Openai gym `render(mode='rgb_array')` crashes when executed within `multiprocessing.Process`

minimal.py

import gym
from multiprocessing import Process


class Worker(Process):
    def __init__(self, env_name, name=None, render_rgb=False):
        Process.__init__(self, name=name)
        self.env = gym.make(env_name)
        self.env.reset()
        self.render_rgb = render_rgb
        print('Environment initialized. {}'.format(self.name))

    def run(self, render_rgb=False):
        for _ in range(100):
            action = self.env.action_space.sample()
            obs, reward, done, _ = self.env.step(action)
            print(obs)
            if self.render_rgb:
                observation = self.env.render(mode='rgb_array')
            if done:
                print('Done with an epsidode for {}'.format(self.name))
                self.env.reset()


class Agent(object):

    def __init__(self, env_name, num_env, render_rgb=False):
        assert num_env > 0, 'Number of environments must be postive.'
        self.num_env = num_env
        self.workers = []

        for env_idx in range(num_env):
            env_worker = Worker(env_name, name=str(env_idx),
                                   render_rgb=render_rgb)
            self.workers.append(env_worker)

        for w in self.workers:
            w.start()

        for w in self.workers:
            w.join()


print('Initialization without render')
p_env = Agent('MountainCar-v0', 4, render_rgb=False)

print('Initialization with render')
p_env = Agent('MountainCar-v0', 4, render_rgb=True)