Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!udel!rochester!PT.CS.CMU.EDU!VLSI.CS.CMU.EDU!blh
From: blh@VLSI.CS.CMU.EDU (Bruce Horn)
Newsgroups: comp.sys.mac
Subject: Re: What does access memory manager' mean?
Message-ID: <200@PT.CS.CMU.EDU>
Date: Mon, 19-Oct-87 10:03:21 EDT
Article-I.D.: PT.200
Posted: Mon Oct 19 10:03:21 1987
Date-Received: Tue, 20-Oct-87 02:50:57 EDT
References: <5365@jade.BERKELEY.EDU> <10620001@hpfclm.HP.COM> <6497@apple.UUCP>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 28
Summary: QD NOT Reentrant

(I'm not the right person to answer this, but here goes...)

Ed:

QuickDraw (and the Memory Manager, and the Resource Manager, and the Dialog
Manager, and the Font Manager...) is not reentrant.  In the same way that
the cursor calls are not reentrant, neither is QuickDraw (imagine setting
the port in one process, then running another that calls QD).  This is the
problem that is solved partially by Multifinder, which works hard to save
and restore all the appropriate globals.

It's not just a matter of saving and restoring globals, either;  shared
structures would need locks and synchronization.  Since Multifinder is
non-preemptive, it is much easier to handle the "multitasking", since there
is no need for locking the structures (context swaps never occur in the
middle of critical areas).

I don't know what they do with A/UX, which supposedly allows you to call the
Toolbox reentrantly.  I suspect that interrupts are turned off at critical
times (like when entering the ROM--so it really isn't reentrant).




-- 
Bruce Horn, Carnegie Mellon CSD
uucp: ...!seismo!cmucspt!cmu-cs-vlsi!blh
ARPA: blh@vlsi.cs.cmu.edu