Re: emacs-22.x hang in child after forking a process (before exec)

Re: emacs-22.x hang in child after forking a process (before exec)

[Chong Yidong]

> We noticed that we can not build auctex on Tru64 Unix 5.1
> (alphaev67-dec-osf5.1) because emacs-22.2 hangs. It also hangs with, for
> example "M-! ls". This all works fine on the same machine with
> emacs-21.4 (and also hangs with emacs-22.1)
>
> Any ideas on what changed from 21.x to 22.x that could be causing this?

I'm afraid there were significant changes in process control between
Emacs 21 and 22.  I don't know any Emacs developers who use Tru64 Unix,
and the bug doesn't seem to occur on GNU/Linux.  Would it be possible
for you to try to debug this?  Does the hang occur at the call to
setpgrp() in callproc.c, as indicated by the backtrace you sent?  There
are several different versions of the call to setpgrp for different
platforms; which one does Tru64 Unix use?

Re: emacs-22.x hang in child after forking a process (before exec)

[Peter O'Gorman]

On Mon, May 26, 2008 at 11:55:29PM -0400, Chong Yidong wrote:
> > We noticed that we can not build auctex on Tru64 Unix 5.1
> > (alphaev67-dec-osf5.1) because emacs-22.2 hangs. It also hangs with, for
> > example "M-! ls". This all works fine on the same machine with
> > emacs-21.4 (and also hangs with emacs-22.1)
> >
> > Any ideas on what changed from 21.x to 22.x that could be causing this?
> 
> I'm afraid there were significant changes in process control between
> Emacs 21 and 22.  I don't know any Emacs developers who use Tru64 Unix,
> and the bug doesn't seem to occur on GNU/Linux.  Would it be possible
> for you to try to debug this?  Does the hang occur at the call to
> setpgrp() in callproc.c, as indicated by the backtrace you sent?  There
> are several different versions of the call to setpgrp for different
> platforms; which one does Tru64 Unix use?

Hi,

Ok, it turned out to be rather simple to fix. When we build with the
gtk+ frontend, emacs is a multithreaded process. Tru64 seems to have
issues with vfork and what gets called after vfork in a multithreaded
process. The simple fix was to export ac_cv_func_vfork=no before
configuring emacs, so that it will use fork to spawn a subprocess.

There is no issue when emacs is built with the lucid front end or
without X11 support. We did not see the issue with emacs-21.x because we
did not build that with gtk+ support.

Sorry for the noise,
Peter
-- 
Peter O'Gorman
pogma@thewrittenword.com