Added in API level 1

Summary: Ctors | Methods | Protected Methods | Inherited Methods

ScheduledThreadPoolExecutor

public class ScheduledThreadPoolExecutor
extends ThreadPoolExecutor implements ScheduledExecutorService

java.lang.Object
↳	java.util.concurrent.AbstractExecutorService
	↳	java.util.concurrent.ThreadPoolExecutor
		↳	java.util.concurrent.ScheduledThreadPoolExecutor

---

A ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable to Timer when multiple worker threads are needed, or when the additional flexibility or capabilities of ThreadPoolExecutor (which this class extends) are required.

Delayed tasks execute no sooner than they are enabled, but without any real-time guarantees about when, after they are enabled, they will commence. Tasks scheduled for exactly the same execution time are enabled in first-in-first-out (FIFO) order of submission.

When a submitted task is cancelled before it is run, execution is suppressed. By default, such a cancelled task is not automatically removed from the work queue until its delay elapses. While this enables further inspection and monitoring, it may also cause unbounded retention of cancelled tasks.

Successive executions of a periodic task scheduled via scheduleAtFixedRate or scheduleWithFixedDelay do not overlap. While different executions may be performed by different threads, the effects of prior executions happen-before those of subsequent ones.

While this class inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect. Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.

As with ThreadPoolExecutor, if not otherwise specified, this class uses Executors#defaultThreadFactory as the default thread factory, and ThreadPoolExecutor.AbortPolicy as the default rejected execution handler.

Extension notes: This class overrides the execute and submit methods to generate internal ScheduledFuture objects to control per-task delays and scheduling. To preserve functionality, any further overrides of these methods in subclasses must invoke superclass versions, which effectively disables additional task customization. However, this class provides alternative protected extension method decorateTask (one version each for Runnable and Callable) that can be used to customize the concrete task types used to execute commands entered via execute, submit, schedule, scheduleAtFixedRate, and scheduleWithFixedDelay. By default, a ScheduledThreadPoolExecutor uses a task type extending FutureTask. However, this may be modified or replaced using subclasses of the form:

 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.
 }

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) 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.
<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<?>	schedule(Runnable command, long delay, TimeUnit unit) Submits a 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 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 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(Callable<T> task) Submits a value-returning task for execution and returns a Future representing the pending results of the task.
<T> Future<T>	submit(Runnable task, T result) Submits a Runnable task for execution and returns a Future representing that task.

Protected methods
<V> RunnableScheduledFuture<V>	decorateTask(Runnable runnable, RunnableScheduledFuture<V> task) Modifies or replaces the task used to execute a runnable.
<V> RunnableScheduledFuture<V>	decorateTask(Callable<V> callable, RunnableScheduledFuture<V> task) Modifies or replaces the task used to execute a callable.

Inherited methods
From class java.util.concurrent.ThreadPoolExecutor 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) void beforeExecute(Thread t, Runnable r) Method invoked prior to executing the given Runnable in the given thread. void execute(Runnable command) Executes the given task sometime in the future. void finalize() This method is deprecated. Subclass is not recommended to override finalize(). If it must, please always invoke super.finalize(). 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. BlockingQueue<Runnable> getQueue() Returns the task queue used by this executor. 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() boolean isTerminated() boolean isTerminating() Returns true if this executor is in the process of terminating after shutdown() or 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. 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. 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.
From class java.util.concurrent.AbstractExecutorService <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. <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) Returns a RunnableFuture for the given runnable and default value. <T> RunnableFuture<T> newTaskFor(Callable<T> callable) Returns a RunnableFuture for the given callable 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. <T> Future<T> submit(Runnable task, T result) Submits a Runnable task for execution and returns a Future representing that task. Future<?> submit(Runnable task) Submits a Runnable task for execution and returns a Future representing that task.
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the 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. String toString() Returns a string representation of the object. 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. 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() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
From interface java.util.concurrent.ExecutorService abstract 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. abstract <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. abstract <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. abstract <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. abstract <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. abstract boolean isShutdown() Returns true if this executor has been shut down. abstract boolean isTerminated() Returns true if all tasks have completed following shut down. abstract void shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. abstract 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. abstract <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. abstract <T> Future<T> submit(Runnable task, T result) Submits a Runnable task for execution and returns a Future representing that task. abstract Future<?> submit(Runnable task) Submits a Runnable task for execution and returns a Future representing that task.
From interface java.util.concurrent.ScheduledExecutorService abstract <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. abstract ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) Submits a one-shot task that becomes enabled after the given delay. abstract 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 after initialDelay, then initialDelay + period, then initialDelay + 2 * period, and so on. abstract 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.
From interface java.util.concurrent.Executor abstract void execute(Runnable command) Executes the given command at some time in the future.

Public constructors

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize)

Creates a new ScheduledThreadPoolExecutor with the given core pool size.

Parameters
corePoolSize	int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set

Throws
IllegalArgumentException	if corePoolSize < 0

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                ThreadFactory threadFactory)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
corePoolSize	int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set
threadFactory	ThreadFactory: the factory to use when the executor creates a new thread

Throws
IllegalArgumentException	if corePoolSize < 0
NullPointerException	if threadFactory is null

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                RejectedExecutionHandler handler)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
corePoolSize	int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set
handler	RejectedExecutionHandler: the handler to use when execution is blocked because the thread bounds and queue capacities are reached

Throws
IllegalArgumentException	if corePoolSize < 0
NullPointerException	if handler is null

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                ThreadFactory threadFactory, 
                RejectedExecutionHandler handler)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
corePoolSize	int: the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set
threadFactory	ThreadFactory: the factory to use when the executor creates a new thread
handler	RejectedExecutionHandler: the handler to use when execution is blocked because the thread bounds and queue capacities are reached

Throws
IllegalArgumentException	if corePoolSize < 0
NullPointerException	if threadFactory or handler is null

Public methods

execute

Added in API level 1

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.

Parameters
command	Runnable: 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

getContinueExistingPeriodicTasksAfterShutdownPolicy

Added in API level 1

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
boolean	true if will continue after shutdown

See also:

• setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean)

getExecuteExistingDelayedTasksAfterShutdownPolicy

Added in API level 1

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
boolean	true if will execute after shutdown

See also:

• setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean)

getQueue

Added in API level 1

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.

Returns
BlockingQueue<Runnable>	the task queue

getRemoveOnCancelPolicy

Added in API level 21

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
boolean	true if cancelled tasks are immediately removed from the queue

See also:

• setRemoveOnCancelPolicy(boolean)

schedule

Added in API level 1

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

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

Parameters
callable	Callable: the function to execute
delay	long: the time from now to delay execution
unit	TimeUnit: the time unit of the delay parameter

Returns
ScheduledFuture<V>	a ScheduledFuture that can be used to extract result or cancel

Throws
RejectedExecutionException
NullPointerException

schedule

Added in API level 1

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

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

Parameters
command	Runnable: the task to execute
delay	long: the time from now to delay execution
unit	TimeUnit: the time unit of the delay parameter

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion

Throws
RejectedExecutionException
NullPointerException

scheduleAtFixedRate

Added in API level 1

public 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 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.

Parameters
command	Runnable: the task to execute
initialDelay	long: the time to delay first execution
period	long: the period between successive executions
unit	TimeUnit: the time unit of the initialDelay and period parameters

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's get() method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
RejectedExecutionException
NullPointerException
IllegalArgumentException

scheduleWithFixedDelay

Added in API level 1

public 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 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.

Parameters
command	Runnable: the task to execute
initialDelay	long: the time to delay first execution
delay	long: the delay between the termination of one execution and the commencement of the next
unit	TimeUnit: the time unit of the initialDelay and delay parameters

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's get() method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
RejectedExecutionException
NullPointerException
IllegalArgumentException

setContinueExistingPeriodicTasksAfterShutdownPolicy

Added in API level 1

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	boolean: if true, continue after shutdown, else don't

See also:

• getContinueExistingPeriodicTasksAfterShutdownPolicy()

setExecuteExistingDelayedTasksAfterShutdownPolicy

Added in API level 1

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	boolean: if true, execute after shutdown, else don't

See also:

• getExecuteExistingDelayedTasksAfterShutdownPolicy()

setRemoveOnCancelPolicy

Added in API level 21

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	boolean: if true, remove on cancellation, else don't

See also:

• getRemoveOnCancelPolicy()

shutdown

Added in API level 1

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.

shutdownNow

Added in API level 1

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.

Returns
List<Runnable>	list of tasks that never commenced execution. Each element of this list is a ScheduledFuture. For tasks submitted via one of the schedule methods, the element will be identical to the returned ScheduledFuture. For tasks submitted using execute, the element will be a zero-delay ScheduledFuture.

submit

Added in API level 1

public Future<?> submit (Runnable task)

Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return null upon successful completion.

Parameters
task	Runnable: the task to submit

Returns
Future<?>	a Future representing pending completion of the task

Throws
RejectedExecutionException
NullPointerException

submit

Added in API level 1

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. 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.

Parameters
task	Callable: the task to submit

Returns
Future<T>	a Future representing pending completion of the task

Throws
RejectedExecutionException
NullPointerException

submit

Added in API level 1

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

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.

Parameters
task	Runnable: the task to submit
result	T: the result to return

Returns
Future<T>	a Future representing pending completion of the task

Throws
RejectedExecutionException
NullPointerException

Protected methods

decorateTask

Added in API level 9

protected 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	Runnable: the submitted Runnable
task	RunnableScheduledFuture: the task created to execute the runnable

Returns
RunnableScheduledFuture<V>	a task that can execute the runnable

decorateTask

Added in API level 9

protected 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	Callable: the submitted Callable
task	RunnableScheduledFuture: the task created to execute the callable

Returns
RunnableScheduledFuture<V>	a task that can execute the callable