Re: FreeBSD compatability feature request

[Peter Stephenson <pws@xxxxxxx>]

Vincent Stemen wrote:
> After replacing /bin/sh with zsh, it was able to fully boot up and
> initialize the system except for one other problem, which appears to be a
> different bug in sh emulation mode.  It hangs when running the nfsd init
> script.  If I <cntl>c out of it, the rest of the system comes up, but
> without NFS.
> 
> I finally isolated the problem.  Below is a small script, called t, that
> reproduces it.
> 
> # cat t
> 
> _find_processes()
> {
>     ps | while read pid command
>     do
>         echo "pid=$pid  $command"
>     done >&2
> 
>     echo "xxx Exited loop xxxxxxxxxxxxxxxxxxxxxxx" >&2
> }
> 
> xxx=$(_find_processes)
> 
> #--- end of script -------

Making a link to sh from zsh and running `sh t' I can get this to happen
on Fedora, but only intermittently.  I think it's the new option I
added, since I can get this to happen with `zsh -f -o notrapsasync', but
not with `zsh -f'.  So it looks like I've introduced a race.

This obviously needs fixing before we can release anything with the
option it it, but is going to take some tracing.  Here is what I've got.

I have two processes running:
pws      18664 14486  0 10:38 pts/2    00:00:00 sh t
pws      18665 18664  0 10:38 pts/2    00:00:00 sh t

(I thought I had another one but it seemed to be hung from a previous
go.)

18664 is waiting for output from the the $(...) to finish.  This is normal.

18665 is waiting for a job to finish in zwaitjob.  Somehow it's
got into a state where it wasn't prepared to handle the SIGCHLD, and
it's therefore missed it.

I'll keep looking.  Any suggestions would be gratefully received.

-- 
Peter Stephenson <pws@xxxxxxx>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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