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 <tt>get()</tt> 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); }