bug#3399: Crash in multi-TTY mode

[YAMAMOTO Mitsuharu]

>>>>> On Thu, 28 May 2009 09:14:06 -0400, Stefan Monnier 
>>>>> <monnier@iro.umontreal.ca> said:

>> 1. Older libX11 that doesn't care about XlibDisplayDfltRMDB at all.
>> 2. Newer libX11, when the first XGetDefault call sets dpy->db to a
>> non-NULL value.
>> 3. Newer libX11, when the first XGetDefault call sets dpy->db to NULL.

>> Case 3 corresponds to the problematic scenario I mentioned in my
>> previous mail and the other cases should work fine currently.  Undoing
>> my recent change means that we don't destroy the database ourselves,
>> and it leaks memory in Case 2 and 3.

As I corrected, the memory leak happens only in Case 2, which is the
most common case I guess.

> What if (as asked) we don't just undo your change, but additionally
> return to freeing the DB (so we'll get a crash in case 1)?  Will we then
> also get a crash in case 2 or 3?

It will crash in Case 3 as well as 1.  XCloseDisplay destroys the
associated database because XlibDisplayDfltRMDB is set, although the
database was not actually what's allocated by some XGetDefault call.
That's why I consider this is a bug in libX11.

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp