|
FlexDoc/Javadoc 2.0 Demo Java Doc |
Delayed tasks execute no sooner than they are enabled, but without any real-time guarantees about when, after they are enabled, they will commence. Tasks scheduled for exactly the same execution time are enabled in first-in-first-out (FIFO) order of submission.
When a submitted task is cancelled before it is run, execution is suppressed. By default, such a cancelled task is not automatically removed from the work queue until its delay elapses. While this enables further inspection and monitoring, it may also cause unbounded retention of cancelled tasks. To avoid this, use setRemoveOnCancelPolicy(boolean) to cause tasks to be immediately removed from the work queue at time of cancellation.
Successive executions of a periodic task scheduled via 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.
}
Nested Class Summary |
Nested classes/interfaces inherited from class java.util.concurrent.ThreadPoolExecutor |
Constructor Summary |
||
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 |
||
Modifies or replaces the task used to execute a callable.
|
||
Modifies or replaces the task used to execute a runnable.
|
||
void |
Executes command with zero required delay.
|
|
boolean |
Gets the policy on whether to continue executing existing
periodic tasks even when this executor has been shutdown.
|
|
boolean |
Gets the policy on whether to execute existing delayed
tasks even when this executor has been shutdown.
|
|
getQueue()
Returns the task queue used by this executor.
|
||
boolean |
Gets the policy on whether cancelled tasks should be immediately
removed from the work queue at time of cancellation.
|
|
Submits a value-returning one-shot task that becomes enabled
after the given delay.
|
||
Submits a one-shot task that becomes enabled after the given delay.
|
||
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.
|
||
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.
|
|
Attempts to stop all actively executing tasks, halts the
processing of waiting tasks, and returns a list of the tasks
that were awaiting execution.
|
||
Submits a value-returning task for execution and returns a
Future representing the pending results of the task.
|
||
Future<?> |
Submits a Runnable task for execution and returns a Future
representing that task.
|
|
Submits a Runnable task for execution and returns a Future
representing that task.
|
Methods inherited from class java.util.concurrent.AbstractExecutorService |
Methods inherited from class java.lang.Object |
public ScheduledThreadPoolExecutor |
(int corePoolSize) |
public ScheduledThreadPoolExecutor |
(int corePoolSize, ThreadFactory threadFactory) |
public ScheduledThreadPoolExecutor |
(int corePoolSize, RejectedExecutionHandler handler) |
public ScheduledThreadPoolExecutor |
public ScheduledFuture<?> schedule |
public ScheduledFuture<?> scheduleAtFixedRate |
The sequence of task executions continues indefinitely until one of the following exceptional completions occur:
If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.
public ScheduledFuture<?> scheduleWithFixedDelay |
The sequence of task executions continues indefinitely until one of the following exceptional completions occur:
public void execute |
(Runnable command) |
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().
public Future<?> submit |
(Runnable 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.
public void setContinueExistingPeriodicTasksAfterShutdownPolicy |
(boolean value) |
public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy |
() |
public void setExecuteExistingDelayedTasksAfterShutdownPolicy |
(boolean value) |
public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy |
() |
public void setRemoveOnCancelPolicy |
(boolean value) |
public boolean getRemoveOnCancelPolicy |
() |
public void shutdown |
() |
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.
() |
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.
() |
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.
|
FlexDoc/Javadoc 2.0 Demo Java Doc |