[erlang-questions] game engines?

Daniel Goertzen <>
Tue Sep 20 16:42:57 CEST 2016


Erlang processes shine when they can run asynchronously and in a loosely
coupled manner, so I am skeptical that a process-per-entity would work well
where the entities need to run synchronously (20 times/sec) and interact
heavily.  For synchronous, interactive behavior I suspect the solution you
currently have (thread iterating through objects) is simplest.

I remember a discussion years ago about a simulation consisting of ants
randomly moving from square to square on a chess board where only 1 ant is
permitted on a square.  The discussion revolved around process-per-ant and
all the synchronization issues that it entailed.  It turned out that
flipping things inside out and using a process-per-*square* and
representing the ants as messages passed between them worked out much
better.  There are many ways to use processes, and mapping them to your
simulation's actors is not always best.  Is there another way to apply many
processes to a military sim?


On Mon, Sep 19, 2016 at 10:55 AM Miles Fidelman <>
wrote:

> Thanks to all for your responses.
>
> Re. a couple of points here, might I ask a few follow-up questions:
>
>
> On 9/18/16 1:37 PM, Lutz Behnke wrote:
>
> Hello,
>
> assigning each object in the game gets difficult for a number of reasons,
> when trying to do this for an MMO, especially MMORPGs (characterized by a
> very large number of objects, and active entities):
>
> You waste resources (CPU, RAM) when an object is currently not being
> referenced by an active entity (e.g. a client connection, thus and avatar
> or alternatively a Mob/NPC), since there is no other process that will send
> any messages.
>
>
> Well yes, but is that not where Erlang shines - being able to maintain
> huge numbers of processes (or, in this case, little state machines)?
>
>
>
> More importantly, should you scale your engine to multiple hosts, you
> either have to enforce a single process, requiring all updates and query
> messages to be routed to this proc. Or you will have to build some
> master/slave or peer to peer logic, which will ensure consistency in the
> face of CAP.
>
>
> I'm actually thinking about military simulation - where the model is
> essentially:
>
> - every simulator (e.g., a flight sim, or a tank) is running on its own
> machine, complete with local world model and image generation (necessary to
> keep up with jitter-free image generation during high-g turns - you don't
> want pilots to puke all over the simulators)
>
> - there's a lot of dead reckoning going on locally - the only things that
> cross the network are deltas and events, generally sent by multicast
>
> - everything is synchronized by GPS time-stamp
>
> I discovered Erlang when I realized that we (the company I worked for)
> took a very different approach for simulating "virtual forces" (think
> non-player characters) - when we simulated 1000 tanks, on one machine, each
> tank would be an object, and we had 4 threads winding their way through
> every object, 20 time a second.  Turns out that the main loops are real
> spaghetti code that breaks every time a new property gets added to an
> object.
>
> I started wondering why we didn't just have a process per simulated object
> - essentially the way we treated the person-in-the-loop simulators.  The
> answer, of course, being context switching overhead.
>
> Then, I discovered Erlang.  And I started thinking - why not just have a
> process per object.
>
>
>
> Separating into a) the state of instances, which you can store in a
> KV-store and have b) a pool of generic procs, that will process the state
> with c) a set of modules that provides the logic for a particular object
> allows to push the state to the appropriate host. With a separate KV-store
> that can handle net-partition and node failure, you gain even a good amount
> of fault-resilience.
>
> Please excuse me beating my own drum, but I have implemented a prototype
> of such an engine (
> http://dl.acm.org/citation.cfm?id=2577389&CFID=787355984&CFTOKEN=91169762).
> Unfortunately, for legal reason, I cannot make the code publicly available
> yet.
>
>
> Any chance of arranging a copy that's not behind a paywall?
>
>
> Thanks,
>
> Miles
>
>
>
> mfg lutz
>
> Am 18.09.2016 um 04:11 schrieb Miles Fidelman:
>
> Hi Folks,
>
> I'm curious, has anybody written an Erlang-based game engine that
> implements a process per game entity?
>
> I've been been finding various examples of Erlang being used to manage
> user sessions, and other aspects of MMORPGs - but nothing that simply
> does the obvious - treating each object, player, etc. as an Erlang
> process.
>
> Am I missing something?
>
> Thanks,
>
> Miles Fidelman
>
>
>
>
>
>
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>
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> In practice, there is.  .... Yogi Berra
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