- java.lang.Object
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- 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 AThreadPoolExecutorthat can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable toTimerwhen 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, use setRemoveOnCancelPolicy(boolean)to cause tasks to be immediately removed from the work queue at time of cancellation.Successive executions of a periodic task scheduled via scheduleAtFixedRateorscheduleWithFixedDelaydo 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 usingcorePoolSizethreads and an unbounded queue, adjustments tomaximumPoolSizehave no useful effect. Additionally, it is almost never a good idea to setcorePoolSizeto zero or useallowCoreThreadTimeOutbecause 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 usesExecutors.defaultThreadFactory()as the default thread factory, andThreadPoolExecutor.AbortPolicyas the default rejected execution handler.Extension notes: This class overrides the executeandsubmitmethods to generate internalScheduledFutureobjects 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 forRunnableandCallable) that can be used to customize the concrete task types used to execute commands entered viaexecute,submit,schedule,scheduleAtFixedRate, andscheduleWithFixedDelay. By default, aScheduledThreadPoolExecutoruses 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 declared in class java.util.concurrent.ThreadPoolExecutorThreadPoolExecutor.AbortPolicy, ThreadPoolExecutor.CallerRunsPolicy, ThreadPoolExecutor.DiscardOldestPolicy, ThreadPoolExecutor.DiscardPolicy
 
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Constructor SummaryConstructors Constructor Description ScheduledThreadPoolExecutor(int corePoolSize)Creates a newScheduledThreadPoolExecutorwith the given core pool size.ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description protected <V> RunnableScheduledFuture<V>decorateTask(Runnable runnable, RunnableScheduledFuture<V> task)Modifies or replaces the task used to execute a runnable.protected <V> RunnableScheduledFuture<V>decorateTask(Callable<V> callable, RunnableScheduledFuture<V> task)Modifies or replaces the task used to execute a callable.voidexecute(Runnable command)Executescommandwith zero required delay.booleangetContinueExistingPeriodicTasksAfterShutdownPolicy()Gets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown.booleangetExecuteExistingDelayedTasksAfterShutdownPolicy()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.booleangetRemoveOnCancelPolicy()Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation.ScheduledFuture<?>schedule(Runnable command, long delay, TimeUnit unit)Submits a one-shot task that becomes enabled after the given delay.<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.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 afterinitialDelay, theninitialDelay + period, theninitialDelay + 2 * period, and so on.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.voidsetContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value)Sets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown.voidsetExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)Sets the policy on whether to execute existing delayed tasks even when this executor has beenshutdown.voidsetRemoveOnCancelPolicy(boolean value)Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation.voidshutdown()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.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.<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.- 
Methods declared in class java.util.concurrent.ThreadPoolExecutorafterExecute, allowCoreThreadTimeOut, allowsCoreThreadTimeOut, beforeExecute, finalize, getActiveCount, getCompletedTaskCount, getCorePoolSize, getKeepAliveTime, getLargestPoolSize, getMaximumPoolSize, getPoolSize, getRejectedExecutionHandler, getTaskCount, getThreadFactory, isTerminating, prestartAllCoreThreads, prestartCoreThread, purge, remove, setCorePoolSize, setKeepAliveTime, setMaximumPoolSize, setRejectedExecutionHandler, setThreadFactory, terminated, toString
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Methods declared in class java.util.concurrent.AbstractExecutorServicenewTaskFor, newTaskFor
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Methods declared in class java.lang.Objectclone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.concurrent.ExecutorServiceawaitTermination, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminated
 
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Constructor Detail- 
ScheduledThreadPoolExecutorpublic ScheduledThreadPoolExecutor(int corePoolSize) Creates a newScheduledThreadPoolExecutorwith the given core pool size.- Parameters:
- corePoolSize- the number of threads to keep in the pool, even if they are idle, unless- allowCoreThreadTimeOutis set
- Throws:
- IllegalArgumentException- if- corePoolSize < 0
 
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ScheduledThreadPoolExecutorpublic ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.- Parameters:
- corePoolSize- the number of threads to keep in the pool, even if they are idle, unless- allowCoreThreadTimeOutis set
- threadFactory- the factory to use when the executor creates a new thread
- Throws:
- IllegalArgumentException- if- corePoolSize < 0
- NullPointerException- if- threadFactoryis null
 
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ScheduledThreadPoolExecutorpublic ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.- Parameters:
- corePoolSize- the number of threads to keep in the pool, even if they are idle, unless- allowCoreThreadTimeOutis set
- handler- the handler to use when execution is blocked because the thread bounds and queue capacities are reached
- Throws:
- IllegalArgumentException- if- corePoolSize < 0
- NullPointerException- if- handleris null
 
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ScheduledThreadPoolExecutorpublic ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler)Creates a newScheduledThreadPoolExecutorwith the given initial parameters.- Parameters:
- corePoolSize- the number of threads to keep in the pool, even if they are idle, unless- allowCoreThreadTimeOutis set
- threadFactory- the factory to use when the executor creates a new thread
- handler- the handler to use when execution is blocked because the thread bounds and queue capacities are reached
- Throws:
- IllegalArgumentException- if- corePoolSize < 0
- NullPointerException- if- threadFactoryor- handleris null
 
 
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Method Detail- 
decorateTaskprotected <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.- Type Parameters:
- V- the type of the task's result
- Parameters:
- runnable- the submitted Runnable
- task- the task created to execute the runnable
- Returns:
- a task that can execute the runnable
- Since:
- 1.6
 
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decorateTaskprotected <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.- Type Parameters:
- V- the type of the task's result
- Parameters:
- callable- the submitted Callable
- task- the task created to execute the callable
- Returns:
- a task that can execute the callable
- Since:
- 1.6
 
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schedulepublic ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) Description copied from interface:ScheduledExecutorServiceSubmits a one-shot task that becomes enabled after the given delay.- Specified by:
- schedulein interface- ScheduledExecutorService
- Parameters:
- command- the task to execute
- delay- the time from now to delay execution
- unit- the time unit of the delay parameter
- Returns:
- a ScheduledFuture representing pending completion of
         the task and whose get()method will returnnullupon completion
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if command or unit is null
 
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schedulepublic <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) Description copied from interface:ScheduledExecutorServiceSubmits a value-returning one-shot task that becomes enabled after the given delay.- Specified by:
- schedulein interface- ScheduledExecutorService
- Type Parameters:
- V- the type of the callable's result
- Parameters:
- callable- the function to execute
- delay- the time from now to delay execution
- unit- 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 execution
- NullPointerException- if callable or unit is null
 
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scheduleAtFixedRatepublic 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 afterinitialDelay, theninitialDelay + period, theninitialDelay + 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 whether to continue after shutdown 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 geton the returned future will throwExecutionException, holding the exception as its cause.
 isDone()on the returned future will returntrue.If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute. - Specified by:
- scheduleAtFixedRatein interface- ScheduledExecutorService
- Parameters:
- command- the task to execute
- initialDelay- the time to delay first execution
- period- the period between successive executions
- unit- the time unit of the initialDelay and period parameters
- Returns:
- 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.
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if command or unit is null
- IllegalArgumentException- if period less than or equal to zero
 
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scheduleWithFixedDelaypublic 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.
- Method shutdown()is called and the policy on whether to continue after shutdown 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 geton the returned future will throwExecutionException, holding the exception as its cause.
 isDone()on the returned future will returntrue.- Specified by:
- scheduleWithFixedDelayin interface- ScheduledExecutorService
- Parameters:
- command- the task to execute
- initialDelay- the time to delay first execution
- delay- the delay between the termination of one execution and the commencement of the next
- unit- the time unit of the initialDelay and delay parameters
- Returns:
- 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.
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if command or unit is null
- IllegalArgumentException- if delay less than or equal to zero
 
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executepublic void execute(Runnable command) Executescommandwith zero required delay. This has effect equivalent toschedule(command, 0, anyUnit). Note that inspections of the queue and of the list returned byshutdownNowwill access the zero-delayedScheduledFuture, not thecommanditself.A consequence of the use of ScheduledFutureobjects is thatafterExecuteis always called with a null secondThrowableargument, even if thecommandterminated abruptly. Instead, theThrowablethrown by such a task can be obtained viaFuture.get().- Specified by:
- executein interface- Executor
- Overrides:
- executein class- ThreadPoolExecutor
- Parameters:
- command- the task to execute
- Throws:
- RejectedExecutionException- at discretion of- RejectedExecutionHandler, if the task cannot be accepted for execution because the executor has been shut down
- NullPointerException- if- commandis null
 
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submitpublic Future<?> submit(Runnable task) Description copied from interface:ExecutorServiceSubmits a Runnable task for execution and returns a Future representing that task. The Future'sgetmethod will returnnullupon successful completion.- Specified by:
- submitin interface- ExecutorService
- Overrides:
- submitin class- AbstractExecutorService
- Parameters:
- task- the task to submit
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
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submitpublic <T> Future<T> submit(Runnable task, T result) Description copied from interface:ExecutorServiceSubmits a Runnable task for execution and returns a Future representing that task. The Future'sgetmethod will return the given result upon successful completion.- Specified by:
- submitin interface- ExecutorService
- Overrides:
- submitin class- AbstractExecutorService
- Type Parameters:
- T- the type of the result
- Parameters:
- task- the task to submit
- result- the result to return
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
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submitpublic <T> Future<T> submit(Callable<T> task) Description copied from interface:ExecutorServiceSubmits a value-returning task for execution and returns a Future representing the pending results of the task. The Future'sgetmethod 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 Executorsclass includes a set of methods that can convert some other common closure-like objects, for example,PrivilegedActiontoCallableform so they can be submitted.- Specified by:
- submitin interface- ExecutorService
- Overrides:
- submitin class- AbstractExecutorService
- Type Parameters:
- T- the type of the task's result
- Parameters:
- task- the task to submit
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
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setContinueExistingPeriodicTasksAfterShutdownPolicypublic void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value) Sets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown. In this case, executions will continue untilshutdownNowor the policy is set tofalsewhen already shutdown. This value is by defaultfalse.- Parameters:
- value- if- true, continue after shutdown, else don't
- See Also:
- getContinueExistingPeriodicTasksAfterShutdownPolicy()
 
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getContinueExistingPeriodicTasksAfterShutdownPolicypublic boolean getContinueExistingPeriodicTasksAfterShutdownPolicy() Gets the policy on whether to continue executing existing periodic tasks even when this executor has beenshutdown. In this case, executions will continue untilshutdownNowor the policy is set tofalsewhen already shutdown. This value is by defaultfalse.- Returns:
- trueif will continue after shutdown
- See Also:
- setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean)
 
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setExecuteExistingDelayedTasksAfterShutdownPolicypublic 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 tofalsewhen already shutdown. This value is by defaulttrue.- Parameters:
- value- if- true, execute after shutdown, else don't
- See Also:
- getExecuteExistingDelayedTasksAfterShutdownPolicy()
 
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getExecuteExistingDelayedTasksAfterShutdownPolicypublic 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 tofalsewhen already shutdown. This value is by defaulttrue.- Returns:
- trueif will execute after shutdown
- See Also:
- setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean)
 
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setRemoveOnCancelPolicypublic 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- if- true, remove on cancellation, else don't
- Since:
- 1.7
- See Also:
- getRemoveOnCancelPolicy()
 
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getRemoveOnCancelPolicypublic 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:
- trueif cancelled tasks are immediately removed from the queue
- Since:
- 1.7
- See Also:
- setRemoveOnCancelPolicy(boolean)
 
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shutdownpublic 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 awaitTerminationto do that.If the ExecuteExistingDelayedTasksAfterShutdownPolicyhas been setfalse, existing delayed tasks whose delays have not yet elapsed are cancelled. And unless theContinueExistingPeriodicTasksAfterShutdownPolicyhas been settrue, future executions of existing periodic tasks will be cancelled.- Specified by:
- shutdownin interface- ExecutorService
- Overrides:
- shutdownin class- ThreadPoolExecutor
- 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 hold- RuntimePermission- ("modifyThread"), or the security manager's- checkAccessmethod denies access.
 
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shutdownNowpublic 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. 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 awaitTerminationto 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.- Specified by:
- shutdownNowin interface- ExecutorService
- Overrides:
- shutdownNowin class- ThreadPoolExecutor
- Returns:
- list of tasks that never commenced execution.
         Each element of this list is a ScheduledFuture. For tasks submitted via one of theschedulemethods, the element will be identical to the returnedScheduledFuture. For tasks submitted usingexecute, the element will be 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 hold- RuntimePermission- ("modifyThread"), or the security manager's- checkAccessmethod denies access.
 
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getQueuepublic BlockingQueue<Runnable> getQueue() 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 theschedulemethods, the element will be identical to the returnedScheduledFuture. For tasks submitted usingexecute, the element will be a zero-delayScheduledFuture.Iteration over this queue is not guaranteed to traverse tasks in the order in which they will execute. - Overrides:
- getQueuein class- ThreadPoolExecutor
- Returns:
- the task queue
 
 
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