so apparently user of my program encounters deadlock issues rnadomly in my program, apparently in a area of the code where i use coroutines and channels but the worst is.. i cannot manage to reproduce it with the same input data on my hardware would i be able to use visualvm to see where it is blocking itself? i also did not quite rule out that ktor-client-cio is not at fault, but again no idea how to test that :thread-please:

Visiualvm won’t help you here. For local development we have a prototype of async stracktraces + jstack — https://github.com/Kotlin/kotlinx.coroutines/pull/572 But you have not so many options when you are already deadlocked. Akka, erlang and other reactive systems have similar problem: you can instrument everything to properly trace dependencies, but you cannot do it when problem already happened. I used to play with JVM serviceability API (openjdk only), but it’s far from complete: https://github.com/qwwdfsad/coroutines-dump-agent Maybe (I’m not yet sure) this agent can be a dynamic jstack analogue for coroutines

well i could log when entering / leaving a function, then visualize that and see where it got stuck just no clue which program could visualize that for me or maybe even solve it with annotations

But if you can log everything, maybe you can just run with debug agent enabled?