Schedulers in Project Reactor with Spring Webflux

Question

Project Reactor is awesome, easily I can switch a thread to processing some parts on another thread but I've looked inside to Schedulers.fromExecutorService() method, and this method every time allocates new ExecutorService. So when this method is called then always schedulers are creating and allocated again. I am not sure but I think it potential memory leak...


Mono<String> sometext() {
return Mono
.fromCallable(() -> "" )
.subscribeOn(Schedulers.newParallel("my-custom));
}

I wonder about registering Scheduler as bean, it singleton so only once will be allocated not every time or create him in the constructor. Many of the blogs explaining the threading model in this way.

...
private final Scheduler scheduler = Schedulers.newParallel("my-custom);
..
Mono.fromCallable(() -> "" ).subscribeOn(scheduler)

Michael Berry Michael Berry · Accepted Answer · 2021-05-10T15:53:12

Schedulers.newParallel() will indeed create a new scheduler with an associated backed threadpool every time you call it - so yes, you're correct, if you're using that method then you want to make sure you store a reference to it somewhere so you can reuse it. Simply providing the same name argument won't just retrieve the new scheduler, it'll just create a different one with the same name.

How you do this is up to you - it can be via a spring bean (as long as it's a singleton and not a prototype bean!), a field, or whatever else fits best in with your use case.

However, before all of this I'd first consider whether you definitely need to create a separate parallel scheduler at all. The Schedulers.parallel() scheduler is a default parallel scheduler that can be used for parallel work out the tin (it doesn't create a new one on each invocation), and unless you need separately configured parallel schedulers for separate services for some reason, best practice is just to use that.

Schedulers in Project Reactor with Spring Webflux

1 Answers