SUMO can Freeze When Reloading

[Gamenot]

BUG REPORT

I have confirmed, SUMO can freeze when reloading too many times.

SMARTS Version
0.4.12

Previous associated issues
#465 (comment)

Steps to reproduce the bug
Run the following code:

import os

import gym
from smarts.core.agent_interface import AgentInterface, AgentType
from smarts.core.agent import AgentSpec, Agent
import numpy as np


class SimpleAgent(Agent):
    def __init__(self):
        self.action_space = gym.spaces.Box(
            low=np.array([0, 0, -1.0]), high=np.array([1.0, 1.0, 1.0]), dtype=np.float32
        )

    def act(self, obs):
        # return "keep_lane"
        return self.action_space.sample()


agent_spec = AgentSpec(
    interface=AgentInterface.from_type(AgentType.Full, max_episode_steps=None),
    agent_builder=SimpleAgent,
)

agent_specs = {
    "Agent-001": agent_spec,
    # "Agent-008": agent_spec,
}

env = gym.make(
    "smarts.env:hiway-v0",
    scenarios=["scenarios/loop"],
    agent_specs=agent_specs,
)

agents = {
    agent_id: agent_spec.build_agent()
    for agent_id, agent_spec in agent_specs.items()
}
observations = env.reset()

for i in range(100000000):
    print(i)
    agent_actions = {
        agent_id: agents[agent_id].act(agent_obs)
        for agent_id, agent_obs in observations.items()
    }
    for agent_id, agent_obs in observations.items():
        a = agents[agent_id].act(agent_obs)
    observations, r, d, i = env.step(agent_actions)
    observations = env.reset()

Resulting and expected behaviour
Expect to get 100000000 resets but SUMO crashes before then.

Error logs and screenshots

pybullet build time: Dec 23 2020 01:47:29
32427
pybullet build time: Dec 23 2020 01:47:29
32428
pybullet build time: Dec 23 2020 01:47:29
32429
Traceback (most recent call last):
 File "examples/simple_example_test.py", line 55, in <module>
   observations = env.reset()
 File "/home/dev/Desktop/repos/NewSMARTS/SMARTS/smarts/env/hiway_env.py", line 188, in reset
   env_observations = self._smarts.reset(scenario)
 File "/home/dev/Desktop/repos/NewSMARTS/SMARTS/smarts/core/smarts.py", line 314, in reset
   self.setup(scenario)
 File "/home/dev/Desktop/repos/NewSMARTS/SMARTS/smarts/core/smarts.py", line 361, in setup
   provider_state = self._setup_providers(self._scenario)
 File "/home/dev/Desktop/repos/NewSMARTS/SMARTS/smarts/core/smarts.py", line 656, in _setup_providers
   provider_state.merge(provider.setup(scenario))
 File "/home/dev/Desktop/repos/NewSMARTS/SMARTS/smarts/core/sumo_traffic_simulation.py", line 247, in setup
   self._traci_conn.simulation.subscribe(
 File "/usr/share/sumo/tools/traci/_simulation.py", line 468, in subscribe
   Domain.subscribe(self, "", varIDs, begin, end)
 File "/usr/share/sumo/tools/traci/domain.py", line 209, in subscribe
   self._connection._subscribe(self._subscribeID, begin, end, objectID, varIDs, parameters)
 File "/usr/share/sumo/tools/traci/connection.py", line 242, in _subscribe
   result = self._sendCmd(cmdID, (begin, end), objID, format, *args)
 File "/usr/share/sumo/tools/traci/connection.py", line 180, in _sendCmd
   return self._sendExact()
 File "/usr/share/sumo/tools/traci/connection.py", line 90, in _sendExact
   raise FatalTraCIError("connection closed by SUMO")
traci.exceptions.FatalTraCIError: connection closed by SUMO

My device also ended with a surprising error:

System information

• Operating system & Environment [Please note if using Docker]:
  • Ubuntu 18.04
• Number of system cores available
  • 16
• Python version [Please note if using Jupyter]
  • Python 3.7
• Python packages [e.g. from pip freeze]
  • pip_freeze.txt
• SUMO version
  • Eclipse SUMO sumo Version 1.8.0
• Date when bug occurred
  • 2020_01_26

Impact [If known]
Reloading a single scenario repeatedly may crash SUMO.

[Gamenot]

Addressed in #852