Segmentation fault in async wrap, if shape has emitter AND bsdf

[georgy95]

Summary

I mainly write asynchronous code, and discovered a bug that results in a segmentation fault.

When a shape has:

• emitter only - works is fine
• bsdf only - works fine
• BOTH - results in a segmentation fault in async wrap only.

System configuration

System information:

OS: 13.2.1
CPU: b'Apple M1'
Python: 3.10.1 (main, Mar 24 2023, 21:25:11) [Clang 14.0.0 (clang-1400.0.29.202)]
LLVM: 16.0.6

Dr.Jit: 0.4.2
Mitsuba: 3.3.0
Is custom build? False
Compiled with: AppleClang 14.0.0.14000029
Variants:
scalar_rgb
scalar_spectral
llvm_ad_rgb

Description

I'd like to be able to render in a non blocking IO way. Currently the scene processes fine if I specify either the emitter or bsdf for the shape. I'm curious why the segmentation fault arises, because it works as expected in sync mode.

Also, I used asyncer library, which seems to work, but can also be the culprit here.

Steps to reproduce

The code below should work as is if you:

• Create the shape
• Provide a path to any image

shape.obj

v  1 -1 -1
v  1  1 -1
v -1  1 -1
v -1 -1 -1
vt 1 0
vt 1 1
vt 0 1
vt 0 0
vn 0 0 1
f 1/1/1 2/2/1 3/3/1 4/4/1

code.py

import mitsuba as mi
mi.set_variant("scalar_rgb")

import anyio
from asyncer import asyncify

PATH_TO_OBJ = ""
PATH_TO_BM = ""

scene = {
    'bsdf_id': {'type': 'diffuse', 'reflectance': {'type': 'rgb', 'value': [0.1, 0.1, 0.1]}},
    "type": "scene",
    "integrator": {
            "type": "path",
            "max_depth": 20,
            "rr_depth": 5,
        },
        "sensor": {
        "type": "perspective",
        "to_world": mi.ScalarTransform4f.look_at(
                    origin=[0,0,4],
                    target=[0,0,0],
                    up=[0,1,0]
                    ),
        "fov": 40,
        'sampler': {
            'type': 'independent',
            'sample_count': 128
        },
        'film': {
            'type': 'hdrfilm',
            'width': 256,
            'height': 256,
            'rfilter': {
                'type': 'box',
            },
            'pixel_format': 'rgb',
        },
    },
    "texture_id": {
        "type": "bitmap",
        "bitmap": mi.Bitmap(PATH_TO_BM),
        "wrap_mode": "clamp",
        "filter_type": "nearest"
    },
    "backwall": {
        "type": "obj",
        "filename": PATH_TO_OBJ,
        "light": {
            "type": "area",
            "radiance": {
                "type": "ref",
                "id": "texture_id"
            }
        },
        "bsdf": {
            "type": "ref",
            "id": "bsdf_id"
        }
    },
    "env": {
        'type': 'constant',
        'radiance': {
            "type": "rgb",
            "value": 1.0
        }
    },
}

scene = mi.load_dict(scene)

async def main():
    await asyncify(mi.render)(scene, sensor=0, spp=10)

anyio.run(main)