Equivalent of PublishOn, SubscribeOn, Work-Stealing/Drain-loop, Scheduler - Controlling which thread callback runs on

[hutchig]

When looking at the issue of multiple Subscribers a topic that came up was
a nested

onNext(
   onNext(
      onNext(

stack.

Problem: As onNext cannot be called more than once there is only one data payload traversing the stream.

However the 'obvious' solution is for onNext to return early having kicked off
some concurrent work on a different thread to complete a CompletionStage when
done.

A downside of this is that a payload will switch threads as it moves through each
onData layer (as onNext has to return the calling thread to the caller).

See https://youtu.be/hfupNIxzNP4?t=1872 for intro.

To get the best of both worlds we need the ability to influence the thread used
for the processing of a stage.

I am not sure what milestone this is best done for but wanted a place (here) to discuss.

[cescoffier]

It depends on your execution model. Using an event loop model will always go back to the same context, avoiding the switch.