[erlang-questions] OpenPoker v2: The bestest and most scalable poker server ever

Jean Sagi jeansagi@REDACTED
Thu Oct 30 13:24:47 CET 2008

Isn't it said that perfection is achieved when there is nothing left to take
away ;)


2008/10/29 Joel Reymont <joelr1@REDACTED>

> http://tinyurl.com/5exq4c
> This is the final architecture as I'm sick of rewriting the thing and
> I don't think I can simplify it further!
> The first version I wrote back in 2005 used processes for everything.
> Seats, games, players, bots, games, pots, hands, all were processes.
> Moreover, they were all gen_servers.
> My cardgame "uber gen_fsm" was of particular interest and gave me the
> ability to put a stack of gen_fsm modules together. The cardgame
> driver would pop modules off the stack as they finished and modules
> could also tell the driver to re-run them, restart from the top of the
> full stack or go to the last module.
> The implementation was fugly but gave me the ability to put card game
> logic together from a set of betting, card dealing, etc. modules.
> Texas Hold'em, for example, uses a stack that looks like this:
> wait_for_players, blinds, deal_cards, betting, deal_cards, etc.
> Another feature was mapping process ids to integers by using
> gen_server:call on the pid at serialization time and looking up the
> integer in Mnesia when interpreting the packets.
> Last but not least, games freely gen_server:called players and vise
> versa, a recipe for disaster as I discovered under very high load.
> Yes, Virginia you can deadlock in Erlang!
> A great example of deadlock waiting to happen is firing off a timer
> from a game process and asking the player process for its id while the
> player is waiting for something from the game after a gen_server:call
> of its own.
> There are only two process types left in this latest version of
> OpenPoker: games and players. State machine logic is integrated into
> the game gen_server and I'm happy to say that the implementation is
> beautiful and still uses a stack of modules, albeit much smaller and
> simpler.
> Game gen_servers never ever call players and all processes are
> globally registered as {game, N} and {player, N} respectively. All
> packets go out with the integer ids in them since they are known at
> the source. Incoming messages are simply addressed to {player,
> <integer id}. This works, scales and is darn fast! It does rely on the
> "global" infrastructure but it hasn't let me down yet.
> Everything else is just record "mutation", no message passing
> whatsoever.
> I'm throwing down the gauntlet here. I'll bloody switch to Lisp and
> libevent-based single-threaded servers if this OpenPoker cannot handle
> mover than 10k games and 50K players on a single server!
> --
> wagerlabs.com
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