Re: Asynchroneous image retrieval in HTML rendering

[Lars Magne Ingebrigtsen <larsi@gnus.org>]

Antoine Levitt <antoine.levitt@gmail.com> writes:

>> I think the fix here might be to introduce a new variable
>> `url-asynchronous-dns-lookup' (or something), and then have shr bind it
>> to make url.el more asynchronous.  The pauses we experience today when
>> trying to do asynchronous URL retrieval aren't acceptable.  Especially
>> if a domain is down or semi-down -- reading the articles becomes almost
>> impossible.

Oopsie.  Actually, the image retrieval in Emacs 24 was extremely
synchronous.  Due to changes in `open-network-stream', the :nowait flag
was no longer passed on, so all connections were established
synchronously, even if url.el tried to do it asynchronously.

I've now fixed this and pushed the fix to Emacs 24.

> Why is DNS even synchroneous in the first place? I'd expect
> "asynchroneous" to mean that both DNS lookup and data transfer are
> non-blocking.

Emacs uses the built-in resolver (from C), and it does it in the main
Emacs thread.  So whenever you resolve something in Emacs, *everything*
in Emacs stops.

I've written the dns.el resolver in Emacs Lisp, but, of course, it's not
as sturdy as the libc one.  (And only works on Linux.)  A better fix
would be to write a C-level resolver that forks its own thread, does the
resolving, and then does a callback.

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/