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kripken / ammo.js

Direct port of the Bullet physics engine to JavaScript using Emscripten
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Memory leaks when destroying objects. Remaining __cache__ references? #284

Open Maksims opened 4 years ago

Maksims commented 4 years ago

We've been using ammo.js in https://github.com/playcanvas/engine and recently I were going through some memory leaks related to ammo.js. Everything has to be manually cleared, but there are certain references left in ammo.js __cache__ objects.

Here are few examples:

  1. creating btRigidBody, then get use getMotionState on it. Then Ammo.destroy(body), but motionState will remain in Ammo.btMotionState.__cache__. Calling Ammo.destroy(state) on it, will throw an error, as I would assume it is actually destroyed already with body, but reference still in present.

  2. Creating btCollisionShape, of different types, like btBvhTriangleMeshShape. Calling Ammo.destroy(shape) removes shape, but leaves btBvhTriangleMeshShape in Ammo.btBvhTriangleMeshShape.__cache__.

  3. btDefaultMotionState, when related btMotionState is destroyed, it does not remove related Ammo.btDefaultMotionState__cache__.

  4. Calling manifold.getBody0 or manifold.getBody1, will return btCollisionObject, but then references to it, never removed as well, when that object is eventually destroyed by Ammo.destroy(rigidBody).

How do we properly remove those related __cache__ references, when their actual objects are destroyed internally? Doing: delete Ammo.btBvhTriangleMeshShape.__cache__[shape.ptr]; seems very hacky.

kripken commented 4 years ago

Thanks, this does sound like a bug. I opened https://github.com/emscripten-core/emscripten/issues/9854 in emscripten, with an idea for how to avoid it.

lm165678 commented 4 years ago

Hi, can someone help me? When I use ammo to create a large number of btbvhtrianglemeshshapes, if the number of meshes is too large, I will report oom. But I don't know how.

I have 10473 solid objects, 877308 vertices and 292436 triangles. I hope to solve this problem without reducing the number of grids, because this is a BIM project.

lm165678 commented 4 years ago

When creating the btbvhtrianglemeshshape of the 7000th entity, it will report oom. When you directly treat the whole scene as a btbvhtrianglemeshshape, it will directly oom. So I divided it into more than 10000 btbvhtrianglemeshshapes.

Maksims commented 4 years ago

Sorry for offtopic, but 10k physical objects, is definitely an overkill for a web browser. With such numbers of objects and triangles, you will want to move towards native platforms, and think of optimising an approach. As even for native, it will be a struggle.

lm165678 commented 4 years ago

Sorry for offtopic, but 10k physical objects, is definitely an overkill for a web browser. With such numbers of objects and triangles, you will want to move towards native platforms, and think of optimising an approach. As even for native, it will be a struggle.

Thank you for your reply. It seems that I can only use game like solutions to solve physical simulation on BIM..

lm165678 commented 4 years ago

Sorry for offtopic, but 10k physical objects, is definitely an overkill for a web browser. With such numbers of objects and triangles, you will want to move towards native platforms, and think of optimising an approach. As even for native, it will be a struggle.

Hi, I solved my problem and made sure the frame rate of both the renderer and the physical engine is 60. For non wasm versions. That is, the ammo.js file. Before importing ammo.js, add the statement "var Module = {TOTAL_MEMORY: 512 1024 1024};" to allocate the total memory. In the official case, it seems that modifying the total memory has no effect, and the memory still leaks. So I modified the ammojs file and added the code: "d.TOTAL_MEMORY = Module ? Module.TOTAL_MEMORY : null;" and then I succeeded. I hope I can help you. In addition, for bvhtrimesh, if too many physical engines are created, the frame rate is relatively low. But if you combine the mesh into one, even millions of vertices and triangles, the physics engine on my laptop is still 60 frames.