public class ScheduledThreadPoolExecutor extends ThreadPoolExecutor implements ScheduledExecutorService
ThreadPoolExecutor that can additionally schedule
commands to run after a given delay, or to execute
periodically. This class is preferable to Timer
when multiple worker threads are needed, or when the additional
flexibility or capabilities of ThreadPoolExecutor (which
this class extends) are required.
Delayed tasks execute no sooner than they are enabled, but without any real-time guarantees about when, after they are enabled, they will commence. Tasks scheduled for exactly the same execution time are enabled in first-in-first-out (FIFO) order of submission.
When a submitted task is cancelled before it is run, execution
is suppressed. By default, such a cancelled task is not
automatically removed from the work queue until its delay
elapses. While this enables further inspection and monitoring, it
may also cause unbounded retention of cancelled tasks. To avoid
this, set setRemoveOnCancelPolicy(boolean) to true, which
causes tasks to be immediately removed from the work queue at
time of cancellation.
Successive executions of a task scheduled via
scheduleAtFixedRate or
scheduleWithFixedDelay do not overlap. While different
executions may be performed by different threads, the effects of
prior executions happen-before
those of subsequent ones.
While this class inherits from ThreadPoolExecutor, a few
of the inherited tuning methods are not useful for it. In
particular, because it acts as a fixed-sized pool using
corePoolSize threads and an unbounded queue, adjustments
to maximumPoolSize have no useful effect. Additionally, it
is almost never a good idea to set corePoolSize to zero or
use allowCoreThreadTimeOut because this may leave the pool
without threads to handle tasks once they become eligible to run.
Extension notes: This class overrides the
execute and
submit
methods to generate internal ScheduledFuture objects to
control per-task delays and scheduling. To preserve
functionality, any further overrides of these methods in
subclasses must invoke superclass versions, which effectively
disables additional task customization. However, this class
provides alternative protected extension method
decorateTask (one version each for Runnable and
Callable) that can be used to customize the concrete task
types used to execute commands entered via execute,
submit, schedule, scheduleAtFixedRate,
and scheduleWithFixedDelay. By default, a
ScheduledThreadPoolExecutor uses a task type extending
FutureTask. However, this may be modified or replaced using
subclasses of the form:
public class CustomScheduledExecutor extends ScheduledThreadPoolExecutor {
static class CustomTask<V> implements RunnableScheduledFuture<V> { ... }
protected <V> RunnableScheduledFuture<V> decorateTask(
Runnable r, RunnableScheduledFuture<V> task) {
return new CustomTask<V>(r, task);
}
protected <V> RunnableScheduledFuture<V> decorateTask(
Callable<V> c, RunnableScheduledFuture<V> task) {
return new CustomTask<V>(c, task);
}
// ... add constructors, etc.
}ThreadPoolExecutor.AbortPolicy, ThreadPoolExecutor.CallerRunsPolicy, ThreadPoolExecutor.DiscardOldestPolicy, ThreadPoolExecutor.DiscardPolicy| Constructor | Description |
|---|---|
ScheduledThreadPoolExecutor(int corePoolSize) |
Creates a new
ScheduledThreadPoolExecutor with the
given core pool size. |
ScheduledThreadPoolExecutor(int corePoolSize,
RejectedExecutionHandler handler) |
Creates a new ScheduledThreadPoolExecutor with the given
initial parameters.
|
ScheduledThreadPoolExecutor(int corePoolSize,
ThreadFactory threadFactory) |
Creates a new
ScheduledThreadPoolExecutor with the
given initial parameters. |
ScheduledThreadPoolExecutor(int corePoolSize,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) |
Creates a new ScheduledThreadPoolExecutor with the given
initial parameters.
|
| Modifier and Type | Method | Description |
|---|---|---|
protected <V> RunnableScheduledFuture<V> |
decorateTask(Callable<V> callable,
RunnableScheduledFuture<V> task) |
Modifies or replaces the task used to execute a callable.
|
protected <V> RunnableScheduledFuture<V> |
decorateTask(Runnable runnable,
RunnableScheduledFuture<V> task) |
Modifies or replaces the task used to execute a runnable.
|
void |
execute(Runnable command) |
Executes
command with zero required delay. |
boolean |
getContinueExistingPeriodicTasksAfterShutdownPolicy() |
Gets the policy on whether to continue executing existing
periodic tasks even when this executor has been
shutdown. |
boolean |
getExecuteExistingDelayedTasksAfterShutdownPolicy() |
Gets the policy on whether to execute existing delayed
tasks even when this executor has been
shutdown. |
BlockingQueue<Runnable> |
getQueue() |
Returns the task queue used by this executor.
|
boolean |
getRemoveOnCancelPolicy() |
Gets the policy on whether cancelled tasks should be immediately
removed from the work queue at time of cancellation.
|
<V> ScheduledFuture<V> |
schedule(Callable<V> callable,
long delay,
TimeUnit unit) |
Creates and executes a ScheduledFuture that becomes enabled after the
given delay.
|
ScheduledFuture<?> |
schedule(Runnable command,
long delay,
TimeUnit unit) |
Creates and executes a one-shot action that becomes enabled
after the given delay.
|
ScheduledFuture<?> |
scheduleAtFixedRate(Runnable command,
long initialDelay,
long period,
TimeUnit unit) |
Creates and executes 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. |
ScheduledFuture<?> |
scheduleWithFixedDelay(Runnable command,
long initialDelay,
long delay,
TimeUnit unit) |
Creates and executes 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.
|
void |
setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) |
Sets the policy on whether to continue executing existing
periodic tasks even when this executor has been
shutdown. |
void |
setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value) |
Sets the policy on whether to execute existing delayed
tasks even when this executor has been
shutdown. |
void |
setRemoveOnCancelPolicy(boolean value) |
Sets the policy on whether cancelled tasks should be immediately
removed from the work queue at time of cancellation.
|
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.
|
<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.
|
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.
|
afterExecute, allowCoreThreadTimeOut, allowsCoreThreadTimeOut, awaitTermination, beforeExecute, finalize, getActiveCount, getCompletedTaskCount, getCorePoolSize, getKeepAliveTime, getLargestPoolSize, getMaximumPoolSize, getPoolSize, getRejectedExecutionHandler, getTaskCount, getThreadFactory, isShutdown, isTerminated, isTerminating, prestartAllCoreThreads, prestartCoreThread, purge, remove, setCorePoolSize, setKeepAliveTime, setMaximumPoolSize, setRejectedExecutionHandler, setThreadFactory, terminated, toStringinvokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskForclone, equals, getClass, hashCode, notify, notifyAll, wait, wait, waitawaitTermination, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminatedpublic ScheduledThreadPoolExecutor(int corePoolSize)
ScheduledThreadPoolExecutor with the
given core pool size.corePoolSize - the number of threads to keep in the pool, even
if they are idle, unless allowCoreThreadTimeOut is setIllegalArgumentException - if corePoolSize < 0public ScheduledThreadPoolExecutor(int corePoolSize,
ThreadFactory threadFactory)
ScheduledThreadPoolExecutor with the
given initial parameters.corePoolSize - the number of threads to keep in the pool, even
if they are idle, unless allowCoreThreadTimeOut is setthreadFactory - the factory to use when the executor
creates a new threadIllegalArgumentException - if corePoolSize < 0NullPointerException - if threadFactory is nullpublic ScheduledThreadPoolExecutor(int corePoolSize,
RejectedExecutionHandler handler)
corePoolSize - the number of threads to keep in the pool, even
if they are idle, unless allowCoreThreadTimeOut is sethandler - the handler to use when execution is blocked
because the thread bounds and queue capacities are reachedIllegalArgumentException - if corePoolSize < 0NullPointerException - if handler is nullpublic ScheduledThreadPoolExecutor(int corePoolSize,
ThreadFactory threadFactory,
RejectedExecutionHandler handler)
corePoolSize - the number of threads to keep in the pool, even
if they are idle, unless allowCoreThreadTimeOut is setthreadFactory - the factory to use when the executor
creates a new threadhandler - the handler to use when execution is blocked
because the thread bounds and queue capacities are reachedIllegalArgumentException - if corePoolSize < 0NullPointerException - if threadFactory or
handler is nullprotected <V> RunnableScheduledFuture<V> decorateTask(Runnable runnable, RunnableScheduledFuture<V> task)
V - the type of the task's resultrunnable - the submitted Runnabletask - the task created to execute the runnableprotected <V> RunnableScheduledFuture<V> decorateTask(Callable<V> callable, RunnableScheduledFuture<V> task)
V - the type of the task's resultcallable - the submitted Callabletask - the task created to execute the callablepublic ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
ScheduledExecutorServiceschedule in interface ScheduledExecutorServicecommand - the task to executedelay - the time from now to delay executionunit - the time unit of the delay parameterget() method will return
null upon completionRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if command is nullpublic <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
ScheduledExecutorServiceschedule in interface ScheduledExecutorServiceV - the type of the callable's resultcallable - the function to executedelay - the time from now to delay executionunit - the time unit of the delay parameterRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if callable is nullpublic ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
ScheduledExecutorServiceinitialDelay then initialDelay+period, then
initialDelay + 2 * period, and so on.
If any execution of the task
encounters an exception, subsequent executions are suppressed.
Otherwise, the task will only terminate via cancellation or
termination of the executor. If any execution of this task
takes longer than its period, then subsequent executions
may start late, but will not concurrently execute.scheduleAtFixedRate in interface ScheduledExecutorServicecommand - the task to executeinitialDelay - the time to delay first executionperiod - the period between successive executionsunit - the time unit of the initialDelay and period parametersget() method will throw an
exception upon cancellationRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if command is nullIllegalArgumentException - if period less than or equal to zeropublic ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
ScheduledExecutorServicescheduleWithFixedDelay in interface ScheduledExecutorServicecommand - the task to executeinitialDelay - the time to delay first executiondelay - the delay between the termination of one
execution and the commencement of the nextunit - the time unit of the initialDelay and delay parametersget() method will throw an
exception upon cancellationRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if command is nullIllegalArgumentException - if delay less than or equal to zeropublic void execute(Runnable command)
command with zero required delay.
This has effect equivalent to
schedule(command, 0, anyUnit).
Note that inspections of the queue and of the list returned by
shutdownNow will access the zero-delayed
ScheduledFuture, not the command itself.
A consequence of the use of ScheduledFuture objects is
that afterExecute is always
called with a null second Throwable argument, even if the
command terminated abruptly. Instead, the Throwable
thrown by such a task can be obtained via Future.get().
execute in interface Executorexecute in class ThreadPoolExecutorcommand - the task to executeRejectedExecutionException - at discretion of
RejectedExecutionHandler, if the task
cannot be accepted for execution because the
executor has been shut downNullPointerException - if command is nullpublic Future<?> submit(Runnable task)
ExecutorServiceget method will
return null upon successful completion.submit in interface ExecutorServicesubmit in class AbstractExecutorServicetask - the task to submitRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if the task is nullpublic <T> Future<T> submit(Runnable task, T result)
ExecutorServiceget method will
return the given result upon successful completion.submit in interface ExecutorServicesubmit in class AbstractExecutorServiceT - the type of the resulttask - the task to submitresult - the result to returnRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if the task is nullpublic <T> Future<T> submit(Callable<T> task)
ExecutorServiceget 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, PrivilegedAction to
Callable form so they can be submitted.
submit in interface ExecutorServicesubmit in class AbstractExecutorServiceT - the type of the task's resulttask - the task to submitRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if the task is nullpublic void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value)
shutdown.
In this case, these tasks will only terminate upon
shutdownNow or after setting the policy to
false when already shutdown.
This value is by default false.value - if true, continue after shutdown, else don'tgetContinueExistingPeriodicTasksAfterShutdownPolicy()public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy()
shutdown.
In this case, these tasks will only terminate upon
shutdownNow or after setting the policy to
false when already shutdown.
This value is by default false.true if will continue after shutdownsetContinueExistingPeriodicTasksAfterShutdownPolicy(boolean)public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)
shutdown.
In this case, these tasks will only terminate upon
shutdownNow, or after setting the policy to
false when already shutdown.
This value is by default true.value - if true, execute after shutdown, else don'tgetExecuteExistingDelayedTasksAfterShutdownPolicy()public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy()
shutdown.
In this case, these tasks will only terminate upon
shutdownNow, or after setting the policy to
false when already shutdown.
This value is by default true.true if will execute after shutdownsetExecuteExistingDelayedTasksAfterShutdownPolicy(boolean)public void setRemoveOnCancelPolicy(boolean value)
false.value - if true, remove on cancellation, else don'tgetRemoveOnCancelPolicy()public boolean getRemoveOnCancelPolicy()
false.true if cancelled tasks are immediately removed
from the queuesetRemoveOnCancelPolicy(boolean)public void shutdown()
This method does not wait for previously submitted tasks to
complete execution. Use awaitTermination
to do that.
If the ExecuteExistingDelayedTasksAfterShutdownPolicy
has been set false, existing delayed tasks whose delays
have not yet elapsed are cancelled. And unless the ContinueExistingPeriodicTasksAfterShutdownPolicy has been set
true, future executions of existing periodic tasks will
be cancelled.
shutdown in interface ExecutorServiceshutdown in class ThreadPoolExecutorSecurityException - if a security manager exists and
shutting down this ExecutorService may manipulate
threads that the caller is not permitted to modify
because it does not hold RuntimePermission("modifyThread"),
or the security manager's checkAccess method
denies access.public List<Runnable> shutdownNow()
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. This implementation
cancels tasks via Thread.interrupt(), so any task that
fails to respond to interrupts may never terminate.
shutdownNow in interface ExecutorServiceshutdownNow in class ThreadPoolExecutorScheduledFuture,
including those tasks submitted using execute,
which are for scheduling purposes used as the basis of a
zero-delay ScheduledFuture.SecurityException - if a security manager exists and
shutting down this ExecutorService may manipulate
threads that the caller is not permitted to modify
because it does not hold RuntimePermission("modifyThread"),
or the security manager's checkAccess method
denies access.public BlockingQueue<Runnable> getQueue()
ScheduledFuture, including those
tasks submitted using execute which are for scheduling
purposes used as the basis of a zero-delay
ScheduledFuture. Iteration over this queue is
not guaranteed to traverse tasks in the order in
which they will execute.getQueue in class ThreadPoolExecutor Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2025, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.