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I am trying using Webots in combination with stable-baselines3 for reeinforcment-learning purpose. I tried using Webot with multiple instances, but connecting the controller to a specific one doesn't work. It mostly connects to the newest one. I wrote a runtime.ini giving the WEBOT_PID manually looking like

[environment variables]
WEBOTS_PID=1492

and even tried setting the environment variable in my Python code like

os.environ["WEBOTS_PID"] = str(1492)
self.simulation = WebotsInterface()

it doesn't connect to desired Instance.

Hotsch
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1 Answers1

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The WEBOTS_PID environment variable should be set before you start the robot controller, otherwise it is not taken into account. So, you cannot set it in the runtime.ini (which is anyhow ignored when launching extern controllers) nor in the controller itself. I would recommend you to write a script that sets the WEBOTS_PID first and then starts the controller program as an extern controller.

Olivier Michel
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    Thank you, I do now know how it works since I went additionally through the source code. For my usecase a workaround using mutex to connect a threads controller to the newest instance was sufficient. – Hotsch Sep 10 '21 at 10:25