Re: 64-bit emacs crashes a lot

[Ryan Johnson <ryan.johnson@cs.utoronto.ca>]

On 16/08/2013 4:56 AM, Eli Zaretskii wrote:
> I'm not subscribed to this list, so if you want me to reply, please CC
> me explicitly.  Besides, this discussion should be moved to
> emacs-devel@gnu.org, since I don't see anything Cygwin specific here
> at this point.
>
>> Date: Thu, 15 Aug 2013 16:55:18 -0400
>> From: Ryan Johnson <ryan.johnson@cs.utoronto.ca>
>>
>> On 15/08/2013 1:10 PM, Eli Zaretskii wrote:
>>>> Date: Thu, 15 Aug 2013 12:58:02 -0400
>>>> From: Ken Brown <kbrown@cornell.edu>
>>>> CC: Eli Zaretskii <eliz@gnu.org>
>>>>
>>>> Eli is the expert on bidi.c (he wrote it).  He can probably tell you
>>>> whether you've really bumped into an emacs bug here.
>>> There's nothing wrong with bidi.c here, it just aborts because it is
>>> handed an invalid character codepoint.  It would have been useful to
>>> see the value of that character.
>> I guess I would just consider crashing to be overkill for a bad byte on
>> the input stream...
> It's not a crash, it's a deliberate abort.  Any invalid codepoint at
> such low level of the Emacs display engine means only one thing: a
> bug, and a grave one at that.  Such bugs must be flagged prominently
> and unequivocally, prompting users to report them.  We could in
> principle "recover" by substituting some other character, but such
> recovery would only sweep a grave problem under the carpet.  Since
> Emacs isn't a safety-critical program, and auto-saves your edits
> before it commits suicide, such recovery feature is deemed
> inappropriate, and detrimental to the general quality of Emacs code in
> the long run.
OK, makes sense.

>> and in any case, if 5-byte UTF-8 is illegal, and
>> worth dying for, wouldn't it make sense to die right away rather than
>> processing it so something else can croak down the road?
> See above: yes, it's worth dying for, because I'm quite sure this is a
> sign of a very serious trouble in the session anyway.  Why does it
> matter for you, as a user, whether we abort here or "down the road"?
> The principle is to die as soon as possible, because in many cases
> this allows to identify the culprit faster and easier.  IOW, dying
> sooner and faster helps the Emacs maintainers to find and fix problems
> without any real effect on the users.
Re die as soon as possible: We're in violent agreement: I argued 
that---if 5-byte UTF-8 is illegal---emacs should abort at the decoding 
stage (= earlier) rather than at some later point when it discovers the 
too-large value. In any case, though, I can't repro on a debug build so 
this whole thing may be moot.

Ryan