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

[Eli Zaretskii]

> 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.

> Emacs master has a pronounced tendency to hang in various other
> circumstances too.

Showing backtraces from the relevant threads when it hangs would be
appreciated.