zsh 4.3.9: Interrupted "tcsetattr" call problem, tiling-wm related

zsh 4.3.9: Interrupted "tcsetattr" call problem, tiling-wm related

[Lionel Flandrin]

Hi everybody, I haven't subscribed to this list so please include me
in Cc in your replies.

I think I have spotted a bug related to this one:
http://www.zsh.org/mla/workers/2007/msg01121.html

Basically, *sometimes* I get an unusable prompt when I start a new
terminal, if I type <TAB> I get a litteral tab, if I type "key up" I
get ^[[A etc...

A strace told me the problem is that the terminal bufferizes the
output line by line, i.e. is in ICANON termios mode.

A couple of grep and dirty fprintf in the source code later, I think
I've found the root of the problem at Src/utils.c line 1440:

1440          tcsetattr(SHTTY, TCSADRAIN, &ti->tio);
1441      /* if (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1) */

(It's interresting that the bugfix is almost already there :).

Indeed, the problem seems to be that I use a tiling WM (stumpwm) that
resizes the term as soon as it's created, sending (I'm just guessing
there) the SIGWINCH signal to zsh interrupting the tcsetattr.

If I add some debug code:

  while (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1)
  {
     FILE *f = fopen("/tmp/fail.out", "a");
     fprintf(f, "tcsetattr failed: %s\n", strerror(errno));
     fclose(f);
  }

I do get: "tcsetattr failed: Interrupted system call"

If I change the call to:

  while (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1 && errno == EINTR);

It fixes the problem.

I hope this helps.

(Thank to ft on freenode's #zsh for his help).

-- 
Lionel Flandrin

Re: zsh 4.3.9: Interrupted "tcsetattr" call problem, tiling-wm related

[Peter Stephenson]

On Fri, 27 Feb 2009 17:20:25 +0100
Lionel Flandrin <lionel@svkt.org> wrote:
> A couple of grep and dirty fprintf in the source code later, I think
> I've found the root of the problem at Src/utils.c line 1440:
> 
> 1440          tcsetattr(SHTTY, TCSADRAIN, &ti->tio);
> 1441      /* if (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1) */
> 
> (It's interresting that the bugfix is almost already there :).

... just after the line that says "Princeton's include files are screwed
up".  It's interesting we're relying on an ad-hoc fix for a problem
(although not related to this one) on a single system that probably
disappeared ten years ago.

> Indeed, the problem seems to be that I use a tiling WM (stumpwm) that
> If I change the call to:
> 
>   while (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1 && errno == EINTR);
> 
> It fixes the problem.

That looks fine, I've committed it.  Thanks.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070

Re: zsh 4.3.9: Interrupted "tcsetattr" call problem, tiling-wm related

[Bart Schaefer]

On Mar 2, 10:23am, Peter Stephenson wrote:
}
} On Fri, 27 Feb 2009 17:20:25 +0100
} Lionel Flandrin <lionel@svkt.org> wrote:
} >   while (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1 && errno == EINTR);
} 
} That looks fine, I've committed it.  Thanks.

I wonder if queue_signals/unqueue_signals around the tcsetattr might be
more appropriate?

Re: zsh 4.3.9: Interrupted "tcsetattr" call problem, tiling-wm related

[Peter Stephenson]

Bart Schaefer wrote:
> On Mar 2, 10:23am, Peter Stephenson wrote:
> }
> } On Fri, 27 Feb 2009 17:20:25 +0100
> } Lionel Flandrin <lionel@svkt.org> wrote:
> } >   while (tcsetattr(SHTTY, TCSADRAIN, &ti->tio) == -1 && errno == EINTR);
> } 
> } That looks fine, I've committed it.  Thanks.
> 
> I wonder if queue_signals/unqueue_signals around the tcsetattr might be
> more appropriate?

That doesn't actually block the signal, it just marks that we should
queue any shell code activities.  We would still receive the signal, and
hence the system call would still fail with EINTR.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070