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From: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
Newsgroups: comp.sys.amiga
Subject: Re: How do I force a context switch? (more for the 1.3 wishlist)
Message-ID: <4559@jade.BERKELEY.EDU>
Date: Mon, 3-Aug-87 04:11:43 EDT
Article-I.D.: jade.4559
Posted: Mon Aug  3 04:11:43 1987
Date-Received: Tue, 4-Aug-87 01:35:55 EDT
References: <5175@utcsri.UUCP>
Sender: usenet@jade.BERKELEY.EDU
Reply-To: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
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Organization: Missionaria Phonibalonica
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In article <5175@utcsri.UUCP> flaps@utcsri.UUCP (Alan J Rosenthal) writes:
<In case you want to know, this is why I need to force a context
<switch.  I'm writing a program where several tasks are started.
<Through use of priorities, all are started at once.  One of these
<functions sets a global variable that others need.  If through bad luck
<another function starts running first and tries to use this global
<variable before it's set, it has to allow the first function to set it
<before proceeding.  Since this is the second line in the code of the
<first function, all it has to do is give up the rest of its cpu quantum
<this time around which will give the other task a chance to run before
<this one runs any more, thus setting the variable.

Like Mike Farren, my first reaction was "this isn't right." My second
reaction was "Why isn't he using semaphores?" Checking the RKM shows
why 0 there's isn't a good semaphore system in the Exec. All you get
is ports. At least it's better than what one did on v[67] Unix....

So could whoever at CBM is keeping track of things needed for 1.3 add
"real semaphores" to the list? Maybe as "semaphore.library"?

The best solution is probably to set the global variable in the
startup function, as suggested by Mike. From the sounds of things,
this variable will not be changed after it's started, so that should
work fine (otherwise, how does a function know that it's "not set"
yet?). If it does change, how do you handle exclusion during updates?
Will that method work for the startup period?

	<mike
--
ICUROK2C, ICUROK2.				Mike Meyer
ICUROK2C, ICWR2.				mwm@berkeley.edu
URAQT, I WANT U2.				ucbvax!mwm
OO2EZ, I WANT U2.				mwm@ucbjade.BITNET