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/*

 * 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/licenses/publicdomain

 */

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);

}