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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: best way to detect command-. interrupt?
Message-ID: <33405@ucbvax.BERKELEY.EDU>
Date: 30 Dec 89 04:04:29 GMT
References: <694@nems.dt.navy.mil> <33392@ucbvax.BERKELEY.EDU> <9421@hoptoad.uucp> <4539@helios.ee.lbl.gov> <9428@hoptoad.uucp>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 32

It is beginning to sound like what we need is an INIT that launches a
command-period driver. The command-period driver would patch the PostEvent
trap before multi-finder is installed.  Applications interested in
command-periods would register a callback address with the driver using a
control call, inform the driver of suspend and resume events, 
using a second control call, and de-register the callback before they
quit.

If a command period occurs, then the keyboard handler will call PostEvent,
the command-period driver will detect it. If the last suspend/resume
message was a "resume" the driver will assume that one of the registered
applications was frontmost, remove the command-period from the queue, and
call the callback address. Otherwise, it will assume an unknown
application is frontmost and do nothing.

Since the callback address is being called at interrupt time, there is
a problem accessing the application's globals. We'll have the
command-period driver cache the application's currentA5 when the
application  registers the callback, and the driver will setup A5 before
calling the callback, and restore it afterward.

Since the callback address is being called at interrupt time, the callback
is limited in what it can do: it can't move memory or make most system
calls. It could set a flag, or do a C longjump.  If you do a longJump,
your ongJump catcher should set a flag that your event loop should check,
so that when your event loop next runs, it can execute a cleanup routine
to cleanup any structures that were not properly deallocated by the
longjump.

--- David Phillip Oster            --  No, I come from Boston. I just work
Arpa: oster@dewey.soe.berkeley.edu --  in cyberspace.
Uucp: {uwvax,decvax}!ucbvax!oster%dewey.soe.berkeley.edu