jdk.util.concurrent.ScheduledThreadPoolExecutor — clojure-interop/java.util.concurrent 1.0.5

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. To avoid this, set setRemoveOnCancelPolicy(boolean) to true, which causes tasks to be immediately removed from the work queue at time of cancellation.

Successive executions of a 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.

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. }

->scheduled-thread-pool-executor clj

(->scheduled-thread-pool-executor core-pool-size)

(->scheduled-thread-pool-executor core-pool-size thread-factory)

(->scheduled-thread-pool-executor core-pool-size thread-factory handler)

Constructor.

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

core-pool-size - the number of threads to keep in the pool, even if they are idle, unless allowCoreThreadTimeOut is set - int thread-factory - the factory to use when the executor creates a new thread - java.util.concurrent.ThreadFactory handler - the handler to use when execution is blocked because the thread bounds and queue capacities are reached - java.util.concurrent.RejectedExecutionHandler

throws: java.lang.IllegalArgumentException - if corePoolSize < 0

execute clj

(execute this 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().

command - the task to execute - java.lang.Runnable

throws: java.util.concurrent.RejectedExecutionException - at discretion of RejectedExecutionHandler, if the task cannot be accepted for execution because the executor has been shut down

get-continue-existing-periodic-tasks-after-shutdown-policy? clj

(get-continue-existing-periodic-tasks-after-shutdown-policy? this)

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.

returns: true if will continue after shutdown - boolean

get-execute-existing-delayed-tasks-after-shutdown-policy? clj

(get-execute-existing-delayed-tasks-after-shutdown-policy? this)

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 - boolean

get-queue clj

(get-queue this)

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 - java.util.concurrent.BlockingQueue<java.lang.Runnable>

get-remove-on-cancel-policy? clj

(get-remove-on-cancel-policy? this)

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 - boolean

schedule clj

(schedule this command delay unit)

Description copied from interface: ScheduledExecutorService

command - the task to execute - java.lang.Runnable delay - the time from now to delay execution - long unit - the time unit of the delay parameter - java.util.concurrent.TimeUnit

returns: a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion - java.util.concurrent.ScheduledFuture<?>

throws: java.util.concurrent.RejectedExecutionException - if the task cannot be scheduled for execution

schedule-at-fixed-rate clj

(schedule-at-fixed-rate this command initial-delay period unit)

Description copied from interface: ScheduledExecutorService

command - the task to execute - java.lang.Runnable initial-delay - the time to delay first execution - long period - the period between successive executions - long unit - the time unit of the initialDelay and period parameters - java.util.concurrent.TimeUnit

returns: a ScheduledFuture representing pending completion of the task, and whose get() method will throw an exception upon cancellation - java.util.concurrent.ScheduledFuture<?>

throws: java.util.concurrent.RejectedExecutionException - if the task cannot be scheduled for execution

schedule-with-fixed-delay clj

(schedule-with-fixed-delay this command initial-delay delay unit)

Description copied from interface: ScheduledExecutorService

command - the task to execute - java.lang.Runnable initial-delay - the time to delay first execution - long delay - the delay between the termination of one execution and the commencement of the next - long unit - the time unit of the initialDelay and delay parameters - java.util.concurrent.TimeUnit

returns: a ScheduledFuture representing pending completion of the task, and whose get() method will throw an exception upon cancellation - java.util.concurrent.ScheduledFuture<?>

throws: java.util.concurrent.RejectedExecutionException - if the task cannot be scheduled for execution

set-continue-existing-periodic-tasks-after-shutdown-policy clj

(set-continue-existing-periodic-tasks-after-shutdown-policy this value)

Sets 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 - boolean

set-execute-existing-delayed-tasks-after-shutdown-policy clj

(set-execute-existing-delayed-tasks-after-shutdown-policy this 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.

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

set-remove-on-cancel-policy clj

(set-remove-on-cancel-policy this 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.

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

shutdown clj

(shutdown this)

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.

throws: java.lang.SecurityException - if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold RuntimePermission("modifyThread"), or the security manager's checkAccess method denies access.

shutdown-now clj

(shutdown-now this)

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 Thread.interrupt(), so any task that fails to respond to interrupts 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. - java.util.List<java.lang.Runnable>

throws: java.lang.SecurityException - if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold RuntimePermission("modifyThread"), or the security manager's checkAccess method denies access.

submit clj

(submit this task)

(submit this task result)

Description copied from interface: ExecutorService

task - the task to submit - java.lang.Runnable result - the result to return - T

returns: a Future representing pending completion of the task - <T> java.util.concurrent.Future<T>

throws: java.util.concurrent.RejectedExecutionException - if the task cannot be scheduled for execution