[viewer] Importing viewer module on macos immediately kills maplotlib windows

[ShravanTata]

On MacOS, importing the viewer module from dm_control immediately kills the matplotlib plot figures even when it should be ideally blocked with plt.show(). To reproduce the issue run the code below as a script:

import matplotlib
import matplotlib.pyplot as plt

from dm_control import viewer

if __name__ == '__main__':
    print(f"Matplotlib backed {matplotlib.get_backend()} ")
    plt.plot()
    plt.show(block=True)

NOTE : To reproduce the bug from the above script make sure that backend used by matplotlib (printed on the terminal) is MacOSX. When using other non default backends on MacOS the issue goes away.

Looking into it I found that the issue comes from https://github.com/deepmind/dm_control/blob/3c67a42d021b97808fcc075c0c468d78f0c2233f/dm_control/_render/glfw_renderer.py#L28 Seems like having glfw.init() run globally is the cause.

[saran-t]

Haven't had a chance to actually look into this yet, but regarding glfw.init(), that's the only way to run it. There isn't a "run it locally" option. If it is in fact glfw.init() that's causing the problem then it's likely an incompatibility between glfw and the particular matplotlib backend.

[ShravanTata]

Yes, it is definitely a problem particularly with the MacOSX backend which happens to be the default. When I switch to, for example Qt backend (to permanently do it add the following to your (bash)rc export MPLBACKEND=QtAgg) the issue goes away

[saran-t]

Are you getting any error message or does it just silently close?

[ShravanTata]

No errors/warnings are raised. It just silently closes