- java.lang.Object
-
- java.util.concurrent.AbstractExecutorService
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- java.util.concurrent.ThreadPoolExecutor
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- java.util.concurrent.ScheduledThreadPoolExecutor
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- All Implemented Interfaces:
- Executor, ExecutorService, ScheduledExecutorService
public class ScheduledThreadPoolExecutor extends ThreadPoolExecutor implements ScheduledExecutorService
AThreadPoolExecutor
that can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable toTimer
when multiple worker threads are needed, or when the additional flexibility or capabilities ofThreadPoolExecutor
(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)
totrue
, which causes tasks to be immediately removed from the work queue at time of cancellation.Successive executions of a task scheduled via
scheduleAtFixedRate
orscheduleWithFixedDelay
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 usingcorePoolSize
threads and an unbounded queue, adjustments tomaximumPoolSize
have no useful effect. Additionally, it is almost never a good idea to setcorePoolSize
to zero or useallowCoreThreadTimeOut
because this may leave the pool without threads to handle tasks once they become eligible to run.Extension notes: This class overrides the
execute
andsubmit
methods to generate internalScheduledFuture
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 methoddecorateTask
(one version each forRunnable
andCallable
) that can be used to customize the concrete task types used to execute commands entered viaexecute
,submit
,schedule
,scheduleAtFixedRate
, andscheduleWithFixedDelay
. By default, aScheduledThreadPoolExecutor
uses a task type extendingFutureTask
. 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. }
- Since:
- 1.5
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-
Nested Class Summary
-
Nested classes/interfaces inherited from class java.util.concurrent.ThreadPoolExecutor
ThreadPoolExecutor.AbortPolicy, ThreadPoolExecutor.CallerRunsPolicy, ThreadPoolExecutor.DiscardOldestPolicy, ThreadPoolExecutor.DiscardPolicy
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Constructor Summary
Constructors Constructor and Description ScheduledThreadPoolExecutor(int corePoolSize)
Creates a newScheduledThreadPoolExecutor
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 newScheduledThreadPoolExecutor
with the given initial parameters.ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler)
Creates a new ScheduledThreadPoolExecutor with the given initial parameters.
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Method Summary
Methods Modifier and Type Method and 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)
Executescommand
with zero required delay.boolean
getContinueExistingPeriodicTasksAfterShutdownPolicy()
Gets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown
.boolean
getExecuteExistingDelayedTasksAfterShutdownPolicy()
Gets the policy on whether to execute existing delayed tasks even when this executor has beenshutdown
.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 beenshutdown
.void
setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)
Sets the policy on whether to execute existing delayed tasks even when this executor has beenshutdown
.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.-
Methods inherited from class java.util.concurrent.ThreadPoolExecutor
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, toString
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Methods inherited from class java.util.concurrent.AbstractExecutorService
invokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskFor
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Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods inherited from interface java.util.concurrent.ExecutorService
awaitTermination, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminated
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Constructor Detail
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ScheduledThreadPoolExecutor
public ScheduledThreadPoolExecutor(int corePoolSize)
Creates a newScheduledThreadPoolExecutor
with the given core pool size.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is set- Throws:
IllegalArgumentException
- ifcorePoolSize < 0
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ScheduledThreadPoolExecutor
public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)
Creates a newScheduledThreadPoolExecutor
with the given initial parameters.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is setthreadFactory
- the factory to use when the executor creates a new thread- Throws:
IllegalArgumentException
- ifcorePoolSize < 0
NullPointerException
- ifthreadFactory
is null
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ScheduledThreadPoolExecutor
public ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler)
Creates a new ScheduledThreadPoolExecutor with the given initial parameters.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is sethandler
- the handler to use when execution is blocked because the thread bounds and queue capacities are reached- Throws:
IllegalArgumentException
- ifcorePoolSize < 0
NullPointerException
- ifhandler
is null
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ScheduledThreadPoolExecutor
public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler)
Creates a new ScheduledThreadPoolExecutor with the given initial parameters.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
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 reached- Throws:
IllegalArgumentException
- ifcorePoolSize < 0
NullPointerException
- ifthreadFactory
orhandler
is null
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Method Detail
-
decorateTask
protected <V> RunnableScheduledFuture<V> decorateTask(Runnable runnable, RunnableScheduledFuture<V> task)
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
- the submitted Runnabletask
- the task created to execute the runnable- Returns:
- a task that can execute the runnable
- Since:
- 1.6
-
decorateTask
protected <V> RunnableScheduledFuture<V> decorateTask(Callable<V> callable, RunnableScheduledFuture<V> task)
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
- the submitted Callabletask
- the task created to execute the callable- Returns:
- a task that can execute the callable
- Since:
- 1.6
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schedule
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
Description copied from interface:ScheduledExecutorService
Creates and executes a one-shot action that becomes enabled after the given delay.- Specified by:
schedule
in interfaceScheduledExecutorService
- Parameters:
command
- the task to executedelay
- the time from now to delay executionunit
- 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 executionNullPointerException
- if command is null
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schedule
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
Description copied from interface:ScheduledExecutorService
Creates and executes a ScheduledFuture that becomes enabled after the given delay.- Specified by:
schedule
in interfaceScheduledExecutorService
- Parameters:
callable
- the function to executedelay
- the time from now to delay executionunit
- 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 executionNullPointerException
- if callable is null
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scheduleAtFixedRate
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
Description copied from interface:ScheduledExecutorService
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. 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.- Specified by:
scheduleAtFixedRate
in interfaceScheduledExecutorService
- Parameters:
command
- the task to executeinitialDelay
- the time to delay first executionperiod
- the period between successive executionsunit
- the time unit of the initialDelay and period parameters- Returns:
- a ScheduledFuture representing pending completion of the task, and whose get() method will throw an exception upon cancellation
- Throws:
RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if command is nullIllegalArgumentException
- if period less than or equal to zero
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scheduleWithFixedDelay
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
Description copied from interface:ScheduledExecutorService
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. 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.- Specified by:
scheduleWithFixedDelay
in interfaceScheduledExecutorService
- Parameters:
command
- 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 parameters- Returns:
- a ScheduledFuture representing pending completion of the task, and whose get() method will throw an exception upon cancellation
- Throws:
RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if command is nullIllegalArgumentException
- if delay less than or equal to zero
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execute
public void execute(Runnable command)
Executescommand
with zero required delay. This has effect equivalent toschedule(command, 0, anyUnit)
. Note that inspections of the queue and of the list returned byshutdownNow
will access the zero-delayedScheduledFuture
, not thecommand
itself.A consequence of the use of
ScheduledFuture
objects is thatafterExecute
is always called with a null secondThrowable
argument, even if thecommand
terminated abruptly. Instead, theThrowable
thrown by such a task can be obtained viaFuture.get()
.- Specified by:
execute
in interfaceExecutor
- Overrides:
execute
in classThreadPoolExecutor
- Parameters:
command
- the task to execute- Throws:
RejectedExecutionException
- at discretion ofRejectedExecutionHandler
, if the task cannot be accepted for execution because the executor has been shut downNullPointerException
- ifcommand
is null
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submit
public Future<?> submit(Runnable task)
Description copied from interface:ExecutorService
Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return null upon successful completion.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- Parameters:
task
- the task to submit- Returns:
- a Future representing pending completion of the task
- Throws:
RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if the task is null
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submit
public <T> Future<T> submit(Runnable task, T result)
Description copied from interface:ExecutorService
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.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- Parameters:
task
- the task to submitresult
- the result to return- Returns:
- a Future representing pending completion of the task
- Throws:
RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if the task is null
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submit
public <T> Future<T> submit(Callable<T> task)
Description copied from interface:ExecutorService
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,PrivilegedAction
toCallable
form so they can be submitted.- Specified by:
submit
in interfaceExecutorService
- Overrides:
submit
in classAbstractExecutorService
- Parameters:
task
- the task to submit- Returns:
- a Future representing pending completion of the task
- Throws:
RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if the task is null
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setContinueExistingPeriodicTasksAfterShutdownPolicy
public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value)
Sets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown
. In this case, these tasks will only terminate uponshutdownNow
or after setting the policy tofalse
when already shutdown. This value is by defaultfalse
.- Parameters:
value
- iftrue
, continue after shutdown, else don't.- See Also:
getContinueExistingPeriodicTasksAfterShutdownPolicy()
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getContinueExistingPeriodicTasksAfterShutdownPolicy
public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy()
Gets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown
. In this case, these tasks will only terminate uponshutdownNow
or after setting the policy tofalse
when already shutdown. This value is by defaultfalse
.- Returns:
true
if will continue after shutdown- See Also:
setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean)
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setExecuteExistingDelayedTasksAfterShutdownPolicy
public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)
Sets the policy on whether to execute existing delayed tasks even when this executor has beenshutdown
. In this case, these tasks will only terminate uponshutdownNow
, or after setting the policy tofalse
when already shutdown. This value is by defaulttrue
.- Parameters:
value
- iftrue
, execute after shutdown, else don't.- See Also:
getExecuteExistingDelayedTasksAfterShutdownPolicy()
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getExecuteExistingDelayedTasksAfterShutdownPolicy
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy()
Gets the policy on whether to execute existing delayed tasks even when this executor has beenshutdown
. In this case, these tasks will only terminate uponshutdownNow
, or after setting the policy tofalse
when already shutdown. This value is by defaulttrue
.- Returns:
true
if will execute after shutdown- See Also:
setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean)
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setRemoveOnCancelPolicy
public void setRemoveOnCancelPolicy(boolean value)
Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by defaultfalse
.- Parameters:
value
- iftrue
, remove on cancellation, else don't- Since:
- 1.7
- See Also:
getRemoveOnCancelPolicy()
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getRemoveOnCancelPolicy
public boolean getRemoveOnCancelPolicy()
Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by defaultfalse
.- Returns:
true
if cancelled tasks are immediately removed from the queue- Since:
- 1.7
- See Also:
setRemoveOnCancelPolicy(boolean)
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shutdown
public void 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.If the
ExecuteExistingDelayedTasksAfterShutdownPolicy
has been setfalse
, existing delayed tasks whose delays have not yet elapsed are cancelled. And unless theContinueExistingPeriodicTasksAfterShutdownPolicy
has been settrue
, future executions of existing periodic tasks will be cancelled.- Specified by:
shutdown
in interfaceExecutorService
- Overrides:
shutdown
in classThreadPoolExecutor
- Throws:
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 holdRuntimePermission
("modifyThread"), or the security manager's checkAccess method denies access.
-
shutdownNow
public 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.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.- Specified by:
shutdownNow
in interfaceExecutorService
- Overrides:
shutdownNow
in classThreadPoolExecutor
- Returns:
- list of tasks that never commenced execution.
Each element of this list is a
ScheduledFuture
, including those tasks submitted usingexecute
, which are for scheduling purposes used as the basis of a zero-delayScheduledFuture
. - Throws:
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 holdRuntimePermission
("modifyThread"), or the security manager's checkAccess method denies access.
-
getQueue
public BlockingQueue<Runnable> getQueue()
Returns the task queue used by this executor. Each element of this queue is aScheduledFuture
, including those tasks submitted usingexecute
which are for scheduling purposes used as the basis of a zero-delayScheduledFuture
. Iteration over this queue is not guaranteed to traverse tasks in the order in which they will execute.- Overrides:
getQueue
in classThreadPoolExecutor
- Returns:
- the task queue
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Nederlandse vertaling
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Bij voorbaat dank.
Document heeft de 11/06/2005 gemaakt, de laatste keer de 04/03/2020 gewijzigd
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