public class

ScheduledThreadPoolExecutor

extends ThreadPoolExecutor
implements ScheduledExecutorService
java.lang.Object
   ↳ java.util.concurrent.AbstractExecutorService
     ↳ java.util.concurrent.ThreadPoolExecutor
       ↳ java.util.concurrent.ScheduledThreadPoolExecutor

Class Overview

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, 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.

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.

Summary

Public Constructors
ScheduledThreadPoolExecutor(int corePoolSize)
Creates a new ScheduledThreadPoolExecutor with the given core pool size.
ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)
Creates a new ScheduledThreadPoolExecutor with the given initial parameters.
ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler)
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.
Public Methods
void execute(Runnable command)
Execute command with zero required delay.
boolean getContinueExistingPeriodicTasksAfterShutdownPolicy()
Get the policy on whether to continue executing existing periodic tasks even when this executor has been shutdown.
boolean getExecuteExistingDelayedTasksAfterShutdownPolicy()
Get 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 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.
ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
Creates and executes a one-shot action that becomes enabled after the given delay.
<V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
Creates and executes a ScheduledFuture 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)
Set policy on whether to continue executing existing periodic tasks even when this executor has been shutdown.
void setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)
Set policy on whether to execute existing delayed tasks even when this executor has been shutdown.
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(Runnable task, T result)
Submits a Runnable task for execution and returns a Future representing that task that will upon completion return the given result
<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.
[Expand]
Inherited Methods
From class java.util.concurrent.ThreadPoolExecutor
From class java.util.concurrent.AbstractExecutorService
From class java.lang.Object
From interface java.util.concurrent.Executor
From interface java.util.concurrent.ExecutorService
From interface java.util.concurrent.ScheduledExecutorService

Public Constructors

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.
Throws
IllegalArgumentException if corePoolSize less than or equal to zero

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.
threadFactory the factory to use when the executor creates a new thread.
Throws
NullPointerException if threadFactory is null

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.
handler the handler to use when execution is blocked because the thread bounds and queue capacities are reached.
Throws
NullPointerException if handler is null

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.
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
NullPointerException if threadFactory or handler is null

Public Methods

public void execute (Runnable command)

Execute 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.

Parameters
command the task to execute
Throws
RejectedExecutionException at discretion of RejectedExecutionHandler, if task cannot be accepted for execution because the executor has been shut down.
NullPointerException if command is null

public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy ()

Get the policy on whether to continue executing existing periodic 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 false.

Returns
  • true if will continue after shutdown.
See Also

public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy ()

Get 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

public BlockingQueue<Runnable> getQueue ()

Returns the task queue used by this executor. Each element of this queue is a ScheduledFuture, including those tasks submitted using execute which are for scheduling purposes used as the basis of a zero-delay ScheduledFuture. Iteration over this queue is not guaranteed to traverse tasks in the order in which they will execute.

Returns
  • the task queue

public 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.

This method may be useful as one part of a cancellation scheme. It may fail to remove tasks that have been converted into other forms before being placed on the internal queue. For example, a task entered using submit might be converted into a form that maintains Future status. However, in such cases, method purge() may be used to remove those Futures that have been cancelled.

Parameters
task the task to remove
Returns
  • true if the task was removed

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

Creates and executes a one-shot action that becomes enabled after the given delay.

Parameters
command the task to execute.
delay the time from now to delay execution.
unit the time unit of the delay parameter.
Returns
  • a Future representing pending completion of the task, and whose get() method will return null upon completion.

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

Creates and executes a ScheduledFuture that becomes enabled after the given delay.

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.

public 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. 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.

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 Future representing pending completion of the task, and whose get() method will throw an exception upon cancellation.

public 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. 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.

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 Future representing pending completion of the task, and whose get() method will throw an exception upon cancellation.

public void setContinueExistingPeriodicTasksAfterShutdownPolicy (boolean value)

Set policy on whether to continue executing existing periodic 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 false.

Parameters
value if true, continue after shutdown, else don't.
See Also

public void setExecuteExistingDelayedTasksAfterShutdownPolicy (boolean value)

Set 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

public void shutdown ()

Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. 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.

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.

There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. This implementation cancels tasks via interrupt(), so if any tasks mask or fail to respond to interrupts, they may never terminate.

Returns
  • list of tasks that never commenced execution. Each element of this list is a ScheduledFuture, including those tasks submitted using execute, which are for scheduling purposes used as the basis of a zero-delay ScheduledFuture.

public Future<T> submit (Runnable task, T result)

Submits a Runnable task for execution and returns a Future representing that task that will upon completion return the given result

Parameters
task the task to submit
result the result to return
Returns
  • a Future representing pending completion of the task, and whose get() method will return the given result upon completion.

public Future<T> submit (Callable<T> task)

Submits a value-returning task for execution and returns a Future representing the pending results of the task.

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.

Parameters
task the task to submit
Returns
  • a Future representing pending completion of the task

public Future<?> submit (Runnable task)

Submits a Runnable task for execution and returns a Future representing that task.

Parameters
task the task to submit
Returns
  • a Future representing pending completion of the task, and whose get() method will return null upon completion.