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jeremybenn |
/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/licenses/publicdomain
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*/
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package java.util.concurrent;
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import java.util.concurrent.atomic.*;
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import java.util.*;
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/**
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* An {@link ExecutorService} that can schedule commands to run after a given
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* delay, or to execute periodically.
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*
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* <p> The <tt>schedule</tt> methods create tasks with various delays
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* and return a task object that can be used to cancel or check
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* execution. The <tt>scheduleAtFixedRate</tt> and
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* <tt>scheduleWithFixedDelay</tt> methods create and execute tasks
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* that run periodically until cancelled.
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*
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* <p> Commands submitted using the {@link Executor#execute} and
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* {@link ExecutorService} <tt>submit</tt> methods are scheduled with
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* a requested delay of zero. Zero and negative delays (but not
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* periods) are also allowed in <tt>schedule</tt> methods, and are
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* treated as requests for immediate execution.
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*
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* <p>All <tt>schedule</tt> methods accept <em>relative</em> delays and
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* periods as arguments, not absolute times or dates. It is a simple
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* matter to transform an absolute time represented as a {@link
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* java.util.Date} to the required form. For example, to schedule at
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* a certain future <tt>date</tt>, you can use: <tt>schedule(task,
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* date.getTime() - System.currentTimeMillis(),
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* TimeUnit.MILLISECONDS)</tt>. Beware however that expiration of a
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* relative delay need not coincide with the current <tt>Date</tt> at
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* which the task is enabled due to network time synchronization
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* protocols, clock drift, or other factors.
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*
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* The {@link Executors} class provides convenient factory methods for
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* the ScheduledExecutorService implementations provided in this package.
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*
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* <h3>Usage Example</h3>
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*
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* Here is a class with a method that sets up a ScheduledExecutorService
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* to beep every ten seconds for an hour:
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*
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* <pre>
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* import static java.util.concurrent.TimeUnit.*;
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* class BeeperControl {
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* private final ScheduledExecutorService scheduler =
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* Executors.newScheduledThreadPool(1);
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*
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* public void beepForAnHour() {
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* final Runnable beeper = new Runnable() {
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* public void run() { System.out.println("beep"); }
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* };
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* final ScheduledFuture<?> beeperHandle =
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* scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
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* scheduler.schedule(new Runnable() {
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* public void run() { beeperHandle.cancel(true); }
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* }, 60 * 60, SECONDS);
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* }
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* }
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* </pre>
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*
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* @since 1.5
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* @author Doug Lea
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*/
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public interface ScheduledExecutorService extends ExecutorService {
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/**
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* Creates and executes a one-shot action that becomes enabled
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* after the given delay.
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*
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* @param command the task to execute
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* @param delay the time from now to delay execution
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* @param unit the time unit of the delay parameter
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* @return a ScheduledFuture representing pending completion of
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* the task and whose <tt>get()</tt> method will return
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* <tt>null</tt> upon completion
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if command is null
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*/
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public ScheduledFuture<?> schedule(Runnable command,
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long delay, TimeUnit unit);
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/**
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* Creates and executes a ScheduledFuture that becomes enabled after the
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* given delay.
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*
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* @param callable the function to execute
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* @param delay the time from now to delay execution
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* @param unit the time unit of the delay parameter
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* @return a ScheduledFuture that can be used to extract result or cancel
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if callable is null
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*/
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public <V> ScheduledFuture<V> schedule(Callable<V> callable,
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long delay, TimeUnit unit);
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/**
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* Creates and executes a periodic action that becomes enabled first
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* after the given initial delay, and subsequently with the given
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* period; that is executions will commence after
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* <tt>initialDelay</tt> then <tt>initialDelay+period</tt>, then
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* <tt>initialDelay + 2 * period</tt>, and so on.
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* If any execution of the task
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* encounters an exception, subsequent executions are suppressed.
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* Otherwise, the task will only terminate via cancellation or
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* termination of the executor. If any execution of this task
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* takes longer than its period, then subsequent executions
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* may start late, but will not concurrently execute.
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*
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* @param command the task to execute
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* @param initialDelay the time to delay first execution
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* @param period the period between successive executions
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* @param unit the time unit of the initialDelay and period parameters
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* @return a ScheduledFuture representing pending completion of
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* the task, and whose <tt>get()</tt> method will throw an
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* exception upon cancellation
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if command is null
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* @throws IllegalArgumentException if period less than or equal to zero
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*/
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public ScheduledFuture<?> scheduleAtFixedRate(Runnable command,
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long initialDelay,
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long period,
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TimeUnit unit);
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/**
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* Creates and executes a periodic action that becomes enabled first
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* after the given initial delay, and subsequently with the
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* given delay between the termination of one execution and the
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* commencement of the next. If any execution of the task
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* encounters an exception, subsequent executions are suppressed.
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* Otherwise, the task will only terminate via cancellation or
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* termination of the executor.
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*
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* @param command the task to execute
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* @param initialDelay the time to delay first execution
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* @param delay the delay between the termination of one
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* execution and the commencement of the next
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* @param unit the time unit of the initialDelay and delay parameters
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* @return a ScheduledFuture representing pending completion of
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* the task, and whose <tt>get()</tt> method will throw an
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* exception upon cancellation
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if command is null
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* @throws IllegalArgumentException if delay less than or equal to zero
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*/
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public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
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long initialDelay,
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long delay,
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TimeUnit unit);
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}
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