Quarkus Scheduler - Immediate First Run

[The-Funk]

Description

I've been using the Quarkus Scheduler a lot to programmatically schedule and pause jobs. I've been toying around with building a runtime configuration provider, something similar to LaunchDarkly/Unleash. It's kind of a pet project and taking a lot of time, but one thing I was hoping to do is run all config pushes through the Quarkus scheduler.

When scheduling jobs via the imperative interface, one thing that would be nice is the ability to fire a job immediately upon registration of the trigger.

Implementation ideas

I'm not sure if there's a simple way to implement this but the desired interface, I imagine, would look something like this:

         scheduler.newJob("myJobId")
                .setInterval(Duration.ofSeconds(60))
                .setAsyncTask(executionContext -> myTask())
                .setFirstRunImmediate(true)
                .schedule();

If anyone has an idea on a decent way to implement this I'd be happy to offer a PR.

[quarkus-bot]

/cc @manovotn (scheduler), @mkouba (scheduler)

[manovotn]

That is an interesting idea.
Obviously, you then run a risk of triggering the operation twice in a quick succession but that seems like something you should count with when using this configuration. Or perhaps we could add a parameter for a grace period in which you don't want another retrigger, but that might get too convoluted with all the other knobs already in place.

I did not check much further but first thing coming to mind would be to tweak the Trigger implementations to include some initial trigger time (basically representing the moment of creation of such task) and then invocation of their evaluate(...) method would always return a time in order to trigger execution.

Here are some pointers:

• Here's a link to the SimpleTrigger class and its subclasses which implement evaluate() method
• These are triggered from ScheduledTask#execute(...)
• Which is in turn coming from SimpleScheduler#checkTriggers

@mkouba is sure to have some idea as well :)

[mkouba]

So if your task does not make use of the ScheduledExecution then simply call myTask() directly right after the registration? And if it's async and you register the task on a blocking thread then just use io.quarkus.vertx.VertxContextSupport#subscribeAndAwait(Supplier<Uni<T>>) to execute the job.

Honestly, I'm not quite sure this is a common use case that needs to be solved on the API level 🤷.