Multithreading in JavaScript for game development

Question

I am thinking of developing a game in pure JavaScript and html5, without using any third party plugins. The problem I am facing is that I cannot find a way to separate different "modules" of the game into separate threads, like the render job, game logic, asset loading and so on.

Web Workers seem to be able to separate code into different threads, but the problem with them is the limited information I can pass between them. For example, for the render job, I need to pass the whole "world", with all the entities, meshes, textures and so on for every update of the game, because worker threads cannot share memory. It can be optimized, like sending the static objects only on initialization (meshes, textures) and then send only the state of an object on update (it's world transform) but it still isn't desirable.

Is there a way to send large data between them or have them share some objects? Or is there a different method entirely of achieving true multithreading? I know there are easier ways of achieving this using plugins/ gears but I need to use only methods available in open web;

While not taking away anything from the validity of asking for "real" parallelism with Javascript, the way you ask the question leads me to recommend to you to read up on the event based programming model. As an example (for software using that model, yes neither's written in JS), the event-based nginx webserver outperforms the thread-based Apache by far, especially under heavy load. Just to give an example that NOT using those more traditional means of parallelism is partially intentional in Javascript, and to explain why "webworkers" are still not widely available/used. — Mörre
– Mörre, Commented Jun 14, 2011 at 20:09

Cat Chen · Accepted Answer · 2011-06-15 03:04:17Z

6

JavaScript's Web Worker is a better concurrent programming model in some way. For example, it's event driven and there's no shared object. This means you can't get into grid lock (because there's no lock at all) and an object can't get into invalid state by being modified by two threads at the same time.

The problem is you can't easily stack traditional game system on the top of this model. So you need to design the game system in a new way to adopt this programming model, and I think this might be costly.

answered Jun 15, 2011 at 3:04

Cat Chen

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Jon Erickson · Accepted Answer · 2011-06-14 20:02:58Z

4

You probably want to look into Web Workers, I have no experience with them but have heard of them. Might lead you into the right direction.

http://ejohn.org/blog/web-workers/

answered Jun 14, 2011 at 20:02

Jon Erickson

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2 Comments

Colin Dumitru Over a year ago

By worker threads I meant Web Workers. I made a small edit to clarify this. Like I said, workers seem to be able to achieve multithreading, but there are problems with the way I can share information between them.

Mörre Over a year ago

Well, there IS nothing else. JS's first method to run things in "parallel" is event based programming. This of course only uses one CPU (-core) but within that limit scales tremenduously well. The pretty recent addition of webworkers (as far as real-world availability is concerned) is the only practical method thus far to scale beyond once CPU (core) with one piece of (JS) software.

gion_13 · Accepted Answer · 2011-06-14 20:05:32Z

0

web-workers are the closest thing to multithreading in js.
At the moment.
Full stop.

answered Jun 14, 2011 at 20:05

gion_13

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Comments

MillsJROSS · Accepted Answer · 2011-06-14 21:45:44Z

Sans Web Workers there's no real way to do multithreading in javascript that I know of.

You could use some logic to prioritize how much time should be spent doing certain tasks, though. You could make functions that store information in states (so loops could be exited and then picked back up at a later time). Each loop just knows how much time it has before it saves it's state and exits the function.

So the for loop would have a time condition, too...

//Loop over some iterator, exit if time is up
for (i = 1; i < max || timeNotUp(); i++)
{
}

//If exiting normally 
if (i == max)
{ //do somthing
}
//otherwise, save state
else
{
    this.i = i;
    this.otherStuff = otherStuff;
}

You can definitely prioritize your code this way. But, there are downsides. Saving your state doesn't lead to clean easy to follow code (especially with loops within loops). It also isn't as fast, since you're constantly checking time and saving states.

thSoft · Accepted Answer · 2011-07-27 17:01:07Z

0

I recommend a functional approach for composing the aspects of your game. See e.g. http://www.flapjax-lang.org.

answered Jul 27, 2011 at 17:01

thSoft

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