ScheduledExecutorService
public
interface
ScheduledExecutorService
implements
ExecutorService
java.util.concurrent.ScheduledExecutorService
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Known indirect subclasses
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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);
}
}
Summary
Public methods |
abstract
<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.
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abstract
ScheduledFuture<?>
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schedule(Runnable command, long delay, TimeUnit unit)
Submits a one-shot task that becomes enabled after the given delay.
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abstract
ScheduledFuture<?>
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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.
|
abstract
ScheduledFuture<?>
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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.
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Inherited methods |
From interface
java.util.concurrent.ExecutorService
abstract
boolean
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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.
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default
void
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close()
Initiates an orderly shutdown in which previously submitted tasks are
executed, but no new tasks will be accepted.
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abstract
<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.
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abstract
<T>
List<Future<T>>
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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.
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abstract
<T>
T
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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.
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abstract
<T>
T
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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.
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abstract
boolean
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isShutdown()
Returns true if this executor has been shut down.
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abstract
boolean
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isTerminated()
Returns true if all tasks have completed following shut down.
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abstract
void
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shutdown()
Initiates an orderly shutdown in which previously submitted
tasks are executed, but no new tasks will be accepted.
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abstract
List<Runnable>
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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.
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abstract
Future<?>
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submit(Runnable task)
Submits a Runnable task for execution and returns a Future
representing that task.
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abstract
<T>
Future<T>
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submit(Callable<T> task)
Submits a value-returning task for execution and returns a
Future representing the pending results of the task.
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abstract
<T>
Future<T>
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submit(Runnable task, T result)
Submits a Runnable task for execution and returns a Future
representing that task.
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From interface
java.lang.AutoCloseable
abstract
void
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close()
Closes this resource, relinquishing any underlying resources.
|
|
From interface
java.util.concurrent.Executor
abstract
void
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execute(Runnable command)
Executes the given command at some time in the future.
|
|
Public methods
schedule
public abstract ScheduledFuture<V> schedule (Callable<V> callable,
long delay,
TimeUnit unit)
Submits a value-returning one-shot task that becomes enabled
after the given delay.
Parameters |
callable |
Callable : the function to execute |
delay |
long : the time from now to delay execution |
unit |
TimeUnit : the time unit of the delay parameter |
Returns |
ScheduledFuture<V> |
a ScheduledFuture that can be used to extract result or cancel |
schedule
public abstract ScheduledFuture<?> schedule (Runnable command,
long delay,
TimeUnit unit)
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 |
Returns |
ScheduledFuture<?> |
a ScheduledFuture representing pending completion of
the task and whose get() method will return
null upon completion |
scheduleAtFixedRate
public abstract 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.
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 |
Returns |
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. |
scheduleWithFixedDelay
public abstract 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
.
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 |
Returns |
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. |