| 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(Runnable, long, long, TimeUnit) or
scheduleWithFixedDelay(Runnable, long, long, TimeUnit) 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.
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 CustomTaskprotectedimplements RunnableScheduledFuture { ... RunnableScheduledFuture decorateTask( Runnable r, RunnableScheduledFuture task) { return new CustomTask (r, task); } protected RunnableScheduledFuture decorateTask( Callable c, RunnableScheduledFuture task) { return new CustomTask (c, task); } // ... add constructors, etc. }}
| Public Constructors | |||||||||||
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Creates a new
ScheduledThreadPoolExecutor with the
given core pool size.
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Creates a new
ScheduledThreadPoolExecutor with the
given initial parameters.
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Creates a new
ScheduledThreadPoolExecutor with the
given initial parameters.
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Creates a new
ScheduledThreadPoolExecutor with the
given initial parameters.
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| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Executes
command with zero required delay.
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Gets the policy on whether to continue executing existing
periodic tasks even when this executor has been
shutdown.
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Gets the policy on whether to execute existing delayed
tasks even when this executor has been
shutdown.
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Returns the task queue used by this executor.
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Gets the policy on whether cancelled tasks should be immediately
removed from the work queue at time of cancellation.
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Creates and executes a one-shot action that becomes enabled
after the given delay.
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Creates and executes a ScheduledFuture that becomes enabled after the
given delay.
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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.
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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.
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Sets the policy on whether to continue executing existing
periodic tasks even when this executor has been
shutdown.
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Sets the policy on whether to execute existing delayed
tasks even when this executor has been
shutdown.
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Sets the policy on whether cancelled tasks should be immediately
removed from the work queue at time of cancellation.
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Initiates an orderly shutdown in which previously submitted
tasks are executed, but no new tasks will be accepted.
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Attempts to stop all actively executing tasks, halts the
processing of waiting tasks, and returns a list of the tasks
that were awaiting execution.
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Submits a Runnable task for execution and returns a Future
representing that task.
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Submits a value-returning task for execution and returns a
Future representing the pending results of the task.
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Submits a Runnable task for execution and returns a Future
representing that task.
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| Protected Methods | |||||||||||
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Modifies or replaces the task used to execute a runnable.
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Modifies or replaces the task used to execute a callable.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.util.concurrent.ThreadPoolExecutor
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From class
java.util.concurrent.AbstractExecutorService
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From class
java.lang.Object
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From interface
java.util.concurrent.ExecutorService
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From interface
java.util.concurrent.ScheduledExecutorService
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From interface
java.util.concurrent.Executor
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Creates a new ScheduledThreadPoolExecutor with the
given core pool size.
| corePoolSize | the number of threads to keep in the pool, even
if they are idle, unless allowCoreThreadTimeOut is set |
|---|
| IllegalArgumentException | if corePoolSize < 0
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|---|
Creates a new ScheduledThreadPoolExecutor with the
given initial 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 |
| IllegalArgumentException | if corePoolSize < 0 |
|---|---|
| NullPointerException | if threadFactory is null
|
Creates a new ScheduledThreadPoolExecutor with the
given initial 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 |
| IllegalArgumentException | if corePoolSize < 0 |
|---|---|
| NullPointerException | if handler is null
|
Creates a new ScheduledThreadPoolExecutor with the
given initial 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 |
| IllegalArgumentException | if corePoolSize < 0 |
|---|---|
| NullPointerException | if threadFactory or
handler is null
|
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 get().
| command | the task to execute |
|---|
| RejectedExecutionException | at discretion of
RejectedExecutionHandler, if the task
cannot be accepted for execution because the
executor has been shut down |
|---|---|
| NullPointerException |
Gets 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.
Developers
true if will continue after shutdownGets 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.
true if will execute after shutdownReturns the task queue used by this executor.
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(Runnable), 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.
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.
true if cancelled tasks are immediately removed
from the queueCreates and executes a one-shot action that becomes enabled after the given delay.
| command | the task to execute |
|---|---|
| delay | the time from now to delay execution |
| unit | the time unit of the delay parameter |
get() method will return
null upon completionCreates and executes a ScheduledFuture that becomes enabled after the given delay.
| callable | the function to execute |
|---|---|
| delay | the time from now to delay execution |
| unit | the time unit of the delay parameter |
Creates and executes a periodic action that becomes enabled first
after the given initial delay, and subsequently with the given
period; that is executions will commence after
initialDelay then initialDelay+period, then
initialDelay + 2 * period, and so on.
If any execution of the task
encounters an exception, subsequent executions are suppressed.
Otherwise, the task will only terminate via cancellation or
termination of the executor. If any execution of this task
takes longer than its period, then subsequent executions
may start late, but will not concurrently execute.
| 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 |
get() method will throw an
exception upon cancellationCreates 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.
| 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 |
get() method will throw an
exception upon cancellationSets 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.
| value | if true, continue after shutdown, else don't |
|---|
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.
| value | if true, execute after shutdown, else don't |
|---|
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.
| value | if true, remove on cancellation, else don't |
|---|
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.
Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
This method does not wait for actively executing tasks to
terminate. Use awaitTermination to
do that.
There are no guarantees beyond best-effort attempts to stop
processing actively executing tasks. This implementation
cancels tasks via interrupt(), so any task that
fails to respond to interrupts may never terminate.
ScheduledFuture.
For tasks submitted via one of the schedule
methods, the element will be identical to the returned
ScheduledFuture. For tasks submitted using
execute(Runnable), the element will be a zero-delay ScheduledFuture.
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.
| task | the task to submit |
|---|---|
| result | the result to return |
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.
| task | the task to submit |
|---|
Submits a Runnable task for execution and returns a Future
representing that task. The Future's get method will
return null upon successful completion.
| task | the task to submit |
|---|
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.
| runnable | the submitted Runnable |
|---|---|
| task | the task created to execute the runnable |
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.
| callable | the submitted Callable |
|---|---|
| task | the task created to execute the callable |