From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2001-11-30T08:55:42+09:00
Subject: [ruby-talk:27001] Re: Can someone explain TupleSpaces?

In article <m28zcp2n6x.fsf@zip.local.thomases.com>,
Dave Thomas  <Dave@PragmaticProgrammer.com> wrote:
>ptkwt@shell1.aracnet.com (Phil Tomson) writes:
>
>> First of all, what is the Tuple?
>
>It's a slightly bad name :)
>
>A tuple is an array of values, capable of being stored in tuplespace.
>
>A tuplespace is a (potentially distributed) big bag-o-tuples.
>
>A tuplespace has three basic operations:
>
>- out: store a tuple
>- in:  get a tuple (removing it from the tuplespace)
>- rd:  get a tuple, leaving it in the tuplespace
>
>The magic happens in the 'in' and 'rd' methods, because they perform
>pattern matching: just like reading a row from a database, you can
>specify a pattern, and the tuplespace will return some arbitrary row
>that matches the pattern (waiting until one does it there's not one i
>the tuplespace).
>
>So, say we have a communal tuplespace that records what mp3 each of us
>is listening to. I could store the track title, indexed under my name,
>using something like:
>
>   ts.out [ 'dave', track ]
>
>Someone 10,000 miles away could find out what I was listening to using
>
>   name, track = ts.rd [ 'dave', nil ]
>
>The pattern here is the parameter to #rd: it's a template for the
>tuples I'm prepared to accept back from the read, in this case all
>those with 'dave' as the first value and an arbitrary second
>parameter.
>
>Now, when my mp3 player changes tracks, I want to update my listing. I
>could do something like:
>
>  ts.in [ 'dave', nil ]       # delete old entry
>  ts.out [ 'dave', track ]    # add new one
>
>Typically, though, you implement higher level protocols on top of
>tuplespaces using these basic operations.
>
>One of the neat things about Ruby's implementation of tuplespaces is
>that the matching of tuples is done using an element-by-element test
>using the === operator. That means you can do things like
>
>  ts.rd [ /^D/, nil ]     # read a tuple for someone whose name starts
>                          # with a D
>
>  ts.rd [ nil,  JazzSong ] # return a tuple that has a JazzSong
>                           # object in the second parameter
>
>(and, abandoning the mp3 tuplespace)
>
>  ts.rd [ nil, 21..35, :male, /usa|canada/i ]
>                          # return an entry for a person whose age is
>                          # between 21 and 35, who is male, and
>                          # whose address is in canada or the us.

OK, from your description a TupleSpace sounds like a datastructure that 
acts almost like a database - am I correct or is it more of the "blind man 
enounters the elephant" speculation?  And using rinda you can distribute 
the TupleSpace over a network, correct?

>
>Fun, eh?
>
Sounds interesting and it's starting to sound useful.
I think I'll have to play with the actual code to figure it out...

Phil