Advantages of a large number of threads cf other approaches?
Richard A. O'Keefe
Tue Feb 17 02:55:32 CET 2004
> > * Simulations - why use an object per thread rather than a "classic"
> > OO approach?
> This depends upon the simulation - if you are modeling the real
> world then mapping each concurrent object in the real world with
> exactly one concurrent processes bridges between the gap between the
> model and the simulation code in a very natural way - the code will
> almost "write itself".
I've heard this said before (and have read code samples etc) but I
keep feeling I'm missing something. It's so easy to have all your
objects inherit from a Smalltalk/C++ base class with an update method
and loop through all of them.
No, it's not particularly easy. The two "classic" object-oriented
programming languages that people tend to have heard of are Simula-67
and Smalltalk-72. Now Simula-67 was developed precisely to support
object-oriented simulation. But Simula had TWO key features. OO was
one, and (simulated) concurrency was the other. Simula simulations
basically used co-operative multithreading. Bjarn Stroustrup, who
invented C++, was familiar with Simula 67, and invented it in order to
do the kind of simulations he was familiar with in a C-friendly/Algol-hostile
milieu. Surprise surprise: the Cfront implementation of C++ from AT&T
had TWO key features. OO was one, and (simulated) concurrency was the
other (the Task Library, chapter 2 of the AT&T C++ library manual).
Did I mention that Smalltalk-80 has TWO key features? OO is one, and
(simulated) concurrency is the other.
For what it's worth, there is a software development method called
Jackson Structured Programming, developed years ago and used for serious
EDP systems. One of the ideas in JSP is that you design your program as
a collection of thousands of interacting concurrent processes/objects,
and then "invert" the design to get your COBOL, because you obviously
can't *really* have thousands of concurrent processes (:-).
More information about the erlang-questions