bug#39962: 27.0.90; Crash in Emacs 27.0.90

[Pip Cet]

On Thu, Mar 19, 2020 at 7:17 PM Pieter van Oostrum
<pieter-l@vanoostrum.org> wrote:
> I had my keyboard macro translated to an Elisp function and then called this 
> a 100 times with dotimes. However, there was no crash, even though I had the 
> smaller stack size.
>
> In total I had the macro run some 300+ times without any crash. I just had it 
> run automatically (put it in a .el file, and used emacs -Q -l testfile.el), 
> so no keyboard/mouse interaction.

Did you use emacs -Q to produce the original crash, or just emacs? I
ask because it's possible something in your mode line specification
caused or exacerbated the problem.

> > If I'm right, it should be possible to trigger the bug by creating a
> > reasonably large session, running (garbage-collect) in an infinite
> > loop, and interacting with the mouse and keyboard while that is
> > happening. Or running your keyboard macro in a similar loop, of
> > course.
>
> But if I do it in a loop it will not react to the keyboard/mouse. Do you 
> think the asynchronous processing of these events will be sufficient, even 
> though no action is taken on these events?

I think so, but I'm not sure. I've been looking at this code for a
while, and I think the likeliest culprit is the mouse-over
highlighting code, possibly for the mode line. On GNU/Linux, the
behavior is quite odd: for the first second or so after starting a
loop, the mode line elements react to mouseover events, but not
afterwards. On the other hand, a millisecond delay ought to be enough
to catch it during the first second.