CODEWITHSUNDEEP
javamultithreadingscheduledexecutorservice
mystarrocks
mystarrocks

Reputation: 4088

Maintaining a single executor service and shutting it down appropriately

My application requires that a certain job be done asynchronously, so I've resorted to the executor framework. This job (a Runnable) is expected to be run should a certain external interface be down (the vendor could be backed up for a while, say, 30 mins).

With this ask in mind, I believe I should maintain a single scheduled executor service with a fixed no. of core threads that perform these jobs when the interface I said above goes down for a brief moment (as a static variable in the class I need the thread pool in). I also don't think I should create an executor for every need to handle such a job (single scheduled thread pool executor), and shut down after a job is run, because that would defeat my purpose, wouldn't it? Because that could mean reserving a thread for every job during the backed up hour which sounds scary to me.

But, if I were to maintain such a single executor service, when would I be shutting down the executor? I understand that an executor once shut down can't be reused, while not shutting down the executor and keeping threads active could prevent the JVM from shutting down. How do I go about this?

My last statement was based on this from Effective Java 2nd edition:

And here is how to tell the executor to terminate gracefully (if you fail to do this, it is likely that your VM will not exit):

executor.shutdown();

Upvotes: 0

Views: 765

Answers (1)

hagrawal7777
hagrawal7777

Reputation: 14658

This job (a Runnable) is expected to be run should a certain external interface be down (the vendor could be backed up for a while, say, 30 mins).

Above is your requirement. Now the solution entirely depends on how above situation is handled.

  • Trigger or event listener: If you have some trigger or event listener which can be called when it is found that a certain external interface is down, then in the that triggered code or event listener, you can create a ExecutorService, execute all your tasks (you can choose on fixed or pooled thread pool), and then on completion of all tasks, you can shutdown the ExecutorService
    In this case, it is a good idea to create a ExecutorService, do tasks and shut it down. No need of long running ExecutorService.

  • Track or periodic check: If you have to track or check periodically whether certain external interface is down or not, then I think you can have a ScheduledThreadPoolExecutor implementation to have check after fixed time interval whether certain external interface is down or not, and if it is down then execute all your tasks. In this case you will NOT shutdown your ExecutorService and it will always be running.

P.S.: Trigger and Track are my own convention I used tangentially as one word, so do infer it in technical words.

I understand that an executor once shut down can't be reused, while not shutting down the executor and keeping threads active could prevent the JVM from shutting down.

Yes, an executor once shut down can't be reused.
No, a running ExecutorService will not stop you JVM shutdown, but once JVM is shutdown that ExecutorService instance and its thread pool will be stopped and destroyed.

Upvotes: 2

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