waitForProcess: does not exist (No child processes)

I have this error when launching a program on our REHL prod machine.

waitForProcess: does not exist (No child processes)

This is called inside readProcess. I am unable to reproduce it on our REHL dev machine, and my local Ubuntu machine. If I re-implement readProcess with the same source but remove waitForProcess line, I do get standard output. Launching the program is successful.

The problem stems from waitForProcess expecting a process and somehow there isn't one. I didn't think this would be a problem, because waitForProcess itself doesn't throw such an exception, and it *does* handle the process having ended (of course), which is trivial to confirm locally:

λ> (inh,outh,_,pid) <- createProcess (proc "date" [])
Tue May 24 11:19:59 CEST 2011
λ> waitForProcess pid
ExitSuccess
λ>

So perhaps it's in withProcessHandle, which I don't have access to in the Haddock docs. I don't really know what would cause this error. Ideas?

We're using GHC 6.12.3 (I know, not recent). I'd provide a test-case but I can't even reproduce it on my own machine. I don't have direct shell access to the prod machine. The test-case would essentially be "use readProcess", anyway.

I can assign this to me and I'll see if the problem persists when we upgrade to GHC7. FWIW if you want to reproduce the exact case I tried, here it is:

readProcess "pdfinfo" ["--help"] ""

$ pdfinfo -v
pdfinfo version 3.00
Copyright 1996-2004 Glyph & Cog, LLC

Trac metadata

Trac field	Value
Version	6.12.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHC API
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture