PEP: XXX
Title: Logic Variable Thread Synchronization
Version: $Revision: 1.9 $
Last-Modified: $Date: 2002/08/26 16:29:31 $
Author: James A. Bowery <janotboweryfor@spamearthlink.net>
Discuss-To: stackless@www.tismer.com.
Status: Draft
Type: Standards Track
Requires: 219
Content-Type: text/plain
Created: 16-May-2003
Python-Version: 2.4
Post-History:


Abstract

    Stackless Python [1] is an ideal environment within which to
    implement logic variables for thread synchroniziation [2].
    The 3 additions required for this are 1) the addition of the
    "unknown" keyword that declares a logic variable, 2) the
    "final" keyword that declares a logic variable to be single-
    assignment and 3) the "=:=" operator that performs a 
    unification of a logic variable with an expression.


Rationale

    Stackless Python promises to deliver microthreads.

    The semantics of threaded computations are unnecessarily complex.
    
    Logic variables can replace virtually all other synchronization
    semantics with the simple and intuitive notions of data flow.
    Furthermore, implementations of logic variables are stackless.

    While logic variables can be used to implement logic programming,
    logic programming is not required for the implementation of
    logic variables.

    For a full description of the benefits of logic variables in
    distributed concurrent constraint programming, see the paper 
    "Efficient Logic Variables for Distributed Computing" [2].

    For a description and examples of the new language features 
    required: "unknown", "final" and "=:=", see Section 2.5.1 [ibid].


References

    [1] PEP 219, Stackless Python, McMillan
        http://www.python.org/peps/pep-0219.html

    [2] Efficient Logic Variables for Distributed Computing,
        by Haridi,van Roy, Brand, Mehl, Scheidhaur and Smolka 
        http://www.mozart-oz.org/papers/abstracts/TOPLAS99.html


Copyright

    This document has been placed in the public domain.



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