How to free Free OptiX IAS?

[h-OUS-e]

Hello,

I am trying to create a fastAPI app with Mitsuba. The algorithm goes something like this:

1. Read a mesh surface
2. Add mesh surface to a scene dictionary
3. mi.dict_load() the scene dictionary
4. ray trace the scene inside a sample() function with a custom mi.loop()

On the first try, the ray tracing works and a scene is built with Optix on the first mi.Loop():

2023-04-02 01:19:42 INFO  main  [Scene] Building scene in OptiX ..
2023-04-02 01:19:42 DEBUG main  [scene_optix.inl:73] Initialize Optix configuration (index=2)..
2023-04-02 01:19:42 INFO  main  [Scene] OptiX ready. (took 93ms)
Starting loop
Loop Done

But once I get a new mesh surface, and make a new scene to add this new mesh, running the sample() function returns:

jit_eval(): more than one OptiX shader binding table was used within a single kernel, which is not supported. Please split your kernel into smaller parts (e.g. using `dr::eval()`). Disabling the ray tracing operation to avoid potential undefined behavior.

This message doesn't show when I use mi.render(). Looking at the logger, running mi.render() prints [Scene] Free OptiX IAS... I was wondering if I can also free up the Optix IAS inside python with dr.jit to run this custom mi.loop() on the server with updated scenes?

[njroussel]

Hi @h-OUS-e

We don't expose a way to manually delete the OptiX acceleration structures, for good reasons: you might have some variables that depend on it that have not yet been evaluated.
They delete themselves when the scene can be de-allocated. This usually happens as soon as it is no longer referenceable and isn't a dependency of any other variables.

[h-OUS-e]

del scene, or set scene=None didn't work for me, but shouldn't that have made the scene no longer reference-able? What is the right way to de-allocate the scene to free the Optix acceleration structures?

[njroussel]

Yes, but you might have defined a variable that references the scene in its computation before you did del scene.

A tiny example:

a = mi.Float(1)
b = mi.Float(2)
c = a + b
del b # Will not delete b, because c needs it and c is not evaluated
print(c) # Evalutates c and frees b as it no longer referenced by any variable

[h-OUS-e]

I see, I had a sampler outside the web-socket function, and so it wasn't being reset, but now it works thank you! So much magic going on in the backend.