Isaac Sim 5.1.0 Async Rendering in Standalone Python App

[alangshur]

Overview

We're using Isaac Sim 5.1.0 in a standalone Python workflow where we manually control physics stepping and rendering. We use World from isaacsim.core.api and step physics at variable rates while rendering adaptively based on performance:

from isaacsim.core.api.world import World

world = World(
    physics_dt=0.001,  # Variable, changed dynamically
    rendering_dt=0.01667,
    backend="numpy",
)

# Main loop
def step(self, dt: float):
    # Step physics
    physics_context.set_physics_dt(dt=dt)
    world.step(render=False)
    
    # Handle application logic
    self._process_operations()
    
    # Render when needed
    if should_render:
        world.render()  # Blocks up to 30-40ms sometimes

The Problem: Since everything runs in a single thread, our physics/logic loop is blocked by world.render() calls that take 30-40ms on an RTX 6000 Pro for complex scenes. If rendering could happen asynchronously in a background thread, our simulation could maintain target speed much more easily.

What We Tried

The new async rendering feature from Isaac Sim 5.1.0, which we've enabled in both SimulationApp and the carb settings:

kit = SimulationApp(
    launch_config={
        "extra_args": ["--/exts/isaacsim.core.throttling/enable_async=true"]
    }
)

import carb
settings = carb.settings.get_settings()
settings.set("/exts/isaacsim.core.throttling/enable_async", True)

When we benchmarked render performance with async enabled vs disabled, we didn't see a difference. It doesn't appear to be working in our Python standalone workflow.

Questions

1. Does async rendering work during active physics stepping (world.is_playing() == True), or only when stopped/paused?
2. Does it require additional API changes beyond the setting to make world.render() non-blocking?
3. The docs state it "is only set true when running with isaacsim.exp.full.kit, not when running via a Python-based workflow." Does this mean it fundamentally doesn't work in Python apps?

Environment: Isaac Sim 5.1.0, Python 3.11, RTX 6000 Pro, Ubuntu 24.04

Any guidance would be appreciated!

[vick-yu]

Thanks for raising this and for your detailed performance investigation.

To clarify, the /exts/isaacsim.core.throttling/enable_async setting is intended to enable async rendering only on stop/pause. This is why no difference is seen during active runtime—it's part of the throttling extension and is designed to speed up UI interaction, not live simulation workflows. While you can enable this in Python workflows, it will only activate async rendering behavior when the simulation is stopped or paused.