quoth Karsten Gebbert, ...
My questions are these: is there anything I need to take care of when handling sub-processes like this, specifically while writing to stdin of the process, and with particular regard to -threaded? Does anybody spot a problem or something I'm overlooking when handling processes like this?
I can't say I know what's going wrong. One thing you can do when using handles on a pipe, is put "hFlush hand" after your "hPutStr hand" - that will clean up problems with buffering. Really a process level buffered I/O layer like this is very little help for your application, and adds various complexities. If you're interested, you might extract the process handles' POSIX file descriptors and use those - System.Posix.IO handleToFd, fdWrite, etc. - just as an experiment. I don't see how the problems you report really suggest that you have a buffering problem that would naturally be cured by this, though. The other generic red flag here, for -threaded, is that the threaded runtime uses POSIX signals to dispatch certain background functions. That creates a flood of signal handling interrupts that can disrupt library functions. To find out if that's a problem, you may turn that off, on the command line +RTS -V0 -RTS. Donn