Re: asynchronous backends

[Stainless Steel Rat <ratinox@peorth.gweep.net>]

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>>>>> "KR" == Ken Raeburn <raeburn@cygnus.com> writes:

KR> This "just" means the multitasking has to be done at the application
KR> (gnus elisp) level.

Problem: there is no multitasking involved inside the Emacs kernel.  There
is a single process thread and a queue of functions to be evaled.
Everything that happens in Emacs is pushed into this queue and is evaled in
sequential order.  This includes the process filters associated with
asynchronous processes.  What makes process filters appear to be
multitasking is that they are automatically pushed into the queue by their
associated I/O streams.  When they are invoked while Emacs is "idle" their
evaluation is practically transparent.

That is, unless so much data is coming in through the I/O streams that the
process filters are being pushed into the queue every cycle.  If you want
an example of this, turn on asynchronous prefetch in Gnus, set the prefetch
number to something huge like 100, open a large newsgroup (at least as many
articles as you have your prefetch set), and select the first article.  Now
'n' to select the next and time how long it takes for that to happen
(assuming Gnus does not barf on the data overload :).

If you really want to multitask Gnus or Emacs in general you need to invoke
a new instance of Emacs and let the operating system handle it.

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