If pipes to and from your sub-process are giving you so much pain under mod_perl, is there a reason why you don't just put the input in a file and run ghostscript so it reads from that file and puts the output in another?

To get the thing running, I'm just doing one command (generate this page image), but eventually, yes, I'll be initializing a Ghostscript for a particular document, then coming back to it later to say, OK, now give me a page image for page 5. OK, I'm back, give me page 6. Me again, page 7 please.

Eventually I'll have a hash holding pointers to waiting Ghostscript processes (one for each document) and some intelligence that goes around and says, "OK, you've waited long enough without anything to do, away you go." I can't go that until I can get IPC::Run figured out.

Are you trying to keep a ghostscript process running over the long-term, handling multiple requests, or something like that?

Yes.