Class ScheduledThreadPoolExecutor

java.util.concurrent.ScheduledThreadPoolExecutor

All Implemented Interfaces:: AutoCloseable, Executor, ExecutorService, ScheduledExecutorService

public class ScheduledThreadPoolExecutor extends ThreadPoolExecutor implements ScheduledExecutorService

A 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 for execution, 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 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:

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

Nested Class Summary

Nested classes/interfaces declared in class ThreadPoolExecutor

ThreadPoolExecutor.AbortPolicy, ThreadPoolExecutor.CallerRunsPolicy, ThreadPoolExecutor.DiscardOldestPolicy, ThreadPoolExecutor.DiscardPolicy

Modifier and Type	Class	Description
`static class`	`ThreadPoolExecutor.AbortPolicy`	A handler for rejected tasks that throws a `RejectedExecutionException`.
`static class`	`ThreadPoolExecutor.CallerRunsPolicy`	A handler for rejected tasks that runs the rejected task directly in the calling thread of the `execute` method, unless the executor has been shut down, in which case the task is discarded.
`static class`	`ThreadPoolExecutor.DiscardOldestPolicy`	A handler for rejected tasks that discards the oldest unhandled request and then retries `execute`, unless the executor is shut down, in which case the task is discarded.
`static class`	`ThreadPoolExecutor.DiscardPolicy`	A handler for rejected tasks that silently discards the rejected task.

Constructor Summary

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.

Method Summary

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.
`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.
`ScheduledFuture<?>`	`schedule(Runnable command, long delay, TimeUnit unit)`	Submits a one-shot task that becomes enabled for execution 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 for execution after the given delay.
`ScheduledFuture<?>`	`scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)`	Submits a periodic action that becomes enabled for execution 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)`	Submits a periodic action that becomes enabled for execution 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.
`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 ThreadPoolExecutor

afterExecute, allowCoreThreadTimeOut, allowsCoreThreadTimeOut, awaitTermination, beforeExecute, getActiveCount, getCompletedTaskCount, getCorePoolSize, getKeepAliveTime, getLargestPoolSize, getMaximumPoolSize, getPoolSize, getRejectedExecutionHandler, getTaskCount, getThreadFactory, isShutdown, isTerminated, isTerminating, prestartAllCoreThreads, prestartCoreThread, purge, remove, setCorePoolSize, setKeepAliveTime, setMaximumPoolSize, setRejectedExecutionHandler, setThreadFactory, terminated, toString

Modifier and Type	Method	Description
`protected void`	`afterExecute(Runnable r, Throwable t)`	Method invoked upon completion of execution of the given Runnable.
`void`	`allowCoreThreadTimeOut(boolean value)`	Sets the policy governing whether core threads may time out and terminate if no tasks arrive within the keep-alive time, being replaced if needed when new tasks arrive.
`boolean`	`allowsCoreThreadTimeOut()`	Returns true if this pool allows core threads to time out and terminate if no tasks arrive within the keepAlive time, being replaced if needed when new tasks arrive.
`boolean`	`awaitTermination(long timeout, TimeUnit unit)`	Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
`protected void`	`beforeExecute(Thread t, Runnable r)`	Method invoked prior to executing the given Runnable in the given thread.
`int`	`getActiveCount()`	Returns the approximate number of threads that are actively executing tasks.
`long`	`getCompletedTaskCount()`	Returns the approximate total number of tasks that have completed execution.
`int`	`getCorePoolSize()`	Returns the core number of threads.
`long`	`getKeepAliveTime(TimeUnit unit)`	Returns the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.
`int`	`getLargestPoolSize()`	Returns the largest number of threads that have ever simultaneously been in the pool.
`int`	`getMaximumPoolSize()`	Returns the maximum allowed number of threads.
`int`	`getPoolSize()`	Returns the current number of threads in the pool.
`RejectedExecutionHandler`	`getRejectedExecutionHandler()`	Returns the current handler for unexecutable tasks.
`long`	`getTaskCount()`	Returns the approximate total number of tasks that have ever been scheduled for execution.
`ThreadFactory`	`getThreadFactory()`	Returns the thread factory used to create new threads.
`boolean`	`isShutdown()`	Returns `true` if this executor has been shut down.
`boolean`	`isTerminated()`	Returns `true` if all tasks have completed following shut down.
`boolean`	`isTerminating()`	Returns true if this executor is in the process of terminating after `ThreadPoolExecutor.shutdown()` or `ThreadPoolExecutor.shutdownNow()` but has not completely terminated.
`int`	`prestartAllCoreThreads()`	Starts all core threads, causing them to idly wait for work.
`boolean`	`prestartCoreThread()`	Starts a core thread, causing it to idly wait for work.
`void`	`purge()`	Tries to remove from the work queue all `Future` tasks that have been cancelled.
`boolean`	`remove(Runnable task)`	Removes this task from the executor's internal queue if it is present, thus causing it not to be run if it has not already started.
`void`	`setCorePoolSize(int corePoolSize)`	Sets the core number of threads.
`void`	`setKeepAliveTime(long time, TimeUnit unit)`	Sets the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.
`void`	`setMaximumPoolSize(int maximumPoolSize)`	Sets the maximum allowed number of threads.
`void`	`setRejectedExecutionHandler(RejectedExecutionHandler handler)`	Sets a new handler for unexecutable tasks.
`void`	`setThreadFactory(ThreadFactory threadFactory)`	Sets the thread factory used to create new threads.
`protected void`	`terminated()`	Method invoked when the Executor has terminated.
`String`	`toString()`	Returns a string identifying this pool, as well as its state, including indications of run state and estimated worker and task counts.

Methods declared in class AbstractExecutorService

invokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskFor

Modifier and Type	Method	Description
`<T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks)`	Executes the given tasks, returning a list of Futures holding their status and results when all complete.
`<T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)`	Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
`<T> T`	`invokeAny(Collection<? extends Callable<T>> tasks)`	Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
`<T> T`	`invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)`	Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
`protected <T> RunnableFuture<T>`	`newTaskFor(Runnable runnable, T value)`	Returns a `RunnableFuture` for the given runnable and default value.
`protected <T> RunnableFuture<T>`	`newTaskFor(Callable<T> callable)`	Returns a `RunnableFuture` for the given callable task.

Methods declared in class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Methods declared in interface ExecutorService

close

Modifier and Type	Method	Description
`default void`	`close()`	Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.

Constructor Details

ScheduledThreadPoolExecutor

public ScheduledThreadPoolExecutor(int corePoolSize)

Creates a new ScheduledThreadPoolExecutor with the given core pool size.

Parameters:: corePoolSize - the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set
Throws:: IllegalArgumentException - if corePoolSize < 0

ScheduledThreadPoolExecutor

public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)

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, unless allowCoreThreadTimeOut is set; threadFactory - the factory to use when the executor creates a new thread
Throws:: IllegalArgumentException - if corePoolSize < 0; NullPointerException - if threadFactory is null

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, unless allowCoreThreadTimeOut is 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 handler is null

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, unless allowCoreThreadTimeOut is 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 threadFactory or handler is null

Method Details

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.

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

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.

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

schedule

public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)

Description copied from interface: ScheduledExecutorService

Submits a one-shot task that becomes enabled for execution after the given delay.

Specified by:: schedule in 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 return null upon completion
Throws:: RejectedExecutionException - if the task cannot be scheduled for execution; NullPointerException - if command or unit is null

schedule

public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)

Description copied from interface: ScheduledExecutorService

Submits a value-returning one-shot task that becomes enabled for execution after the given delay.

Specified by:: schedule in 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

scheduleAtFixedRate

public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)

Submits a periodic action that becomes enabled for execution 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 whether to continue after shutdown is not set true, or method shutdownNow() 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 throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.

Specified by:: scheduleAtFixedRate in 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

scheduleWithFixedDelay

public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)

Submits a periodic action that becomes enabled for execution 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 method shutdownNow() 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 throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

Specified by:: scheduleWithFixedDelay in 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

execute

public void execute(Runnable command)

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 Future.get().

Specified by:: execute in interface Executor
Overrides:: execute in 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 command is null

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 interface ExecutorService
Overrides:: submit in 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

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 interface ExecutorService
Overrides:: submit in 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

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 to Callable form so they can be submitted.

Specified by:: submit in interface ExecutorService
Overrides:: submit in 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

setContinueExistingPeriodicTasksAfterShutdownPolicy

public void setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value)

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:

value - if true, continue after shutdown, else don't

See Also:

getContinueExistingPeriodicTasksAfterShutdownPolicy

public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy()

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.

Returns:

true if will continue after shutdown

See Also:

setExecuteExistingDelayedTasksAfterShutdownPolicy

public void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)

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:

value - if true, execute after shutdown, else don't

See Also:

getExecuteExistingDelayedTasksAfterShutdownPolicy

public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy()

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.

Returns:

true if will execute after shutdown

See Also:

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 default false.

Parameters:

value - if true, remove on cancellation, else don't

Since:

1.7

See Also:

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 default false.

Returns:

true if cancelled tasks are immediately removed from the queue

Since:

1.7

See Also:

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 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.

Specified by:: shutdown in interface ExecutorService
Overrides:: shutdown in class ThreadPoolExecutor

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. 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.

Specified by:: shutdownNow in interface ExecutorService
Overrides:: shutdownNow in class ThreadPoolExecutor
Returns:: 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.

getQueue

public 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 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.

Overrides:: getQueue in class ThreadPoolExecutor
Returns:: the task queue

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