Timer is creating multiple timer instances

Question

This a real simple issue I guess but I am not able to figure why it happens so though. I have an implementation of an EJB timer which uses @Singleton annotation i.e. a singleton timer. I have set it to run after every 5 mins. The code looks something like this : ``` @Singleton @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED) public class Scheduler { private static final double timerVar = Math.random() * 33; static Logger logger = Logger.getLogger("Scheduler"); @Schedule(second = "*", minute = "*/5", hour = "*", persistent = true) public void doWork() { logger.log(Level.INFO, "timer value for this session : " + timerVar); } } ``` When the process runs it executed 10 scheduler instances simultaneously in a gap of 1 sec i.e. ``` (EJB default - 1) (EJB default - 2) (EJB default - 3) (EJB default - 4) ``` and so on. When I put a lengthy operation within the code, the `(EJB default - 1)` is not complete and when `(EJB default - 2)` tries to execute it gives me an error saying:…

Accepted Answer

First, how can I avoid multiple EJB scheduler instances to be executed at a time?

You are creating persistent timers. So after specified interval, it will be creating new ones & enqueueing them, waiting for the previous one to finish its execution.

I presume, after you restart, all enqueued timers have timed-out & multiple instances will be created by the server as they are persistent.

Second, what is the deal with "could not obtain lock within 5000MILLISECONDS" and how can I avoid it?

It's singleton, all method have lock-type write by default, so only one thread will be executiing at a time. Therefore others will get timeout exception/ could not obtain lock etc. as you said, there is a long running process.

Timer is creating multiple timer instances

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