Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!samsung!uunet!mcsun!ukc!edcastle!helium!gordonc
From: gordonc@aifh.ed.ac.uk (Gordon Cameron (RA DAI))
Newsgroups: comp.windows.x
Subject: Re: Xview: Interrupting a Notify Procedure
Message-ID: <1991Apr24.211819.26355@aifh.ed.ac.uk>
Date: 24 Apr 91 21:18:19 GMT
References: <3098@sparko.gwu.edu>
Organization: Dept AI, Edinburgh University, Scotland
Lines: 93

From article <3098@sparko.gwu.edu>, by darken@seas.gwu.edu:
> Here's the problem:
> Say I have a panel with 2 buttons on it. When I hit
> button #1, I want to start a process which will continue
> until button #2 is hit. How can I interrupt the notify
> procedure of button #1 when #2 is hit? As I see it,
> the pressing of #2 will not be recognized until #1
> is completed processing. I looked into events in
> addition to notifications but nothing works yet and
> the manual is rather shady in this area. Thanks in
> advance!
> 

You could try something like this :

/* Globals */
int program_state , finished ;

main() {
	---
	---

	program_state=DOING_LOOP ;
	while (running==TRUE) {
		xv_main_loop(----)
		if (program_state=DOING_SOMETHING) {	/* (1) */
			do_something() ;
			clean_up() ;			/* (2) */
			program_state=DOING_LOOP ;
		}
	}
}

<Callback routine for button #1> {
	program_state=DOING_SOMETHING ;
	notify_stop() ;
}


<Callback routine for button #2> {
	finished=TRUE ;	
}


do_something() {
	finished=FALSE ;
	/* Insert your code here and in it periodically do this...

		notify_dispatch() ;
		if (finished==TRUE) {
			printf ("Finished off !!!\n") ;
			return ; // This takes you back to (2) in main 
		}


	*/
}

What this does is to run the routine 'do_something' when you press
the button #1. How ?? Pressing the button triggers the callback
which sets a global variable, and calls notify_stop.
The notifier returns to the top level, and then notify_start
and xv_main_loop return.

This leaves you in position (1) in the code.  Since you have set
the variable program_state, the routine 'do something' executes.

Periodically in this routine, you should make calls to 
notify_dispatch(), which will make a single pass through the
notify cycle. If you have pressed button #2, then all you will
have done is to set the variable finished to TRUE. This is
detected, and 'do_something' returns so you end up at point (2).
You can now do whatever you want before continuing with the
application (perhaps doing some graphical output).

xv_main_loop then gets called again, and so you are back to where
you started. I've set a variable running, which when you unset
and do xv_destroy(Frame) will have the effect of quitting the
application.
(To be complete you should write a notify_interspose_destroy_func
which sets the variable running to FALSE, so the window quit works)


Hope this is useful - If you're interested, get the O'Reilly book
'XView Programming Manual' by Dan Heller, as its excellent.
(see pp 397-400)

Gordon Cameron,
Department of Artificial Intelligence,
University of Edinburgh,
Scotland

e-mail : gordonc@uk.ac.edai.fh