Memory Leak

[Joncom]

I'm working on a Box2D.js plugin for the ImpactJS game engine. Ever since I made this commit, I've been getting this error message:

Uncaught Assertion: Cannot enlarge memory arrays in asm.js. Either (1) compile with -s TOTAL_MEMORY=X with X higher than the current value, or (2) set Module.TOTAL_MEMORY before the program runs.

It happens consistently after 2 minutes of running with about 250 entities. After doubling TOTAL_MEMORY, the error continues to occur, but after 7.5 minutes instead.

Before this commit, I could run the simulation for hours without any issue.

I suspect what's happening here is that instances of b2Vec2 are being created but not destroyed properly, and eventually all the memory is used up. What am I doing wrong here?

---

Here is the new troublesome method being called once per update by every entity:

limitVelocity: function() {
    var velocity = this.body.GetLinearVelocity();
    var x = velocity.get_x() / Box2D.b2SCALE;
    var y = velocity.get_y() / Box2D.b2SCALE;
    if(x < -this.maxVel.x)     x = -this.maxVel.x;
    else if(x > this.maxVel.x) x = this.maxVel.x;
    if(y < -this.maxVel.y)     y = -this.maxVel.y;
    else if(y > this.maxVel.y) y = this.maxVel.y;
    x *= Box2D.b2SCALE;
    y *= Box2D.b2SCALE;
    this.body.SetLinearVelocity( new Box2D.b2Vec2(x, y), this.body.GetPosition() );
}

[Joncom]

Found some useful info here:

JavaScript, specifically ECMA-262 Edition 5.1, does not support finalizers or weak references with callbacks. Thus, JavaScript code must explicitly delete any C++ object handles it has received. Otherwise the Emscripten heap will grow indefinitely.

With that in mind, I realized that I was creating new b2Vec2 instances, but never destroying the original one. I'm so used to letting the JavaScript garbage collector do that for me.

So instead of creating a new b2Vec on the last line, I re-used the one that already exists:

velocity.set_x(x);
velocity.set_y(y);
this.body.SetLinearVelocity( velocity, this.body.GetPosition() );

Perfect!

[jagenjo]

But is it possible to delete from Box2D the references we no longer need? because reusing is dangerous, I dont know if the reference I passed to box2D is being used internally so any changes could affect existing objects on the scene. I guess I could check if the functions use copy, reference or pointer for every call, but maybe there is an easier way to free memory.

[kripken]

destroy should free the C++ side of things.

On Thu, Jul 18, 2013 at 6:10 AM, jagenjo notifications@github.com wrote:

But it is possible to delete the references we no longer need? because reusing is dangerous, I dont know if the reference I passed to box2D is being used internally so any changes could affect existing objects on the scene.

— Reply to this email directly or view it on GitHubhttps://github.com/kripken/box2d.js/issues/27#issuecomment-21181935 .