Re: 23.0.50; ps-print-buffer-with-faces hangs on w32

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 10 Jan 2008 17:11:36 +0100
> From: "Lennart Borgman (gmail)" <lennart.borgman@gmail.com>
> CC: Vinicius Jose Latorre <viniciusjl@ig.com.br>, 
>  emacs-pretest-bug@gnu.org, Eli Zaretskii <eliz@gnu.org>
> 
> What I was reporting was that under certain (rather common conditions) 
> Emacs can hang if a user tries to print a file. Emacs hangs very badly 
> and can not be interrupted. You have to kill Emacs from outside - and 
> that of course means that the user can loose data.
> 
> (It has nothing per se with ps-print-* to do, it hangs in the same way 
> if one uses print-buffer. I actually did M-x ps-print-buffer just to see 
> how Emacs failed.)
> 
> So my question is what we can do about this?
> 
> I doubt that there is anything we easily can do technically about it 
> since I notice that in a cmd.exe console
> 
>     copy /b some-non-emtpy-file.txt PRN:
> 
> hangs the console window rather badly.

Exactly.  That will happen to any program that tries to write to a
device that does not exist.  If someone knows how to detect such
devices without hanging, I'd be glad to incorporate such detection
into Emacs.

> What we can do is to warn the user. The best way IMO 
> would be to add a y/n question in the function 
> direct-print-region-helper in dos-w32.el that warns the user that Emacs 
> might hang.

I'd be terribly annoyed to have such question each time I print.

> (And of course an option to bypass the question.)

If the option is off by default, it won't help.  If it is on, it will
annoy, and will generally be useless anyway, since the user cannot do
anything about this warning, except give up the printing command.  If
she doesn't give up, and she is in your situation, she will hang.
There's no way for her to find out whether she will or will not hang.