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

[Eric S. Raymond]

Adam Porter <adam@alphapapa.net>:
> 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.

OK, I tested your theory by visiting my HTML home page, interrupting the 
resulting
hang, and then visiting the page again.

It didn't hang, and now seems to be operating normally.

So I think we are in fact looking at the same bug.  Nice to know I
wasn't hallucinating, and I'm guessing you're feeling the same relief
on reading this.

Proposed title:  "Repeatable hang on first load of certain major modes".
I'd file the bug now, but it sounds like you've experienced it over more
versions and contexts than I have, so you can add more detail than I could.
The only thing I can add to your report is that the problem goes back past
version 28, at least as far as 27.1.

You can add to the report that I have seen this hang consistently in
27.1 and a recent repo head version, 30.0.50.  And the modes I've seen
hang are elisp mode and whatever is invoked for HTML files.

If you reply with an issue URL I'll look it over and probably
comment.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>