Path: utzoo!attcan!uunet!super!rminnich
From: rminnich@super.ORG (Ronald G Minnich)
Newsgroups: comp.sys.amiga
Subject: Re: Need info on exceptions
Message-ID: <641@super.ORG>
Date: 23 Aug 88 17:43:31 GMT
References: <3794@louie.udel.EDU>
Sender: uucp@super.ORG
Reply-To: rminnich@metropolis.UUCP (Ronald G Minnich)
Organization: Supercomputing Research Center, Lanham, MD
Lines: 31

In article <3794@louie.udel.EDU> iphwk%MTSUNIX1.BITNET@cunyvm.cuny.edu (Bill Kinnersley) writes:
>I would think the "correct" way on the Amiga would be to send a
>message to the Task with the address of the array to be accessed,
>then wait for a reply.
   Sure, that is ONE way. Point is, on the Amiga, there are LOTS of ways.
>Even if Tasks are directly sharing memory, they need to be synchronized
>to avoid reading and writing data at the same time, so you do need
>at least a signal.
   well, for some cases, yes you need synchronization. But for the 
specific case of having information available about the state 
of a computation, you absolutely do not. The reason is that
the variables related to 'doneness' of the computation are 
just simply going to get larger with time*. So what if you read 
the variable just before it gets increased? Your monitor process 
might be a little off, but such would be the case if the clock 
interrupt came in before the variable got increased. 
   Back to the question at hand. The signalling that the person 
was looking for was to allow a process to be interrupted and thus
get state information ('doneness' of the computation) out of  that
process. This sort of thing has been done for years and years on 
Unix and when you think about what is happening it is really a 
poor man's way of spawning a lightweight process that prints out 
state informatino and quits. In addition the parent blocks. And you 
have all this yucky overhead. On the amiga, on the other hand
(or on the Sequent with its microtasking library, or maybe
SunOS4 with its task library) you can have a compute task and 
an information task. You don't interrupt the computation to get
information about the computation, and you can get information 
at any time, not just when a clock strikes.
ron
* Let's see, can we see they are monotonically increasing? Sure, why not?