It’s possible that it could be solved, sure, but RxJava is complex and has so many layers of objects that it’s very difficult to trace what’s going on. As was mentioned above, the difference between hot and cold subscriptions and how hard it is (at least it was for me) to know what runs on what thread, all of these issues made it incredibly difficult to work with and I don’t see these things going away as they’re caused by fundamental design choices.

It would be easier, in my opinion, to design something that is like Rx and has a very similar api or feature set, but is architected to avoid these issues. We ended up building a system from queues which supported many of the operations Rx did (map, filter, join, merge, etc). I will say that our implementation wasn’t super efficient in terms of thread usage (it creates more threads than really necessary), but that could have been solved, it just wasn’t necessary for our needs.