Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uwvax!astroatc!nicmad!madnix!jason
From: jason@madnix.UUCP (Jason Blochowiak)
Newsgroups: comp.sys.apple
Subject: Sublaunching (was Re: Finder Data File Format)
Summary: I dunno if that'd work
Keywords: launching, programming, //gs
Message-ID: <1113@madnix.UUCP>
Date: 15 Feb 90 14:25:49 GMT
References: <9001260129.AA04439@apple.com> <38342@apple.Apple.COM> <1214@darkstar.ucsc.edu>
Reply-To: jason@madnix.UUCP (Jason Blochowiak)
Organization: ARP Software, Madison, WI
Lines: 38


	Although it'd be nice to be able to launch something without the
application knowing about it, I think it'd be kind of dangerous. Reason:
There's no simple way (that I'm aware of, anyways, and I _have_ looked into
this) to wrap/unwrap an application's context. Things like normal tools should
be easy enough (save their WAP), but there are a few wierd tools. The resource
mgr is one, but they provided support for context switching. The misc toolset
is another - how is it possible to safely wrap all of the heartbeat tasks,
for example? It wouldn't even be safe to search through the heartbeat queue
and (temporarily) remove all of the entries that are located in an area
owned by the application's ID. It's entirely possible that, for example, the
thing has loaded a bunch of shell utilities, and _they_ installed some
heartbeat tasks. Then, of course, there's GS/OS - the application may have
open files, possibly some pending i/o, etc.

	The point of all of this is that 1) You'd have to do a complete
context wrap of the current application to safely launch another one, and
2) Getting the context wrap would be one hell of a trick (and if you did it,
writing a Switcher would more likely be a better application of the
technology).

	As usual, I may have missed something really important to all of
this... I personally would like one of the "unused" standard toolcalls to
be used as a wrap/unwrap. For example:
context[windMgr] = WindContext(getContext,nil,id); and then,
WindContext(setContext,context[windMgr],0);

	Where xxxContext would return a new handle containing its context
when requested, or set the context based on the contents of a handle. As
mentioned above, for most tools, this would just be a matter of sticking
the WAP (which stands for Work Area Pointer, btw) into a new handle. All
sorts of neat things could then be written, and the writer wouldn't have to
worry about future compatibility, as the tools themselves would handle the
context wrap/unwrap...
-- 
                      Jason Blochowiak - jason@madnix.UUCP
or, try:         astroatc!nicmad!madnix!jason@spool.cs.wisc.edu
       "Education, like neurosis, begins at home." - Milton R. Saperstein