Added in API level 1

ScheduledExecutorService

interface ScheduledExecutorService : ExecutorService

java.util.concurrent.ScheduledExecutorService

Known Direct Subclasses ScheduledThreadPoolExecutor ScheduledThreadPoolExecutor A ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically.

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 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:

<code>import static java.util.concurrent.TimeUnit.*;
  class BeeperControl {
    private final ScheduledExecutorService scheduler =
      Executors.newScheduledThreadPool(1);
 
    public void beepForAnHour() {
      Runnable beeper = () -&gt; System.out.println("beep");
      ScheduledFuture&lt;?&gt; beeperHandle =
        scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
      Runnable canceller = () -&gt; beeperHandle.cancel(false);
      scheduler.schedule(canceller, 1, HOURS);
    }
  }</code>

Summary

Public methods
abstract ScheduledFuture<*>!	schedule(command: Runnable!, delay: Long, unit: TimeUnit!) Submits a one-shot task that becomes enabled after the given delay.
abstract ScheduledFuture<V>!	schedule(callable: Callable<V>!, delay: Long, unit: TimeUnit!) Submits a value-returning one-shot task that becomes enabled after the given delay.
abstract ScheduledFuture<*>!	scheduleAtFixedRate(command: Runnable!, initialDelay: Long, period: Long, unit: TimeUnit!) 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.
abstract ScheduledFuture<*>!	scheduleWithFixedDelay(command: Runnable!, initialDelay: Long, delay: Long, unit: TimeUnit!) 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.

Inherited functions
From class ExecutorService Boolean awaitTermination(timeout: Long, unit: TimeUnit!) Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first. Unit close() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. This method waits until all tasks have completed execution and the executor has terminated. If interrupted while waiting, this method stops all executing tasks as if by invoking shutdownNow(). It then continues to wait until all actively executing tasks have completed. Tasks that were awaiting execution are not executed. The interrupt status will be re-asserted before this method returns. If already terminated, invoking this method has no effect. MutableList<Future<T>!>! invokeAll(tasks: MutableCollection<out Callable<T>!>!) Executes the given tasks, returning a list of Futures holding their status and results when all complete. Future.isDone is true for each element of the returned list. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress. MutableList<Future<T>!>! invokeAll(tasks: MutableCollection<out Callable<T>!>!, timeout: Long, unit: TimeUnit!) Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. Future.isDone is true for each element of the returned list. Upon return, tasks that have not completed are cancelled. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress. T invokeAny(tasks: MutableCollection<out Callable<T>!>!) Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress. T invokeAny(tasks: MutableCollection<out Callable<T>!>!, timeout: Long, unit: TimeUnit!) 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. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress. Boolean isShutdown() Returns true if this executor has been shut down. Boolean isTerminated() Returns true if all tasks have completed following shut down. Note that isTerminated is never true unless either shutdown or shutdownNow was called first. Unit shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down. This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that. MutableList<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. This method does not wait for actively executing tasks to terminate. Use awaitTermination to do that. There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via Thread.interrupt, so any task that fails to respond to interrupts may never terminate. Future<*>! submit(task: Runnable!) Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return null upon successful completion. Future<T>! submit(task: Runnable!, result: T) Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return the given result upon successful completion. Future<T>! submit(task: Callable<T>!) Submits a value-returning task for execution and returns a Future representing the pending results of the task. The Future's get method will return the task's result upon successful completion. If you would like to immediately block waiting for a task, you can use constructions of the form result = exec.submit(aCallable).get(); Note: The Executors class includes a set of methods that can convert some other common closure-like objects, for example, java.security.PrivilegedAction to Callable form so they can be submitted.
From class Executor Unit execute(command: Runnable!) Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the Executor implementation.

Public methods

schedule

Added in API level 1

abstract fun schedule(
    command: Runnable!, 
    delay: Long, 
    unit: TimeUnit!
): ScheduledFuture<*>!

Submits a one-shot task that becomes enabled after the given delay.

Parameters
command	Runnable!: the task to execute
delay	Long: the time from now to delay execution
unit	TimeUnit!: the time unit of the delay parameter

Return
ScheduledFuture<*>!	a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion

Exceptions
java.util.concurrent.RejectedExecutionException	if the task cannot be scheduled for execution
java.lang.NullPointerException	if command or unit is null

schedule

Added in API level 1

abstract fun <V : Any!> schedule(
    callable: Callable<V>!, 
    delay: Long, 
    unit: TimeUnit!
): ScheduledFuture<V>!

Submits a value-returning one-shot task that becomes enabled after the given delay.

Parameters
callable	Callable<V>!: the function to execute
delay	Long: the time from now to delay execution
unit	TimeUnit!: the time unit of the delay parameter
<V>	the type of the callable's result

Return
ScheduledFuture<V>!	a ScheduledFuture that can be used to extract result or cancel

Exceptions
java.util.concurrent.RejectedExecutionException	if the task cannot be scheduled for execution
java.lang.NullPointerException	if callable or unit is null

scheduleAtFixedRate

Added in API level 1

abstract fun scheduleAtFixedRate(
    command: Runnable!, 
    initialDelay: Long, 
    period: Long, 
    unit: TimeUnit!
): ScheduledFuture<*>!

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.

Parameters
command	Runnable!: the task to execute
initialDelay	Long: the time to delay first execution
period	Long: the period between successive executions
unit	TimeUnit!: the time unit of the initialDelay and period parameters

Return
ScheduledFuture<*>!	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.

Exceptions
java.util.concurrent.RejectedExecutionException	if the task cannot be scheduled for execution
java.lang.NullPointerException	if command or unit is null
java.lang.IllegalArgumentException	if period less than or equal to zero

scheduleWithFixedDelay

Added in API level 1

abstract fun scheduleWithFixedDelay(
    command: Runnable!, 
    initialDelay: Long, 
    delay: Long, 
    unit: TimeUnit!
): ScheduledFuture<*>!

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.

Parameters
command	Runnable!: the task to execute
initialDelay	Long: the time to delay first execution
delay	Long: the delay between the termination of one execution and the commencement of the next
unit	TimeUnit!: the time unit of the initialDelay and delay parameters

Return
ScheduledFuture<*>!	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.

Exceptions
java.util.concurrent.RejectedExecutionException	if the task cannot be scheduled for execution
java.lang.NullPointerException	if command or unit is null
java.lang.IllegalArgumentException	if delay less than or equal to zero