bug#25279: 26.0.50; Slowdown/crash on certain characters

[Richard Copley <rcopley@gmail.com>]

On 23 February 2017 at 16:19, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Tue, 21 Feb 2017 22:28:05 +0200
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: 25279@debbugs.gnu.org
>>
>> > From: Richard Copley <rcopley@gmail.com>
>> > Date: Tue, 21 Feb 2017 20:05:28 +0000
>> > Cc: 25279@debbugs.gnu.org
>> >
>> > Here's how to make Emacs hang without the need to uninstall any fonts,
>> > on Windows (not reproducible on GNU/Linux).
>> > 1. Type "M-x view-hello-file" (don't press return).
>> > 2. In quick succession, type "C-m" and then "C-g". *
>>
>> Thanks.
>>
>> > Eli, should I retitle this bug to "26.0.50; calling SendMessage inside
>> > critical section causes deadlock", or close this bug as a duplicate of
>> > the other "slow fonts on Windows" bugs and file a new report about
>> > the hanging?
>>
>> The former, I guess.  I will take a look when I have time.
>
> I think I found the reason: due to C-g, we were jumping to top-level
> while in a critical section, which is a very bad idea, because any
> non-main thread that tries to acquire the critical section after that
> will necessarily hang.
>
> Please try the latest master and see if any such hangs are still
> there.

Great, thank you. Sounds like your changes potentially eliminate
a fairly broad class of errors.
In terms of testing I can't say much about any other hangs (I would
if I could!), but that one recipe no longer hangs for me.

> Thanks for the recipe, it made it quite easy to catch the villain
> red-handed.

Nice to know.