/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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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/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.
 *
 * <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> {@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);

}