It seems that render() works even inside thread.

[ravijo]

It seems that render() works even inside a thread. Just remember to get rid of the exception by removing the following lines:

nes-py/nes_py/_image_viewer.py

Lines 25 to 28 in b6f4e26

	import threading
	if threading.current_thread() is not threading.main_thread():
	msg = 'rendering from python threads is not supported'
	raise RuntimeError(msg)

A sample code is shown below:

import os
os.environ['OMP_NUM_THREADS'] = '1'

import threading
import gym_super_mario_bros
from gym_super_mario_bros.actions import SIMPLE_MOVEMENT
from nes_py.wrappers import JoypadSpace


def dummy_fun(steps):
    import numpy as np
    rng = np.random.default_rng(steps)
    sum = 0.0
    for _ in range(steps):
        rfloat = rng.random()
        sum += rfloat
    print(f'sum {sum}')


def do_something(steps):
    print('inside do_something')
    env = JoypadSpace(gym_super_mario_bros.make('SuperMarioBros-1-1-v0', new_step_api=False), SIMPLE_MOVEMENT)
    done = True
    for _ in range(steps):
        if done:
            state = env.reset()
        state, reward, done, info = env.step(env.action_space.sample())
        env.render()
    print(f'state shape {state.shape}')
    env.close()


def main():
    steps = 5000
    thread1 = threading.Thread(
        target=dummy_fun,
        args=(
            steps,
        ),
    )
    thread1.start()

    thread2 = threading.Thread(
        target=do_something,
        args=(
            steps,
        ),
    )
    thread2.start()

    thread1.join()
    thread2.join()


if __name__ == '__main__':
    main()

Below is the screenshot:

[ravijo]

I created a pull request. let me know if additional checking is required:
#92

[Kautenja]

Thanks for writing this up and for testing the threaded render path. After revisiting the rendering stack, the current project direction is to keep windowed human rendering on the main Python thread only, rather than removing the guard in the viewer path. The current code still enforces that behavior, and the updated documentation now spells it out explicitly: rgb_array rendering is supported from threads/processes, while windowed human rendering is intentionally limited to the owning process main thread. Since this area has now been clarified and the requested behavior is not something we plan to support in the maintained path, I’m closing this issue as not planned.