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Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!cuae2!killer!elg
From: elg@killer.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: "kill"
Message-ID: <1422@killer.UUCP>
Date: Fri, 28-Aug-87 00:32:19 EDT
Article-I.D.: killer.1422
Posted: Fri Aug 28 00:32:19 1987
Date-Received: Sat, 29-Aug-87 16:52:35 EDT
References: <1708@amiga.amiga.UUCP>
Organization: Bayou Telecommunications
Lines: 52

in article <1708@amiga.amiga.UUCP>, bart@amiga.UUCP (Barry A. Whitebook) says:
> this is amiga!bart: just a little background on why there is no "kill"
> (and why memory gets fragmented...)

[bunches of reasons]

> this posting is not to discourage the thought of a "better" solution:
> but as long as we have no MMU...
> 
> bart.

I'm in the midst of a multitasking kernal right now, somewhat similiar in
concept to the Amiga's except a bit simpler, and I, too, at first saw no easy
way to keep track of all resources. First, there's message ports. Well, these
are part of the kernel, so the kernel can send a "process killed" message
through open ports, and the i/o manager et. al. could handle gracefully
closing files and so forth. So that handles tracking i/o. Then, there's memory
management.  It is possible to tag each block of memory here with a process
number, just like above, and tell the malloc that process xyz died and add its
memory to the freelist. However, this would also require linking together all
the used blocks of memory into a "usedlist". So we're talking about 3 bytes of
overhead for each block of memory. So how large is the average block of memory
in an Amiga? I dunno. Then there's the bytes used for messages. You'd have to
say that they were part of the memory of the sending process, because
generally "C" malloc library routines request a large amount of memory and
subdivide it.  So the first task upon killing the process will have to be
emptying out any pipes that have messages pending from this process, because
they are null and void... 

Since my project is for a dedicated environment, on a machine that I won't
disclose for fear of being laughed out of this newsgroup, I'll never have to
face any of those questions. But, whereas I started out skeptical that
resource tracking was possible, I am now much more optimistic... 

  I/O: DOS keeps track of what process associated with what file, for orderly
shutdown. "kill" routine sends some sort of KILL packet with associated
procid, telling it who to zap.  
  Message ports: Message port handler keeps track of these. Things can get
hairy here with "KILL" packets and "deadly embrace" and such, but all in all,
things can be made managable.  
  Memory: Tag blocks with process IDs. Have "usedlist" as well as freelist so
that killr can find the tagged blocks when killing RAM. problems: overhead.
Depends on how big of blocks applications request.

So there's the three major resources of the Amiga, tracked on a per-process
basis. So it SHOULD be possible, WITHOUT a MMU. It just all depends on how
braindamaged the DOS REALLY is, as to whether it's possible ON THE AMIGA....
--
Eric Green   elg@usl.CSNET     Do-it-yourselfer's maxim:
{cbosgd,ihnp4}!killer!elg      Don't force it, use a bigger hammer!
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