From: Michael Neumann <neumann@...>
Date: 2001-11-30T08:28:15+09:00
Subject: [ruby-talk:26997] Re: Can someone explain TupleSpaces?

Phil Tomson wrote:
> I looked at the examples that came with drb, but I'm still not quite 
> grok'ing TupleSpaces.  
> 
> First of all, what is the Tuple?  It seems to be a list of three items 
> (though I've seen more in some of the lists) - is it a way of calling a 
> method on a remote object by passing in an array of items with the first 
> element being the name of the method? (that's the theory I came up with 
> after looking at the examples - but I could be way off).

Tuples come from mathematics. Unlike lists they have a predefined length. 
For example (1,2,3) is a 3-tuple, (1,"string",:3,4) a quadruple etc.

A TupleSpace is a place where you can store arbitrary tuples. 
Two operations are defined on it:

  - put a tuple into the TupleSpace
  - get/remove a tuple (poss. specified by a pattern) from the TupleSpace
  
Both operations are performed atomic (thread-safe). 


Suppose you have a server thread A and a client thread B. 

Thread A calls the "get" method accepting tuples matching ("add",_,_)
where _ is a placeholder for any value. Method "get" waits until a
matching tuple appears in the TupleSpace. 

The client thread B now wants to add two numbers. Therefore it puts a
tuple ("add",2,3) into the TupleSpace. After that it waits for a tuple
matching ("result",_).

Now thread A returns from method "get", because a matching tuple
("add",2,3) exists, and removes this tuple. In response it puts
a tuple ("result", 5) back into the TupleSpace.

Thread B gets now active again and removes the tuple ("result",5) from
the TupleSpace. 

> I guess I'm looking for the 50000ft view of TupleSpace... and can someone 
> tell me why I would use them?

With this architecture you can very easy communicate and synchronize between different
threads or processes. 

Regards,

  Michael


-- 
Michael Neumann
merlin.zwo InfoDesign GmbH
http://www.merlin-zwo.de