IsaacSim 5.1 hangs with external MDL material loading plus full experience file

Omniverse Isaac Sim
,
1

Isaac Sim Version

5.1.0

Operating System

Ubuntu 22.04

GPU Information

  • Model: RTX 3090
  • Driver Version: 575.64.03

Topic Description

Detailed Description

In IsaacSim 5.1, If I create a material from a MDL file, the simulation will hang when I call sim.reset(), and with full experience file
No such problem in IsaacSim 5.0

Code:

import os
import isaacsim

use_full_exp_file = True
simulation_app = isaacsim.SimulationApp(
    launch_config={"headless": False},
    experience=os.path.join(os.path.dirname(isaacsim.__file__), "apps/isaacsim.exp.full.kit") if use_full_exp_file else "",
)


import omni
from pxr import UsdGeom
from isaacsim.core.api import SimulationContext


def create_minimal_mdl_material():
    stage = omni.usd.get_context().get_stage()
    
    # Get the path to the minimal MDL file
    script_dir = os.path.dirname(os.path.abspath(__file__))
    mdl_path = os.path.join(script_dir, "minimal_test.mdl")
    
    print(f"  MDL file: {mdl_path}")
    print(f"  File exists: {os.path.exists(mdl_path)}")
    
    # Create material
    UsdGeom.Scope.Define(stage, "/World/Looks")
    material_path = "/World/Looks/TestMaterial"
    
    omni.kit.commands.execute(
        "CreateMdlMaterialPrim",
        mtl_url=mdl_path,
        mtl_name="MinimalMaterial",
        mtl_path=material_path,
        select_new_prim=False,
    )
    
    print(f"  ✓ Material created at: {material_path}")


def demonstrate_bug():
    sim = SimulationContext(
        physics_dt=1/60, 
        rendering_dt=1/60, 
        backend='torch', 
        device='cuda:0',
    )
    create_minimal_mdl_material()
    
    print("  ⚠ THIS IS WHERE IT HANGS - IsaacSim will become unresponsive")
    
    sim.reset()
    
    # If we get here, the bug is fixed in your version
    print("  ✓ sim.reset() completed successfully!")

def main():
    demonstrate_bug()

if __name__ == "__main__":
    try:
        main()
    finally:
        simulation_app.close()

minimal_test.mdl:

mdl 1.5;

import ::base::*;
import ::df::*;
import ::anno::*;

export material MinimalMaterial()
[[
    ::anno::display_name("Minimal Material"),
    ::anno::description("Simplest possible MDL material for bug reproduction")
]]
= material(
    surface: material_surface(
        scattering: df::diffuse_reflection_bsdf(
            tint: color(0.5, 0.5, 0.5)  // Simple gray color
        )
    )
);

Additional Information

What I’ve Tried

Switch back to isaac sim 5.0 version, it works.
Or set the use_full_exp_file to false, it works

3

Hi @flm8620
we can reproduce the issue and an internal ticket has been created to track this. Thanks for reporting it!