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<p>On 9/20/16 10:42 AM, Daniel Goertzen wrote:<br>
</p>
<blockquote
cite="mid:CAJCf5RzwJi-5upJ4xwFhNrZgsPmABHZo67jmT-gBK3BFYS8oGw@mail.gmail.com"
type="cite">
<div dir="ltr">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.<br>
</div>
</blockquote>
<br>
I'm not actually sure that you'd need to run items synchronously in
an actor based design. <br>
<br>
1. Anything that's not doing anything can simply suspend itself
until an incoming message triggers a state change. That saves a LOT
of cycles right there.<br>
<br>
2. For things that are moving, I'm not sure how distributing time
ticks to x000 processes, and then letting them do their thing, is
any different than iterating through the same x000 processes.<br>
<br>
What gets tricky, in any case, is line-of-sight calculations, and
behaviors that are based on what each object sees. That requires
some form of global state, and operations on global state. But
that's a separate issue, and one that one also has when threading a
chain of control through a bunch of objects - either way, one either
has to do a global calculation, or each entity has to take a look
around itself.<br>
<br>
<blockquote
cite="mid:CAJCf5RzwJi-5upJ4xwFhNrZgsPmABHZo67jmT-gBK3BFYS8oGw@mail.gmail.com"
type="cite">
<div dir="ltr"><br>
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?<br>
</div>
</blockquote>
<br>
Now isn't that an interesting thought!<br>
<br>
Miles<br>
<br>
<blockquote
cite="mid:CAJCf5RzwJi-5upJ4xwFhNrZgsPmABHZo67jmT-gBK3BFYS8oGw@mail.gmail.com"
type="cite">
<div dir="ltr"><br>
<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, Sep 19, 2016 at 10:55 AM Miles Fidelman
<<a moz-do-not-send="true"
href="mailto:mfidelman@meetinghouse.net">mfidelman@meetinghouse.net</a>>
wrote:<br>
</div>
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<div bgcolor="#FFFFFF" text="#000000">
<p>Thanks to all for your responses.</p>
<p>Re. a couple of points here, might I ask a few
follow-up questions:<br>
</p>
</div>
<div bgcolor="#FFFFFF" text="#000000">
<p><br>
</p>
<p>On 9/18/16 1:37 PM, Lutz Behnke wrote:<br>
</p>
<blockquote type="cite">Hello, <br>
<br>
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): <br>
<br>
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. <br>
</blockquote>
<br>
</div>
<div bgcolor="#FFFFFF" text="#000000"> Well yes, but is that
not where Erlang shines - being able to maintain huge
numbers of processes (or, in this case, little state
machines)?</div>
<div bgcolor="#FFFFFF" text="#000000"><br>
<br>
<blockquote type="cite"> <br>
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. <br>
</blockquote>
<br>
</div>
<div bgcolor="#FFFFFF" text="#000000"> I'm actually thinking
about military simulation - where the model is
essentially:<br>
<br>
- 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)<br>
<br>
- 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<br>
<br>
- everything is synchronized by GPS time-stamp<br>
<br>
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.<br>
<br>
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.<br>
<br>
Then, I discovered Erlang. And I started thinking - why
not just have a process per object.</div>
<div bgcolor="#FFFFFF" text="#000000"><br>
<br>
<blockquote type="cite"> <br>
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. <br>
<br>
Please excuse me beating my own drum, but I have
implemented a prototype of such an engine
(<a moz-do-not-send="true"
href="http://dl.acm.org/citation.cfm?id=2577389&CFID=787355984&CFTOKEN=91169762"
target="_blank">http://dl.acm.org/citation.cfm?id=2577389&CFID=787355984&CFTOKEN=91169762</a>).
Unfortunately, for legal reason, I cannot make the code
publicly available yet. <br>
</blockquote>
<br>
</div>
<div bgcolor="#FFFFFF" text="#000000"> Any chance of
arranging a copy that's not behind a paywall?<br>
<br>
<br>
Thanks,<br>
<br>
Miles<br>
<br>
<br>
</div>
<div bgcolor="#FFFFFF" text="#000000">
<blockquote type="cite"> <br>
mfg lutz <br>
<br>
Am 18.09.2016 um 04:11 schrieb Miles Fidelman: <br>
<blockquote type="cite">Hi Folks, <br>
<br>
I'm curious, has anybody written an Erlang-based game
engine that <br>
implements a process per game entity? <br>
<br>
I've been been finding various examples of Erlang
being used to manage <br>
user sessions, and other aspects of MMORPGs - but
nothing that simply <br>
does the obvious - treating each object, player, etc.
as an Erlang process. <br>
<br>
Am I missing something? <br>
<br>
Thanks, <br>
<br>
Miles Fidelman <br>
<br>
<br>
</blockquote>
<br>
<br>
<br>
<fieldset></fieldset>
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</blockquote>
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<blockquote type="cite">
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In practice, there is. .... Yogi Berra</pre>
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