Date: Thu, 10 Sep 1998 07:50:18 +0100 From: Mark Ovens <marko@uk.radan.com> To: Brian Somers <brian@Awfulhak.org> Cc: questions@FreeBSD.ORG, freebsd-users@freebsd-uk.eu.org Subject: Re: Help needed with fork(), pipe() & dup2() Message-ID: <35F776AA.9A256020@uk.radan.com> References: <199809100136.CAA05582@woof.lan.awfulhak.org>
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Brian Somers wrote:
>
> [.....]
> > while (gets (line) != NULL)
> > {
> > .
> > .
> > code to process "line" here
> > .
> > .
> > }
> >
> > close (fd [0]);
> ^^^^^^^^^^^^^^^
> Dodgy - fd[0] has already been closed (unless == STDIN_FILENO).
>
> > } /* parent */
> > else
> > { /* child */
> > close (fd [0]);
> > if (fd [1] != STDOUT_FILENO)
> > {
> > dup2(fd [1], STDOUT_FILENO)
> > close (fd [1]);
> > }
> > if (execvp ("file", files) < 0)
> > error_message ();
> > close (fd [1]);
>
> Ditto, but this one (hopefully) doesn't normally happen. You're also
> missing an exit() here.
I did wonder about that. I tried commenting out the close() calls but
it made no difference. I'll try adding exit()
>
> > } /* child */
> > }
>
> I don't know enough about the rest of the code to tell if that first
> close may be the problem - but it *might*. Also, are you sure that
> last error_message() isn't being called ?
Definitely. It's an X program and the error_message function pops up a
message window, and that definitely isn't happening.
I got another reply suggesting that the problem is caused by the code
assuming the order in which the parent & child execute, i.e. the
parent reads the pipe (and sees NULL) before the child has written to
it. This seems a very likely possiblity.
>
> --
> Brian <brian@Awfulhak.org>, <brian@FreeBSD.org>, <brian@OpenBSD.org>
> <http://www.Awfulhak.org>;
> Don't _EVER_ lose your sense of humour....
--
When everything's coming your way, you're in the wrong lane.
Mark Ovens, CNC Applications Engineer, Radan Computational Ltd
Sheet Metal CAD/CAM Solutions
mailto:marko@uk.radan.com http://www.radan.com
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