Path: utzoo!attcan!uunet!husc6!mailrus!ncar!gatech!udel!mmdf
From: iphwk%MTSUNIX1.BITNET@cunyvm.cuny.edu (Bill Kinnersley)
Newsgroups: comp.sys.amiga
Subject: Re: Need info on exceptions
Message-ID: <3867@louie.udel.EDU>
Date: 29 Aug 88 08:03:15 GMT
Sender: usenet@udel.EDU
Lines: 36

[In "Re: Need info on exceptions", Ronald G Minnich said:]
:
: In article <414@brambo.UUCP> morgan@brambo.UUCP (Morgan W. Jones) writes:
: >Somebody forgot their Operating Systems course, eh?
: >The problem with all of these approaches, of course, is that you've
: >got two processes reading the same data at the same time, or, more
: >specifically, one reading the data while the other is still writing.
: Seems like you might need to actually use this sort of system
: for a while before you understand it. I can't see why this is
: so hard for people to get.
: No, this is NOT A PROBLEM. You have a single writer, single reader.
: The variable relating to DONENESS will INCREASE SLOWLY AS THE
: COMPUTATION PROCEEDS. YOU CAN LOOK AT IT AT ANY TIME!
: PEOPLE DO THIS SORT OF THING ALL THE TIME!!! AMAZING, HUH?
: The writer is the compute process. the reader is the 'front panel'.
: Think a little bit before you comment. Or get a little experience
: with this sort of thing before you comment. Or don't comment.
: Seems that your level of knowledge does not extend much PAST
: an operating systems course!
: Or, try again,
:         NO, YOU DON'T NEED SEMAPHORES FOR THIS PROBLEM!!!!
: Get it?
: ron
:
Seems to me it depends on what you're computing, Ron.  You're right if
it's just one variable.

Suppose one task is updating a chess board and the other task is printing
it out.  The printer may start up just as a piece has been moved to
a new square, but not yet erased from the previous one.

In general, the data set may pass through inconsistent states, and a
semaphore is a way of preventing this problem.


--Bill K.