[ ghc-Bugs-1187295 ] runProcess hangs with duplicate handles

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Bugs item #1187295, was opened at 2005-04-21 11:11
Message generated for change (Settings changed) made by simonpj
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Category: libraries/base
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Roman Leshchinskiy (romanle)
>Assigned to: Simon Marlow (simonmar)
Summary: runProcess hangs with duplicate handles

Initial Comment:
runProcess doesn't seem to allow the same handle to be
used for redirecting stdout and stderr. Thus,

main = 
  do
    h  <- openFile "output" WriteMode
    ph <- runProcess "/bin/ls" [] Nothing Nothing
               Nothing (Just h) (Just h)
    waitForProcess ph
    return ()

hangs in ghci and aborts with "thread blocked
indefinitely" if compiled.   This isn't documented and
I hope this is not the intended behaviour as
redirecting stdout and stderr (and stdin in the case of
ptys) to the same file/pipe is quite common.

System is Linux 2.4.20-8 #1 Thu Mar 13 17:54:28 EST
2003 i686
ghc is vanilla 6.4

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