Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

How to remove a task from ScheduledExecutorService?

I have a ScheduledExecutorService that times a few different task periodically with scheduleAtFixedRate(Runnable, INIT_DELAY, ACTION_DELAY, TimeUnit.SECONDS);

I also have a different Runnable that I'm using with this scheduler. the problem starts when I want to remove one of the tasks from the scheduler.

Is there a way to do this?

Am I doing the right thing using one scheduler for different tasks? What is the best way to implement this?

like image 606
thepoosh Avatar asked Jan 20 '13 10:01

thepoosh


People also ask

Can we cancel a callable task?

You can cancel a future using Future. cancel() method. It attempts to cancel the execution of the task and returns true if it is cancelled successfully, otherwise, it returns false. The cancel() method accepts a boolean argument - mayInterruptIfRunning .

Which method can cancel the future task triggered by submit () of ExecutorService?

You can cancel the task submitted to ExecutorService by simply calling the cancel method on the future submitted when the task is submitted.


2 Answers

Simply cancel the future returned by scheduledAtFixedRate():

// Create the scheduler ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1); // Create the task to execute Runnable r = new Runnable() {     @Override     public void run() {         System.out.println("Hello");     } }; // Schedule the task such that it will be executed every second ScheduledFuture<?> scheduledFuture =     scheduledExecutorService.scheduleAtFixedRate(r, 1L, 1L, TimeUnit.SECONDS); // Wait 5 seconds Thread.sleep(5000L); // Cancel the task scheduledFuture.cancel(false); 

Another thing to note is that cancel does not remove the task from scheduler. All it ensures is that isDone method always return true. This may lead to memory leaks if you keep adding such tasks. For e.g.: if you start a task based on some client activity or UI button click, repeat it n-times and exit. If that button is clicked too many times, you might end up with big pool of threads that cannot be garbage collected as scheduler still has a reference.

You may want to use setRemoveOnCancelPolicy(true) in ScheduledThreadPoolExecutor class available in Java 7 onwards. For backward compatibility, default is set to false.

like image 92
JB Nizet Avatar answered Oct 06 '22 00:10

JB Nizet


If your ScheduledExecutorService instance extends ThreadPoolExecutor (e.g. ScheduledThreadPoolExecutor), you could use remove(Runnable) (but see the note in its javadoc: "It may fail to remove tasks that have been converted into other forms before being placed on the internal queue.") or purge().

like image 35
Gary Avatar answered Oct 06 '22 00:10

Gary