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From: snykanen@cs.Helsinki.FI (Silja Nykanen)
Newsgroups: comp.parallel
Subject: Re: A Linda Question (sending an answer from Jerry Leichter)
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Date: 7 Jan 91 13:47:39 GMT
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Thanks to Jerry Leichter (leichter@LRW.COM) for sending me an interesting 
reply to a Linda Question.
At the end of the message he writes

	"Feel free to post a copy of this message to comp.parallel - 
	 I have no easy way of posting to Usenet newsgroups from here."

.. so here is the copy of the message:


You asked whether the code:

	out("tuple");
	x = inp("tuple");

is guaranteed to set x to 1 (assuming, for the sake of simplicity, that tuple
space is initially empty and that there are no other processes acting on it).
The answer is, "probably".

A better answer is:  Forget about inp and rdp.  They were a mistake that never
belonged in the language; they happened to be trivial to add to a shared-
memory implementation, so snuck in.  But they cause a lot of problems in a
distributed setting, confuse the semantics of the language, encourage the
writing of buggy code, and ultimately add nothing to the expressiness of
Linda.

For arguments justifying these assertions, and a lot of discussion of Linda
semantics, see my dissertation, "Shared Tuple Memories, Shared Memories,
Buses and LAN's - Linda Implementations Across the Spectrum of Connectivity",
available from the Yale Department of Computer Science as TR-714 (July 1989).

(You'll probably get an answer from someone at Yale citing some recent paper
in which a semantics which justifies the conclusion that x = 1 is cited.
Don't take this to mean you should have been able to somehow guess that for
yourself.  Linda went along for years with an early 1960's-style "definition"
with "obvious" semantics that no one ever bothered to write down - until, of
course, what became "obvious" was that different readers (and different
implementors) where finding different "obvious" interpretations.)

Feel free to post a copy of this message to comp.parallel - I have no easy way
of posting to Usenet newsgroups from here.
							-- Jerry