non blocking System.system?

I was curious if there was a version of System.system floating about which doesn't block all threads when doing concurrency? just doing an actual fork and exec isn't sufficient because I need to do haskell things (like write to MVars) after the spawned app finishes. I imagine this might be written by catching sigCHLD and writing to an mvar, but I can't seem to get at the siginfo_t structure from the haskell signal callback to find out the pid of the process which died. John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john@foo.net ---------------------------------------------------------------------------