Re: interrupting the Scheme process

[Ken Raeburn <raeburn@raeburn.org>]

Keisuke Nishida <kxn30@po.cwru.edu> writes:
> I have no idea of how this can be done right now.  Emacs checks for
> quit in some loops such as eval.  When the process is in the Scheme
> interpreter, we can't use the same way; instead, we have to generate
> a user interrupt.  I guess it is possible for Guile Emacs to bind C-g
> to generate an interrupt before calling the Scheme evaluator, but I'm
> not sure about this part.  Ken, do you have any idea?

Guile has some hooks for recording that an interrupt has occurred and,
at certain times, throwing an exception of some sort.  If we could set
that flag at C-g time, if Scheme code is currently running, might that
do the trick?  Then Scheme can trap the exception if it wants, but
otherwise we throw back to the containing Lisp call.  Propagating the
unwind through possibly multiple lisp<->scheme interfaces could be
hairy though; I haven't looked very closely at that stuff.

> Also, once we come to support multi-thread programming with Emacs,
> things become more complicated.  Probably we have to maintain threads
> in the same way as shells; that is, Emacs will have a "current thread"
> and "background threads", and the user may quit only the current thread
> by typing C-g, whereas background threads must be killed by a special
> command like M-x kill-thread.

Hm...that might be a way to do it.  I also wonder if we might have
cases where we want to send the interrupt to multiple threads -- i.e.,
if the "foreground" thread is sitting around waiting for N tasks to
finish (e.g., get new news from news.mycompany.com, get email from
pop.mycompany.com, get new news from news.redhat.com, etc), might we
want to interrupt all of them and unwind the main thread only after
they've died off?

I suppose we could have a "spawn and wait for multiple threads"
function which implements all of this on top of the scheme^Wplan you
describe, by trapping the interrupt...

Ken