Current logic to quit Game causes simharness vectorized environment setup to crash

[afennelly-mitre]

Summary

From the perspective of simharness, we need to be able to leverage environment vectorization, which is provided by rllib. The crux of the issue is as follows:

If one sub-environment calls pygame.quit(), then it messes with all other sub-environments in the same process who aren’t yet “ready” to quit, causing the program to crash. This happens primarily by setting the rendering property to False:

sim = FireSimulation(...)
sim.rendering = True

...

sim.rendering = False

The final line in the above pseudo code will call self._game.quit() (see this line in simulation.py).

Fix

To resolve this issue, we simply need to add a class variable to the simfire.game.Game class, something like num_active_games that can be incremented when a new Game object is initialized, and decremented when we call Game.quit(). When we try to quit, if num_active_games == 0, only then can we call pygame.quit() with confidence.