New process started before current process has finished its bootstrapping

Describe the bug

There is a race condition in the multi-processing lib if you don't use

if __name__ == "__main__":
    main()

System Info

OS: Windows 10 Installed: via pip GPU: 970 Python: 3.6.5

Additional context

C:\Users\Ian\clones\rl-baselines-zoo>python enjoy.py --algo ppo2 --env Walker2DBulletEnv-v0 pybullet build time: Jan 11 2019 15:30:44 c:\users\ian\clones\gym\gym\logger.py:30: UserWarning: [33mWARN: gym.spaces.Box autodetected dtype as <class 'numpy.float32'>. Please provide explicit dtype.[0m warnings.warn(colorize('%s: %s'%('WARN', msg % args), 'yellow')) pybullet build time: Jan 11 2019 15:30:44 c:\users\ian\clones\gym\gym\logger.py:30: UserWarning: [33mWARN: gym.spaces.Box autodetected dtype as <class 'numpy.float32'>. Please provide explicit dtype.[0m warnings.warn(colorize('%s: %s'%('WARN', msg % args), 'yellow')) Traceback (most recent call last): File "", line 1, in File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_main exitcode = _main(fd) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 114, in _main prepare(preparation_data) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 225, in prepare _fixup_main_from_path(data['init_main_from_path']) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path run_name="mp_main__") File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 263, in run_path pkg_name=pkg_name, script_name=fname) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 96, in _run_module_code mod_name, mod_spec, pkg_name, script_name) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 85, in _run_code exec(code, run_globals) File "C:\Users\Ian\clones\rl-baselines-zoo\enjoy.py", line 59, in seed=args.seed, log_dir=log_dir, should_render=not args.no_render) File "C:\Users\Ian\clones\rl-baselines-zoo\utils\utils.py", line 115, in create_test_env env = SubprocVecEnv([make_env(env_id, 0, seed, log_dir)]) File "c:\users\ian\clones\stable-baselines\stable_baselines\common\vec_env\subproc_vec_env.py", line 59, in init process.start() File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\process.py", line 105, in start self._popen = self._Popen(self) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 223, in _Popen return _default_context.get_context().Process._Popen(process_obj) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 322, in _Popen return Popen(process_obj) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\popen_spawn_win32.py", line 33, in init__ prep_data = spawn.get_preparation_data(process_obj._name) File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 143, in get_preparation_data _check_not_importing_main() File "C:\Users\Ian\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 136, in _check_not_importing_main is not going to be frozen to produce an executable.''') RuntimeError: An attempt has been made to start a new process before the current process has finished its bootstrapping phase.

    This probably means that you are not using fork to start your
    child processes and you have forgotten to use the proper idiom
    in the main module:

        if __name__ == '__main__':
            freeze_support()
            ...

    The "freeze_support()" line can be omitted if the program
    is not going to be frozen to produce an executable.

araffin / rl-baselines-zoo

New process started before current process has finished its bootstrapping #8