Interface ScheduledExecutorService

All Superinterfaces:
AutoCloseable, Executor, ExecutorService
All Known Implementing Classes:
ForkJoinPool, ScheduledThreadPoolExecutor
public interface ScheduledExecutorService extends ExecutorService
An ExecutorService that can schedule commands to run after a given delay, or to execute periodically.

The schedule methods create tasks with various delays and return ScheduledFuture objects that can be used to cancel or check execution. When delays elapse, tasks are enabled for execution and behave in accord with other ExecutorService tasks, except that scheduleAtFixedRate and scheduleWithFixedDelay methods create and execute tasks that run periodically until cancelled.

Commands submitted using the Executor.execute(Runnable) and ExecutorService submit methods are scheduled with a requested delay of zero. Zero and negative delays (but not periods) are also allowed in schedule methods, and are treated as requests for immediate execution.

All schedule methods accept relative delays and periods as arguments, not absolute times or dates. It is a simple matter to transform an absolute time represented as a Date to the required form. For example, to schedule at a certain future date, you can use: schedule(task, date.getTime() - System.currentTimeMillis(), TimeUnit.MILLISECONDS). Beware however that expiration of a relative delay need not coincide with the current Date at which the task is enabled due to network time synchronization protocols, clock drift, or other factors.

The Executors class provides convenient factory methods for the ScheduledExecutorService implementations provided in this package.

Usage Example

Here is a class with a method that sets up a ScheduledExecutorService to beep every ten seconds for an hour: 
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);
  }
}
Since:
1.5

  • Method Summary

    Modifier and Type
    Method
    Description
    ScheduledFuture<?>
    schedule(Runnable command, long delay, TimeUnit unit)
    Submits a one-shot task that becomes enabled for execution after the given delay.
    <V> ScheduledFuture<V>
    schedule(Callable<V> callable, long delay, TimeUnit unit)
    Submits a value-returning one-shot task that becomes enabled for execution after the given delay.
    ScheduledFuture<?>
    scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
    Submits a periodic action that becomes enabled for execution first after the given initial delay, and subsequently with the given period; that is, executions will commence after initialDelay, then initialDelay + period, then initialDelay + 2 * period, and so on.
    ScheduledFuture<?>
    scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
    Submits a periodic action that becomes enabled for execution first after the given initial delay, and subsequently with the given delay between the termination of one execution and the commencement of the next.

    Methods declared in interface Executor

    execute
    Modifier and Type
    Method
    Description
    void
    execute(Runnable command)
    Executes the given command at some time in the future.

    Methods declared in interface ExecutorService

    awaitTermination, close, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminated, shutdown, shutdownNow, submit, submit, submit
    Modifier and Type
    Method
    Description
    boolean
    awaitTermination(long timeout, TimeUnit unit)
    Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
    default void
    close()
    Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
    <T> List<Future<T>>
    invokeAll(Collection<? extends Callable<T>> tasks)
    Executes the given tasks, returning a list of Futures holding their status and results when all complete.
    <T> List<Future<T>>
    invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
    Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
    <T> T
    invokeAny(Collection<? extends Callable<T>> tasks)
    Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
    <T> T
    invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
    Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
    boolean
    isShutdown()
    Returns true if this executor has been shut down.
    boolean
    isTerminated()
    Returns true if all tasks have completed following shut down.
    void
    shutdown()
    Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
    List<Runnable>
    shutdownNow()
    Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
    Future<?>
    submit(Runnable task)
    Submits a Runnable task for execution and returns a Future representing that task.
    <T> Future<T>
    submit(Runnable task, T result)
    Submits a Runnable task for execution and returns a Future representing that task.
    <T> Future<T>
    submit(Callable<T> task)
    Submits a value-returning task for execution and returns a Future representing the pending results of the task.

  • Method Details

    • schedule

      ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
      Submits a one-shot task that becomes enabled for execution after the given delay.
      Parameters:
      command - the task to execute
      delay - the time from now to delay execution
      unit - the time unit of the delay parameter
      Returns:
      a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion
      Throws:
      RejectedExecutionException - if the task cannot be scheduled for execution
      NullPointerException - if command or unit is null

    • schedule

      <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
      Submits a value-returning one-shot task that becomes enabled for execution after the given delay.
      Type Parameters:
      V - the type of the callable's result
      Parameters:
      callable - the function to execute
      delay - the time from now to delay execution
      unit - the time unit of the delay parameter
      Returns:
      a ScheduledFuture that can be used to extract result or cancel
      Throws:
      RejectedExecutionException - if the task cannot be scheduled for execution
      NullPointerException - if callable or unit is null

    • scheduleAtFixedRate

      ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
      Submits a periodic action that becomes enabled for execution first after the given initial delay, and subsequently with the given period; that is, executions will commence after initialDelay, then initialDelay + period, then initialDelay + 2 * period, and so on.

      The sequence of task executions continues indefinitely until one of the following exceptional completions occur:

      • The task is explicitly cancelled via the returned future.
      • The executor terminates, also resulting in task cancellation.
      • An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.
      Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

      If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.

      Parameters:
      command - the task to execute
      initialDelay - the time to delay first execution
      period - the period between successive executions
      unit - the time unit of the initialDelay and period parameters
      Returns:
      a ScheduledFuture representing pending completion of the series of repeated tasks. The future's 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
      NullPointerException - if command or unit is null
      IllegalArgumentException - if period less than or equal to zero

    • scheduleWithFixedDelay

      ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
      Submits a periodic action that becomes enabled for execution first after the given initial delay, and subsequently with the given delay between the termination of one execution and the commencement of the next.

      The sequence of task executions continues indefinitely until one of the following exceptional completions occur:

      • The task is explicitly cancelled via the returned future.
      • The executor terminates, also resulting in task cancellation.
      • An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.
      Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.
      Parameters:
      command - the task to execute
      initialDelay - the time to delay first execution
      delay - the delay between the termination of one execution and the commencement of the next
      unit - the time unit of the initialDelay and delay parameters
      Returns:
      a ScheduledFuture representing pending completion of the series of repeated tasks. The future's 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
      NullPointerException - if command or unit is null
      IllegalArgumentException - if delay less than or equal to zero