Allow Quarkus Scheduler to handle concurrent execution

[pcasaes]

Description
According to the docs Quarkus Scheduler allows concurrent execution

https://quarkus.io/guides/scheduler

The invocation of the scheduled method does not depend on the status or result of the previous invocation.

It would be nice to be able to prevent concurrent execution.

Implementation ideas

We can add a property to the Scheduled annotation that would control this. It would default to the concurrent behavior of course.

[gsmet]

/cc @mkouba

[mkouba]

Sounds reasonable. We could add concurrentExecution() default true to @Scheduled. For simple scheduler we'll add a mutable flag to the trigger. For Quartz this would be mapped to a job class annotated with org.quartz.DisallowConcurrentExecution.

[mkouba]

I've finished the implementation but I'm still struggling to write a proper test.

[mkouba]

Hm, actually the contract of @DisallowConcurrentExecution is a bit different compared to what I would expect. The job execution is not skipped but delayed until the previous job finished. That's a bit more complex to implement. We need to think about it...

[McIntozh]

Hi,
I postet a simmilar request some days ago, where, in a possible workaround, I received the wanted behaviour by adding the synchronized modifier to the scheduled method: #9883

[mkouba]

I've created a draft PR here: #10338

[mkouba]

@pcasaes @McIntozh does the aforementioned PR fix your problem?

[pcasaes]

Being able to SKIP is very much what I was looking for. Thank you!