Re: Blocking a task indefinitely in the RTS

Okay, I skimmed rts/Schedule.c and now see the problem you mentioned :(

On the non-threaded runtime the timeslice case doesn't apply and you only have one capability, it will force a GC to try to revive some tasks, and if at the end of this the tasks are still blocked it will release one in order to attempt to proceed. In short, as far as I can tell I don't think it considers reach-ability at all, not for MVars.

Maybe that should be considered a false positive (bug) for the deadlock checker? Just because the Haskell runtime has a single thread, that doesn't imply the whole program is necessarily single-threaded (in the presence of foreign things). I'd think this is a legitimate use case for MVars.