Re: Multithreading question

[Gregory R Madey]

Matteo,

Any chance we will see you in Notre Dame this spring?

I've arranged for John Holland to be the keynote speaker!

http://www.nd.edu/~swarm03/

Would you be interested in giving a talk on multi-theading Swarm
simulations?

Grg


On Wed, 29 Jan 2003, Matteo Morini wrote:

> Dear Darold,
> 
> together with some of my colleagues we're investigating the possibility 
> of running multithreaded Swarm applications on multiple processors. Our 
> idea would be to exploit a Mosix cluster; if I understand correctly you 
> are thinking about multiprocessor machines, but in the end we're 
> tackling the same issue.
> 
> With Javaswarm we're stuck (the problem being with mosix anyway, not 
> with multiprocessor pc's). I personally have an Objective-C application 
> which would benefit a lot from going multithreaded (either on Mosix or 
> on a multiprocessor single machine), being inherently parallel. It's 
> about a genetic algorithm-based production planner: if you're into GAs 
> you've probably seen the point already. The fact is many computationally 
> heavy independent tasks (computing every candidate solution's fitness) 
> can be run simultaneously on different CPUs. The idea of going 
> multithread has been in my mind for a long time, and I expect to start 
> working on it seriously as soon as I get some spare time. By now I've 
> just got a really simple Obj-C Swarm multithreaded application 
> performing dummy tasks in parallel. I can send it to you if you feel 
> like giving it a look.
> I did go multithread by scheduling the independent steps like this 
> (untested pseudocode follows :-)
> I'm going by memory... sorry for errors)
> 
> [modelActions createActionForEach: agentsList message(step1)]
> [modelActions createActionForEach: agentsList message(step2)]
> 
> where each anAgent in agentsList performs:
> 
> *at step 1:
> 
> {...
> 
>     mypid=fork();
>     if mypid=0 {
>         //pid=0 tells you this is a child
>         //perform task
>         //store result somewhere (*)
>         return self; //(or was it exit 0?)
>     }    else
>     return self; //this is the parent process, return immediately and 
> spawn next child
> }
> 
> *at step 2;
> 
> {...
>     waitpid(mypid,NULL,0);
>     //in order to keep things in sync we wait for all the agents in list 
> to perform before starting a new cycle
>     return self;
> }
> 
> (*) managing to catch 'child' processes results is not so easy: I'm 
> trying shared memory (but this would not go on Mosix) or writing to file.
> 
> Answering your questions: converting your application to multithread 
> would definitely not kill you *if* it has a parallel architecture, that 
> is there is something that can be done without waiting for the previous 
> step to complete. In other words (and keeping it as simple as it can): 
> if your problem is to solve (a+b) * (c+d) you can split the problem into 
> (a+b) and (c+d) and run the two sub-problems on different processors, 
> then multiply the results. If  you need to recursively solve an equation 
> like x(t+1)=f(x(t)) you see you can't do the trick, and are bound to 
> serially perform each step, since you have to wait for the last 
> iteration to complete before moving on. This would not kill you either 
> but would waste a lot of your time.
> Without making your application mulithread you'd have a monolithic 
> process running on a single processor; I bet that's not you expect from 
> a 4-way hyperthreaded P4 :-)
> 
> ---Matteo
> 
> Darold Higa wrote:
> 
> >I have done very little research on this topic, but I do know my simulation
> >has serious performance issues.  I am looking into a new development
> >platform.  I was told by someone that if I wanted to look into
> >multithreading, the libraries that I'm building from have to be
> >multithreading compliant.  Do the Swarm libraries meet this criteria?  I
> >vaguely recall parallel processing as one possible direction for swarm.
> >
> >It seems that the two leading contenders hardware wise are Apple desktops
> >and a P4 system with Hyper Threading, both are multiprocessor setups (albeit
> >virtual in the P4 case).  Either system would benefit from multithreaded
> >applications, if I understand correctly.
> >
> >Is it going to kill me to convert my ObjC Swarm app into a multithreaded
> >application?  Will I see any real benefits even without making the
> >application multithreaded?
> >
> >So many hardware related questions, I apologize.
> >
> >Darold Higa
> >
> >
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>                   ==================================
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> 

                  ==================================
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   to day usage of Swarm.  For list administration needs (esp.
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   with "help" in the body of the message.