Re: interrupting the Scheme process

[Keisuke Nishida <kxn30 at po dot cwru dot edu>]

Ken Raeburn <raeburn@raeburn.org> writes:

> 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.

It seems Emacs catches the interrupt by interrupt_signal in keyboard.c,
so we could modify this function so that it also sets the Guile's flag.
If this works, we can convert the signal from Guile into a Emacs's quit
signal.  In case this doesn't work, I don't know what to do.

/* This routine is called at interrupt level in response to C-G.
 If interrupt_input, this is the handler for SIGINT.
 Otherwise, it is called from kbd_buffer_store_event,
 in handling SIGIO or SIGTINT.

 If `waiting_for_input' is non zero, then unless `echoing' is nonzero,
 immediately throw back to read_char.

 Otherwise it sets the Lisp variable  quit-flag  not-nil.
 This causes  eval  to throw, when it gets a chance.
 If  quit-flag  is already non-nil, it stops the job right away.  */

SIGTYPE
interrupt_signal (signalnum)	/* If we don't have an argument, */
     int signalnum;		/* some compilers complain in signal calls. */

> 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?

Probably.  We should kill the parent thread and its children at the same
time, though I guess we would still need kill-thread to kill detached
threads, which are "background" threads.  We don't want to close a GTK
window, which may run in a separate thread, just by typing C-g, for example.

> 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...

Anyway, we can't work on this until your Guile-based Emacs appears :)

-- Kei