Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!ginosko!uunet!mcsun!hp4nl!philapd!ssp1!roelof
From: roelof@idca.tds.PHILIPS.nl (R. Vuurboom)
Newsgroups: comp.object
Subject: Re: "Messaging" (Re: Reentrant code)
Message-ID: <271@ssp1.idca.tds.philips.nl>
Date: 10 Oct 89 16:48:41 GMT
References: <4540@internal.Apple.COM> <8636@goofy.megatest.UUCP> <5678@portia.Stanford.EDU>
Organization: Philips Telecommunication and Data Systems, The Netherlands
Lines: 35

In article <5678@portia.Stanford.EDU> dchapman@Portia.Stanford.EDU (David Chapman) writes:
>
>Interprocess function calls imply blocking (you get a return value from
>the callee).  Message passing implies no blocking (except perhaps for
>queue overflow).  The return value is from the message passing system
>itself and tells you if the message was accepted (i.e. transmitted
>properly and acknowledged).  This is a fundamental difference, and is an
>OS problem instead of an OOP problem (since most OOPs are not parallel
>programming languages).

>
>If your function calls don't block they are messages, by the way.

Message passing is, in essentia, the passing of information (data) from
one entity to another entity. The message passing paradigm can be blocking
(wait for my call) or non-blocking (I'll drop you a letter). Interprocess
communication is generally message passing since processes are by definition
generally separate entities.

A function call (irrespective of its blocking status) may or may not be a
message, it depends on whether the concept of entities which can pass
information is present in the program and whether the function actually
passes information (in a blocking or non-blocking fashion).

This does not demand the presence of more than one entity: an entity can
send a message to itself but the concept of an entity must exist within
the world view of the program.


-
-- 
"Geld groeit me niet op de rug." Literally: "Money doesn't grow on my back."
(Often overheard at the supermarket counter from mothers to their kids.)
Roelof Vuurboom  SSP/V3   Philips TDS Apeldoorn, The Netherlands   +31 55 432226
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