/*
* 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);
}