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Re: [Bug-gnubg] Threaded rollouts and RNGs

From: Ian Shaw
Subject: Re: [Bug-gnubg] Threaded rollouts and RNGs
Date: Fri, 3 Feb 2017 13:42:12 +0000

Hi Øystein,


My understanding, which is very old, is that it is threaded on the rollout candidates. In-game move evaluations are not threaded.


But Phillippe has done a lot of work since then ,so it may have changed.


n  Ian


From: Bug-gnubg [mailto:bug-gnubg-bounces+address@hidden On Behalf Of Øystein Schønning-Johansen
Sent: 01 February 2017 10:11
To: address@hidden
Subject: [Bug-gnubg] Threaded rollouts and RNGs




It's a long time since I browsed the GNU Backgammon code now. :-)


The rollout code in GNU Backgammon is of course threaded. How is this threaded actually? Is it threaded on each sample (aka each game). One thread pr. game? Or one thread pr. evaluation? Or?


I just wrote a code that does a threaded MC simulation of a different problem, and I noticed that I got significantly different results depending on either I used threading or not. Funny thing, it didn't initially occur to me, but of course I need one separate RNG instance for each thread. Fixing that didn't only give me the right results of the simulation, but it also improved the performance.


How about GNU Backgammon? Do you use one separate RNG instance for each thread?


best regards,



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