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Re: Cygwin Subprocesses on XEmacs

On Jan 28 08:20, Vin Shelton wrote:
> Hi, Corinna et al,
> On Wed, Jan 28, 2015 at 4:53 AM, Corinna Vinschen wrote:
> > On Jan 27 23:05, Vin Shelton wrote:
> >> I spent some time debugging M-x shell in XEmacs on 32-bit Cygwin.
> >> Here's what I found out.
> >>
> >> In the child after fork() but before exec(), the setsid() call in
> >> disconnect_controlling_terminal() is causing the subprocess not to
> >> function after it gets spawned.
> >
> > Can you define "not function" a bit more detailed?  Does no process work
> > at all, or do only processes requiring a tty not work?  For instance,
> > does something like an "echo foo > bar" still work?
> M-x shell is specifically designed to spawn an interactive process
> like a shell.  The bash subprocess starts, but it accepts no input.
> Here is the output of ps for that process:
> S    1740     252    1740        268  pty1    1003 08:10:54 /usr/bin/bash
> I think it's only commands requiring a tty, but that's the whole point
> of M-x shell mode.  There is a separate command - M-x shell-command -
> which is designed to run and capture the output of individual commands
> like "ls" or "echo".  That works fine.
> BTW, if I try to spawn gdb as a shell, the behavior is similar, but
> this time the process looks like this:
>      3328    3248    3328       3408  pty2    1003 08:15:18
> /usr/bin/gdb <defunct>
> HTH.
> >>
> >> Thanks for any insight you can offer.
> >
> > Hmm, not off the top of my head.  Is there a chance that you could
> > provide a simple, self contained testcase to reproduce the setsid
> > behaviour?  I think I have to debug that.
> You mean a simpler test case than XEmacs?  That seems like a low bar.  :-)


Btw., a testcase which avoids to fork would be nice.  It's much easier
to debug due to GDBs inability to follow fork on Cygwin :(

> I'll try.  Meanwhile, I've been looking at the emacs code (which in
> this case is simpler) to see if I can figure out how it is that M-x
> shell works there.

Good idea.  This might give us a clue.


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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