Computer Chess Club Archives




Subject: Re: Parallel algorithms in chess programming

Author: Vincent Diepeveen

Date: 05:00:27 04/17/01

Go up one level in this thread

On April 16, 2001 at 22:07:10, Robert Hyatt wrote:

>On April 16, 2001 at 18:15:52, Dieter Buerssner wrote:
>>In a different discussion, Vincent wrote the following:
>>>It is not difficult to implement the form of parallellism as used by
>>>Rudolf. Invented by a frenchman who couldn't spell a word english and
>>>who wrote an impossible article for JICCA (did anyone proofread it at
>>>the time as i'm pretty sure they didn't get his parallel idea?).
>>>At the time when i read the article i was pathetically laughing about it
>>>actually as i also didn't get the idea of the frenchman. But it appears
>>>everyone who can make a chessprogram work under win2000 can also get
>>>within an afternoon his program parallel to work. Then some debugging
>>>and a day later it works cool.
>>I'd be very interested in this algorithm, that can be implemented at an
>>afternoon :-)
>>Could you point elaborate on this.
>>BTW. In Paderborn, Roland Pfister also told me, that he knows this from Rudolf
>>Huber, and he even started to explain it to me. Somhow, we (or me) got
>>distracted, and I cannot remember the essential things.
>>What I remember is, that the time consuming work, of making your
>>search/evaluation routines free from all those global variables is not needed.
>Global variables will _always_ be a problem.  Unless you avoid threads
>altogether and use separate processes.  But then you incur other penalties
>you have to solve...

Multiprocessing is faster anyway of course as multithreading as i
do not need to read a stupid pointer.

Arrays which are only read and not modified one can put in shared memory
and read from there without penalties.

The penalty for multithreading is, when using ansi-c conventions,
way bigger as for multiprocessing.

Multiprocessing is more than ok.

Obviously it's not always so easy to get it to work, because of
different causes
  - allocating shared memory in linux isn't simple
  - windows NT server/tuple server versions have the bad habit
    to always swap away shared memory to the cache when the allocated
    memory size is huge.
  - to share memory in NT in such a way that programs have the same
    virtual adress space is not evident, as there are 2 functions which
    one can use and one of them is not going to work for you. Don't need
    to mention that by accident i picked the wrong function initially :)

Of course all the above problems are solvable

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