Propagate slf4j MDC (mapped diagnostic context) in rxjava Observables

Question

I'm using rxjava observables (v 1.1.8) in my play framework (with akka) application. I'd like to know if there's a way to propagate MDC info to rxjava Observables. I don't see MDC info in my log statements which get printed within Observable/Subscriber. I understand rxJava uses separate thread pool and there needs to be a mechanism to copy MDC info from akka threads into rxjava threads. Is there a solution for this ?

FYI,within akka actors I'm achieving MDC propagation using lightbends cinnamon plugin (http://developer.lightbend.com/docs/monitoring/latest/extensions/mdc.html)

May be this [hook example or repo](https://github.com/bmcstdio/rxjava-slf4j-mdc-hook) helps! — baris.aydinoz, Mar 31 '19 at 06:23

score 0 · Answer 1 · answered Jul 26 '17 at 19:17

As you see from the Cinnamon documentation at your link, the MDC is actually propagated with the message. There is no equivalent concept of identity in RxJava. On the other hand, you are free to define the scheduler being used for RxJava operations and binding the MDC to the thread controlled by that scheduler.

dkb · Answer 2 · 2020-07-21T10:30:03.597

Even though this thread is old and many would have migrated to RxJava2, but just in case someone wanted an implementation:

For RxJava1:

Source


//client class
public class DemoApplication {

  public static void main(String[] args) {
      MDCContextForSchedulerHook.init();
      // Above line should be before application run
      // rest of the code ....
  }

}


// WebHook class

import rx.functions.Action0;
import rx.plugins.RxJavaPlugins;
import rx.plugins.RxJavaSchedulersHook;

public class MDCContextForSchedulerHook extends RxJavaSchedulersHook {

    @Override
    public Action0 onSchedule(Action0 action) {
        return super.onSchedule(new WrappedAction0(action));
    }

    public static void init() {
        RxJavaPlugins.getInstance().registerSchedulersHook(new MDCContextSchedulerHook());
    }

    private static class WrappedAction0 implements Action0 {
        private final Action0 actual;
        private final MDCContext mdcContext;

        public WrappedAction0(Action0 actual) {
            this.actual = actual;
            this.mdcContext = MDCContext.save();
        }

        @Override
        public void call() {
            mdcContext.restore();
            actual.call();
        }
    }

}

For RXJava 2:

Refer this

Propagate slf4j MDC (mapped diagnostic context) in rxjava Observables

2 Answers2