fromEmitter same-pool deadlock

[akarnokd]

This affects both 1.x and 2.x.

There is a question on StackOverflow where the example program hangs after it delivered the default bufferSize elements until the fromEmitter source completes.

The problem is that subscribeOn schedules the downstream's replenishing request on the same thread that is busy/sleeping and has no opportunity to update its internal requested amount. We had similar problems with onBackpressureBlock which had to be dropped.

We could introduce a subscribeOn mode in which it doesn't reschedule the request from downstream but it will confuse some and make wonder others.

[akarnokd]

This was resolved in 2.x by making sure a subscribeOn after create doesn't reschedule downstream requests.

[bobvanderlinden]

I think I'm running into this problem as well. fromEmitter suddenly stops emitting onNext items whereas the emitter itself is still being called.

I was using a single-thread-scheduler for the emitter, so I thought (from your explanation) that moving to a threadpool would resolve the problem. It apparently does not for my case. I'm probably misunderstanding what is going on behind the scenes.

Do you have any suggestions on how to workaround this issue (without moving to 2.x).

[akarnokd]

@bobvanderlinden Yes, use the NONE policy and apply onBackpressureXXX after subscribeOn.

[bobvanderlinden]

@akarnokd That works like a charm! Thanks a lot!

[akarnokd]

Closing via #5091 for 1.x and #4770 for 2.x.