Ghosts of Unix past, part 3: Unfixable designs

Please do bring this up with the kernel hackers. We were thinking of using signalfd in the GHC runtime / IO system until we discovered this problem with having to block all signals in all threads which makes it unusable (it's not just child processes, libraries can make their own threads). We have to stick with the approach of installing a signal hander that writes to a pipe (or we can use eventfd for the cases where there is no data associated with the signal).