Re: Getting articles asynchronously.....

[gsstark@MIT.EDU (Greg Stark)]

Actually, I was just in the process of writing a back end, and it occurred to
me I was taking an essentially asynchronous operation (interacting with a
subprocess) and serializing it.

This is an enormous lose, an existing interface allows users to start an
operation and go work on other things; it does this by putting most of the
work in the filter function.

The basic design to make Gnus do this would be to split each of the backend
interface functions into two steps.  Gnus would call a normal looking backend
function, but would pass a couple extra arguments.  One of the extra arguments
would be a function the backend function would call when it finshed its
processing.  I think it would also be useful to pass a nonce along as well and
pass it back to Gnus.

I would have said this would be very difficult to get right, but I also would
have said that about a lot of existing Gnus features.  And in my opinion this
is the key feature that would make Gnus a lot more useful.  I do a lot of
things in my Emacs and it frustrates me when it freezes for more than a few
seconds.

In fact, I think the least robust part of my backend is going to be the
joining of the synchronous backend interface and the asynchronous sub-process.
It would be easier to implement robustly if both were asynchronous.

greg




In case I wasn't clear here's an example of what I mean:

(defun nnchoke-retrieve-headers (articles call-back nonce &optional g s f)
  (start-process foo ...)
  (set-process-filter foo 'nnchoke-retrieve-headers-do-work)
  'in-progress)

(defun nnchoke-retrieve-headers-do-work (p s)
  ...
  process a lot of data
  but without blocking Emacs
  ...
  (funcall call-back nonce 'nov))


obviously some parts of the api need to be fixed to handle this, 
The nntp-server-buffer must either be passed down or dynamically bound.
The concept of a ``current group'' should probably be given up.
things like that, but nothing terribly major.
(except that i don't think the above example works because of the scoping of
call-back and nonce, hmm)

greg