Path: utzoo!utgpu!watmath!att!rutgers!ucsd!helios.ee.lbl.gov!ux1.lbl.gov!beard
From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need info on multitasking capabilities on the mac
Message-ID: <4294@helios.ee.lbl.gov>
Date: 27 Nov 89 00:36:31 GMT
References: <6391@tank.uchicago.edu> <9072@hoptoad.uucp>
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 37

In article <9072@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>I wonder how they do that.  Can anyone provide any information?  My
>first thought was to schedule your file transfer protocol off the
>vertical retrace manager, but your tasks don't get called when you're
>switched out.

Ah, but one of the Multi-Finder technotes states that vbl tasks that are
in the System Heap will continue running even in other contexts.  Here's
how I do it:

struct jump_vector {
	short jmp;		/* place to stuff a 0x4e21 jump instruction. */
	ProcPtr addr;	/* the place to jump to. */
};
typedef struct jump_vector jump_vector;

...

main()
{
	jump_vector *the_jump;

	the_jump = (jump_vector*)NewPtrSys(sizeof(jump_vector));
	...
	the_jump->jmp = 0x4e21;
	the_jump->addr = (ProcPtr)vbl_routine;	/* routine we want called. */

	/* then, call VInstall with the vblAddr field of your VBLTask record
		set to point to the_jump... */
	...
}


-------------------------------------------------------------------------------
-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
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