[Matthias247]

It's not easy to cancel any future. It's easy to *pretend* to cancel any future. E.g. if you cancel (drop) anything that uses spawn_blocking, it will just continue to run in the background without you being aware of it. If you cancel any async fs operation that is implemented in terms of a threadpool, it will also continue to run.

This all can lead to very hard to understand bugs - e.g. "why does my service fail because a file is still in use, while I'm sure nothing uses the file anymore"

[pornel]

Yes, if you have a blocking thread running then you have to use the classic threaded methods for cancelling it, like periodically checking a boolean. This can compose nicely with Futures if they flip the boolean on Drop.

I’ve also used custom executors that can tolerate long-blocking code in async, and then an occasional yield.await can cancel compute-bound code.