ScheduledThreadPoolExecutor
open class ScheduledThreadPoolExecutor : ThreadPoolExecutor, ScheduledExecutorService
kotlin.Any | |||
↳ | java.util.concurrent.AbstractExecutorService | ||
↳ | java.util.concurrent.ThreadPoolExecutor | ||
↳ | java.util.concurrent.ScheduledThreadPoolExecutor |
A ThreadPoolExecutor
that can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable to java.util.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.
Successive executions of a periodic 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.
As with ThreadPoolExecutor
, if not otherwise specified, this class uses Executors#defaultThreadFactory
as the default thread factory, and ThreadPoolExecutor.AbortPolicy
as the default rejected execution handler.
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:
<code>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. }</code>
Summary
Public constructors | |
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ScheduledThreadPoolExecutor(corePoolSize: Int) Creates a new |
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ScheduledThreadPoolExecutor(corePoolSize: Int, threadFactory: ThreadFactory!) Creates a new |
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ScheduledThreadPoolExecutor(corePoolSize: Int, handler: RejectedExecutionHandler!) Creates a new |
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ScheduledThreadPoolExecutor(corePoolSize: Int, threadFactory: ThreadFactory!, handler: RejectedExecutionHandler!) Creates a new |
Public methods | |
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open Unit |
Executes |
open Boolean |
Gets the policy on whether to continue executing existing periodic tasks even when this executor has been |
open Boolean |
Gets the policy on whether to execute existing delayed tasks even when this executor has been |
open BlockingQueue<Runnable!>! |
getQueue() Returns the task queue used by this executor. |
open Boolean |
Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. |
open ScheduledFuture<*>! | |
open ScheduledFuture<V>! | |
open 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 |
open 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. |
open Unit |
Sets the policy on whether to continue executing existing periodic tasks even when this executor has been |
open Unit |
Sets the policy on whether to execute existing delayed tasks even when this executor has been |
open Unit |
setRemoveOnCancelPolicy(value: Boolean) Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. |
open Unit |
shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. |
open MutableList<Runnable!>! |
Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. |
open Future<*>! | |
open Future<T>! | |
open Future<T>! |
Protected methods | |
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open RunnableScheduledFuture<V>! |
decorateTask(runnable: Runnable!, task: RunnableScheduledFuture<V>!) Modifies or replaces the task used to execute a runnable. |
open RunnableScheduledFuture<V>! |
decorateTask(callable: Callable<V>!, task: RunnableScheduledFuture<V>!) Modifies or replaces the task used to execute a callable. |
Inherited functions | |
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Public constructors
ScheduledThreadPoolExecutor
ScheduledThreadPoolExecutor(corePoolSize: Int)
Creates a new ScheduledThreadPoolExecutor
with the given core pool size.
Parameters | |
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corePoolSize |
Int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set |
Exceptions | |
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java.lang.IllegalArgumentException |
if corePoolSize < 0 |
ScheduledThreadPoolExecutor
ScheduledThreadPoolExecutor(
corePoolSize: Int,
threadFactory: ThreadFactory!)
Creates a new ScheduledThreadPoolExecutor
with the given initial parameters.
Parameters | |
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corePoolSize |
Int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set |
threadFactory |
ThreadFactory!: the factory to use when the executor creates a new thread |
Exceptions | |
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java.lang.IllegalArgumentException |
if corePoolSize < 0 |
java.lang.NullPointerException |
if threadFactory is null |
ScheduledThreadPoolExecutor
ScheduledThreadPoolExecutor(
corePoolSize: Int,
handler: RejectedExecutionHandler!)
Creates a new ScheduledThreadPoolExecutor
with the given initial parameters.
Parameters | |
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corePoolSize |
Int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set |
handler |
RejectedExecutionHandler!: the handler to use when execution is blocked because the thread bounds and queue capacities are reached |
Exceptions | |
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java.lang.IllegalArgumentException |
if corePoolSize < 0 |
java.lang.NullPointerException |
if handler is null |
ScheduledThreadPoolExecutor
ScheduledThreadPoolExecutor(
corePoolSize: Int,
threadFactory: ThreadFactory!,
handler: RejectedExecutionHandler!)
Creates a new ScheduledThreadPoolExecutor
with the given initial parameters.
Parameters | |
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corePoolSize |
Int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set |
threadFactory |
ThreadFactory!: the factory to use when the executor creates a new thread |
handler |
RejectedExecutionHandler!: the handler to use when execution is blocked because the thread bounds and queue capacities are reached |
Exceptions | |
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java.lang.IllegalArgumentException |
if corePoolSize < 0 |
java.lang.NullPointerException |
if threadFactory or handler is null |
Public methods
execute
open fun execute(command: Runnable!): Unit
Executes 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 java.util.concurrent.Future#get.
Parameters | |
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command |
Runnable!: the runnable task |
Exceptions | |
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java.util.concurrent.RejectedExecutionException |
at discretion of RejectedExecutionHandler , if the task cannot be accepted for execution because the executor has been shut down |
java.lang.NullPointerException |
if command is null |
getContinueExistingPeriodicTasksAfterShutdownPolicy
open fun getContinueExistingPeriodicTasksAfterShutdownPolicy(): Boolean
Gets the policy on whether to continue executing existing periodic tasks even when this executor has been shutdown
. In this case, executions will continue until shutdownNow
or the policy is set to false
when already shutdown. This value is by default false
.
Return | |
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Boolean |
true if will continue after shutdown |
getExecuteExistingDelayedTasksAfterShutdownPolicy
open fun getExecuteExistingDelayedTasksAfterShutdownPolicy(): Boolean
Gets the policy on whether to execute existing delayed tasks even when this executor has been 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
.
Return | |
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Boolean |
true if will execute after shutdown |
getQueue
open fun getQueue(): BlockingQueue<Runnable!>!
Returns the task queue used by this executor. Access to the task queue is intended primarily for debugging and monitoring. This queue may be in active use. Retrieving the task queue does not prevent queued tasks from executing.
Each element of this queue is a ScheduledFuture
. For tasks submitted via one of the schedule
methods, the element will be identical to the returned ScheduledFuture
. For tasks submitted using execute
, the element will be a zero-delay ScheduledFuture
.
Iteration over this queue is not guaranteed to traverse tasks in the order in which they will execute.
Return | |
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BlockingQueue<Runnable!>! |
the task queue |
getRemoveOnCancelPolicy
open fun getRemoveOnCancelPolicy(): Boolean
Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by default false
.
Return | |
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Boolean |
true if cancelled tasks are immediately removed from the queue |
See Also
schedule
open fun schedule(
command: Runnable!,
delay: Long,
unit: TimeUnit!
): ScheduledFuture<*>!
Parameters | |
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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 | |
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ScheduledFuture<*>! |
a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion |
Exceptions | |
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java.util.concurrent.RejectedExecutionException |
if the task cannot be scheduled for execution |
java.lang.NullPointerException |
if command or unit is null |
schedule
open fun <V : Any!> schedule(
callable: Callable<V>!,
delay: Long,
unit: TimeUnit!
): ScheduledFuture<V>!
Parameters | |
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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 | |
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ScheduledFuture<V>! |
a ScheduledFuture that can be used to extract result or cancel |
Exceptions | |
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java.util.concurrent.RejectedExecutionException |
if the task cannot be scheduled for execution |
java.lang.NullPointerException |
if callable or unit is null |
scheduleAtFixedRate
open 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.
- Method
shutdown
is called and the policy on is not set true, or methodshutdownNow
is called; also resulting in task cancellation. - An execution of the task throws an exception. In this case calling
get
on the returned future will throwExecutionException
, holding the exception as its cause.
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 | |
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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 | |
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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 | |
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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
open 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.
- Method
shutdown
is called and the policy on is not set true, or methodshutdownNow
is called; also resulting in task cancellation. - An execution of the task throws an exception. In this case calling
get
on the returned future will throwExecutionException
, holding the exception as its cause.
isDone()
on the returned future will return true
.
Parameters | |
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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 | |
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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 | |
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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 |
setContinueExistingPeriodicTasksAfterShutdownPolicy
open fun setContinueExistingPeriodicTasksAfterShutdownPolicy(value: Boolean): Unit
Sets the policy on whether to continue executing existing periodic tasks even when this executor has been shutdown
. In this case, executions will continue until shutdownNow
or the policy is set to false
when already shutdown. This value is by default false
.
Parameters | |
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value |
Boolean: if true , continue after shutdown, else don't |
setExecuteExistingDelayedTasksAfterShutdownPolicy
open fun setExecuteExistingDelayedTasksAfterShutdownPolicy(value: Boolean): Unit
Sets the policy on whether to execute existing delayed tasks even when this executor has been 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
.
Parameters | |
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value |
Boolean: if true , execute after shutdown, else don't |
setRemoveOnCancelPolicy
open fun setRemoveOnCancelPolicy(value: Boolean): Unit
Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by default false
.
Parameters | |
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value |
Boolean: if true , remove on cancellation, else don't |
See Also
shutdown
open fun shutdown(): Unit
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.
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.
shutdownNow
open fun shutdownNow(): MutableList<Runnable!>!
Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. These tasks are drained (removed) from the task queue upon return from this method.
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 interrupts tasks via Thread#interrupt
; any task that fails to respond to interrupts may never terminate.
Return | |
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MutableList<Runnable!>! |
list of tasks that never commenced execution. Each element of this list is a ScheduledFuture . For tasks submitted via one of the schedule methods, the element will be identical to the returned ScheduledFuture . For tasks submitted using execute , the element will be a zero-delay ScheduledFuture . |
submit
open fun submit(task: Runnable!): Future<*>!
Parameters | |
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task |
Runnable!: the task to submit |
Return | |
---|---|
Future<*>! |
a Future representing pending completion of the task |
Exceptions | |
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java.util.concurrent.RejectedExecutionException |
if the task cannot be scheduled for execution |
java.lang.NullPointerException |
if the task is null |
submit
open fun <T : Any!> submit(
task: Runnable!,
result: T
): Future<T>!
Parameters | |
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task |
Runnable!: the task to submit |
result |
T: the result to return |
<T> |
the type of the result |
Return | |
---|---|
Future<T>! |
a Future representing pending completion of the task |
Exceptions | |
---|---|
java.util.concurrent.RejectedExecutionException |
if the task cannot be scheduled for execution |
java.lang.NullPointerException |
if the task is null |
submit
open fun <T : Any!> submit(task: Callable<T>!): Future<T>!
Parameters | |
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task |
Callable<T>!: the task to submit |
<T> |
the type of the task's result |
Return | |
---|---|
Future<T>! |
a Future representing pending completion of the task |
Exceptions | |
---|---|
java.util.concurrent.RejectedExecutionException |
if the task cannot be scheduled for execution |
java.lang.NullPointerException |
if the task is null |
Protected methods
decorateTask
protected open fun <V : Any!> decorateTask(
runnable: Runnable!,
task: RunnableScheduledFuture<V>!
): RunnableScheduledFuture<V>!
Modifies or replaces the task used to execute a runnable. This method can be used to override the concrete class used for managing internal tasks. The default implementation simply returns the given task.
Parameters | |
---|---|
runnable |
Runnable!: the submitted Runnable |
task |
RunnableScheduledFuture<V>!: the task created to execute the runnable |
<V> |
the type of the task's result |
Return | |
---|---|
RunnableScheduledFuture<V>! |
a task that can execute the runnable |
decorateTask
protected open fun <V : Any!> decorateTask(
callable: Callable<V>!,
task: RunnableScheduledFuture<V>!
): RunnableScheduledFuture<V>!
Modifies or replaces the task used to execute a callable. This method can be used to override the concrete class used for managing internal tasks. The default implementation simply returns the given task.
Parameters | |
---|---|
callable |
Callable<V>!: the submitted Callable |
task |
RunnableScheduledFuture<V>!: the task created to execute the callable |
<V> |
the type of the task's result |
Return | |
---|---|
RunnableScheduledFuture<V>! |
a task that can execute the callable |