Re: Strange hangs when visiting .el and .html files

[Adam Porter <adam@alphapapa.net>]

> Andreas Schwab <schwab@suse.de>:
>> On Feb 07 2024, Eric S. Raymond wrote:
>> 
>> > About a week ago I noticed that my Emacs was hanging when I attempted
>> > to visit my init.el file.  Then I saw the same hang when visiting an
>> > HTML file.  Other modes, such as text and C modes, are working normally.
>> 
>> Is it interruptable?  Then you can enable debug-on-quit to see where it
>> hangs.
> 
> I tried that first thing.
> 
> Ctl-G after the hang does interrupt it, but doesn't yield a trace.
> 
> It's a weird bug because it's so specific. Most Lisp modes are
> completely unaffected.

This sounds like a weird behavior that I've observed ever since Emacs 
28, but I've never been able to pin it down well enough to file a report 
about it.

Basically, what I observe is that:

1. Certain actions (like calling certain commands, perhaps including 
ones that activate a major mode) cause Emacs to spin with 100% CPU usage 
for some time, tens of seconds or even a couple of minutes sometimes.

2. It only happens when such an action happens for the first time in a 
session.

3. If I interrupt with C-g, everything appears normal; no errors, no 
partially initialized state, no weird behavior.  It's as if whatever I 
interrupted was "optional."

4. Over time (3 or 4 versions now), the actions that trigger this 
behavior have not been consistent.  I might even venture to say that, 
between different builds of the same version, the actions might not be 
consistent.

5. It seems to happen less now, on Emacs 29.1 (I still need to upgrade) 
than it did on builds of 28.0 and 28.1.

6. Without being able to verify it, I have the impression or intuition 
that it happens when Emacs loads a library for the first time in a 
session (I don't mean when it loads any library, just a certain one or 
ones, but I haven't been able to pin it down).

Over the past couple of years, I've heard a few other users mention 
observing similar behavior at times, but again, always being difficult 
to nail down.

If this seems like the same behavior you're seeing, maybe it's time we 
give this problem a name and an real bug report.