How can I implement multiple viewers for different simulations? #2429

HoangGiang93 · 2025-02-16T20:33:44Z

HoangGiang93
Feb 16, 2025

Intro

Hi!

I am a researcher at Institute for Artificial Intelligence, University of Bremen, I use MuJoCo for my research.

My setup

MuJoCo version: 3.2.7
API: Python
OS: Ubuntu>=20.04

My question

I am attempting to implement multiple viewers, with each viewer operating in a separate process and linked to a distinct simulator. I've experimented with both multiprocessing and threading approaches. While multiprocessing allows each viewer to display correctly and independently, it fails to synchronize with the MjModel m and data MjData d. On the other hand, threading achieves synchronization with the model and data, but the viewers interfere with each other, especially when I try to open a menu in a viewer.

MultiViewers.mp4

Minimal model and/or code that explain my question

import mujoco
import mujoco.viewer
import time
import multiprocessing
import threading

if __name__ == "__main__":
    XML=r"""
    <mujoco>
      <worldbody>
        <body pos="0 0 0">
          <freejoint/>
          <geom type="sphere" size=".1" rgba=".9 .9 .1 1"/>
        </body>
      </worldbody>
    </mujoco>
    """

    model_1 = mujoco.MjModel.from_xml_string(XML)
    data_1 = mujoco.MjData(model_1)
    mujoco.mj_step(model_1, data_1)

    model_2 = mujoco.MjModel.from_xml_string(XML)
    data_2 = mujoco.MjData(model_2)
    mujoco.mj_step(model_2, data_2)

    def render(model, data):
        with mujoco.viewer.launch_passive(model, data) as viewer:
            while viewer.is_running():
                viewer.sync()
                time.sleep(0.001)

    use_multiprocessing = True # Neither multiprocess or threading works
    if use_multiprocessing:
        thread1 = multiprocessing.Process(target=render, args=(model_1, data_1))
        thread2 = multiprocessing.Process(target=render, args=(model_2, data_2))
    else:
        thread1 = threading.Thread(target=render, args=(model_1, data_1))
        thread2 = threading.Thread(target=render, args=(model_2, data_2))
    thread1.start()
    thread2.start()
    for step in range(10000):
        print(step)
        mujoco.mj_step(model_1, data_1)
        mujoco.mj_step(model_2, data_2)
        time.sleep(0.001)

    thread1.join()
    thread2.join()

Confirmations

I searched the latest documentation thoroughly before posting.
I searched previous Issues and Discussions, I am certain this has not been raised before.

yuvaltassa · 2025-02-18T15:05:52Z

yuvaltassa
Feb 18, 2025
Maintainer

@vikashplus, I think you know how to do this?

4 replies

vikashplus Feb 18, 2025

I also tried doing something similar without success.

I vaguely remember the rationalization being related to the viewer needing the main thread (cc @saran-t). @HoangGiang93 - are you able to run even a single viewer on a separate thread?

HoangGiang93 Feb 18, 2025
Author

I can run viewer including mj_step separately only by using multiprocessing. But it's not what I want, I need the mj_step in the main thread.

vikashplus Feb 18, 2025

I'm curious if you are able to run rendering in a NON-main thread

with mujoco.viewer.launch_passive(model, data) as viewer:
            while viewer.is_running():
                viewer.sync()

HoangGiang93 Feb 19, 2025
Author

yes I could, as you can see in the video, the multiprocessing provides two independent viewer, but it seems the mj_step outside the Process doesn't share the same data, so I can render but can't interact with it programmatically.

v-r-a · 2025-02-18T19:48:45Z

v-r-a
Feb 18, 2025

If not seen already:
https://discourse.glfw.org/t/multithreading-with-glfw/812/2
https://discourse.glfw.org/t/multithreading-glfw/573 (answer by elmindreda)
(I'm too naive to conclude, but it looks like bypassing the main thread might create inconsistencies across different platforms.)

1 reply

HoangGiang93 Feb 19, 2025
Author

Thank you, I'm gonna need some coffee for this...

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How can I implement multiple viewers for different simulations? #2429

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HoangGiang93 Feb 16, 2025

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 2 comments · 5 replies

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yuvaltassa Feb 18, 2025 Maintainer

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vikashplus Feb 18, 2025

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HoangGiang93 Feb 18, 2025 Author

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v-r-a Feb 18, 2025

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HoangGiang93
Feb 16, 2025

Replies: 2 comments 5 replies

yuvaltassa
Feb 18, 2025
Maintainer

HoangGiang93 Feb 18, 2025
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HoangGiang93 Feb 19, 2025
Author

v-r-a
Feb 18, 2025

HoangGiang93 Feb 19, 2025
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