Module java.base
Package java.util.concurrent

Interface ScheduledExecutorService

All Superinterfaces:
Executor, ExecutorService
All Known Implementing Classes:
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 a task object that can be used to cancel or check execution. The 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 Details

    • schedule

      ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
      Submits a one-shot task that becomes enabled 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 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 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.

      CRaC:
      Since the execution is suspended after a checkpoint the timer could execute many times after a restore, catching up for all the delayed executions. If this is not desirable the application can cancel the task before checkpoint and schedule it again after restore.
      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 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.
      CRaC:
      Since the execution is suspended after a checkpoint the timer could execute many times after a restore, catching up for all the delayed executions. If this is not desirable the application can cancel the task before checkpoint and schedule it again after restore.
      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