Bryan O'Sullivan wrote:
John Goerzen wrote:
And strace shows that, sure enough, read(0,...) in grep is getting EAGAIN.
Sounds like somebody forgot to take the fd out of non-blocking mode.
Yep, that looks like what's happening. See System/Process/Internals.hs:runProcessPosix. I wonder why the lower-level runProcess that it calls is written in C.
We can't just take a file descriptor out of non-blocking mode, because due to broken POSIX semantics that would screw up GHC's use of the file descriptor (there's no way to set non-blocking mode per-FD). We can "fix" this by modifying the IO library to work with FDs in blocking mode, which is possible in the threaded RTS, but we haven't completed this yet, see http://hackage.haskell.org/trac/ghc/ticket/724 I've just milestoned this bug for 6.6.2, so I promise to at least try to fix it before then... Cheers, Simon