System.Process bugs on Unix
jgoerzen at complete.org
Thu Mar 29 06:52:53 EDT 2007
On Thu, Mar 29, 2007 at 10:55:43AM +0100, Simon Marlow wrote:
> Bryan O'Sullivan wrote:
> >John Goerzen wrote:
> >>And strace shows that, sure enough, read(0,...) in grep is getting
> >>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"
See fcntl(2) -- F_SETFL can change the O_NONBLOCK flag. I don't think
this should be a problem for the RTS since it can be done only on the
endpoint of the pipe that is used post-fork.
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