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From: new@ee.udel.edu (Darren New)
Newsgroups: comp.sys.amiga.misc
Subject: Re: True Multitasking
Message-ID: <42598@nigel.ee.udel.edu>
Date: 23 Jan 91 18:43:10 GMT
References: <MWM.91Jan18153532@raven.relay.pa.dec.com> <42149@nigel.ee.udel.edu> <672@tnc.UUCP>
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In article <672@tnc.UUCP> m0154@tnc.UUCP (GUY GARNETT) writes:
>As I understand it, the Amiga does not have "threads" or "lightweight
>processes".  The Amiga does make a distinction between "processes" and
>"tasks".  A process could be described as a task that is known to
>AmigaDOS (Amiga EXEC handles multitasking, at a level below AmigaDOS).

Not really.  AmigaDOS does indeed have lightweight processes, which
are called "tasks".  An AmigaDOS "process" is a task with an easily-
locatable communication buffer for use by certain system libraries
(primarily the file system).  However, tasks can and do perform I/O
via message passing. The filesystems simply require that the I/O
be done to a certain location.

>Processes have a current directory, standard input and output streams,
>and some other things which tasks do not.  

Yes. AmigaDOS "processes" are supersets of tasks, but the differences
have nothing to do with addressing or scheduling.

>Although all of the tasks and processes on the Amiga share an address
>space, it is not intended that there be multiple execution traces
>through the same code and data (with the well-defined exception of
>certian operating system code).  

There can be. What do you mean by "the same code"?  The same executable
image in memory? Happens all the time (with "resident" programs), i.e.,
shared-code in UNIX-speak.  Many programs (esp games and telecom programs)
have multiple tasks using the same non-shared executable.

>You *CAN* do it, but you do not get
>the same benefits that threads get - the operating system overhead is
>the same, and writing code to work this way adds its own overhead.

It is exactly the same as threads.  Tell me what a thread gives you
that an AmigaDOS task does not?  Or vica versa.    -- Darren

-- 
--- Darren New --- Grad Student --- CIS --- Univ. of Delaware ---
----- Network Protocols, Graphics, Programming Languages, 
      Formal Description Techniques (esp. Estelle), Coffee, Amigas -----
              =+=+=+ Let GROPE be an N-tuple where ... +=+=+=