bug#24109: 24.5; Long lines in message mode make Emacs irresponsive

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuri D'Elia <wavexx@thregr.org>
> Cc: 24109@debbugs.gnu.org, djcb@djcbsoftware.nl, Christophe.Troestler@umons.ac.be, rudalics@gmx.at
> Date: Tue, 30 Aug 2016 17:51:48 +0200
> 
> >> Emacs is stuck in try_window calling display_line, where the "it" parameter remains constant.
> >
> > What do you mean by "it parameter remains constant"?  That is a large
> > structure; what parts of it remain constant?
> 
> The address of the structure remains constant (that is, display_line is
> called with the same pointer). I don't know if this is expected to
> change or not.

This is expected.  This structure is the object used for iterating
through buffer text in order to prepare its display in a window.  A
single object is used by try_window each time it is called.

What should NOT happen is that the values of it.current.pos stay
constant, or cycle endlessly between the same values.  If you can look
at that, please do.

> Is there some way to conveniently dump the entire buffer state to a file
> so we can debug this by reloading the content without having the mail
> client in the way?

Not that I know of.

I can provide guidance for debugging this, if you can afford it.

Thanks.