bug#26710: Fwd: 25.2; project-find-regexp makes emacs use 100% cpu

[Eli Zaretskii <eliz@gnu.org>]

> Cc: hariharanrangasamy@gmail.com, 26710@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Tue, 2 May 2017 13:00:06 +0300
> 
> On 02.05.2017 10:15, Eli Zaretskii wrote:
> 
> > Can you explain the significance of xref--regexp-syntax-dependent-p's
> > tests?  I don't know enough about xref to grasp that just by looking
> > at the changes.
> 
> When it returns nil (the regexp is not affected by syntax-table):
> 
> If the file containing the hit is not open, we now skip inserting the 
> first few lines of that file into the temporary buffer, and calling 
> set-auto-mode.
> 
> And, whether it's open or not, we skip the syntax-propertize call.

OK, I will look at that function with this in mind.

> Still, if the filter function and sentinel functions take a lot of time 
> (and/or get called a lot), like it will be in this example, the UI can't 
> as responsive as usual, can it?

The sentinel/filter won't be called at all if keyboard/mouse input is
available.  Once they are called, if each call takes a long processing
time, the UI could feel sluggish, yes.  But I don't quite see how
using threads will avoid the same problem, since the mechanism for
thread switch is basically the same as for multiplexing UI with
subprocess output.

> I'd like a more general advice first. E.g. do we want to go this road? 

IMO, we should first explore the async subprocess road.

> It seems a bit brittle, though: if the process filter is supposed to be 
> calling the callback for each item, the callback has to be in place 
> right away. And the process will be started before that happens.

You can countermand that by using make-process with the :stop
attribute, then use 'continue-process' when everything is set up.

> We'll probably be saved by filters having to wait until the current 
> command finishes executing, though.

Not sure I follow you: a filter function is called whenever some
output arrives from the subprocess.  So they don't need to wait for
the subprocess to finish.