RuntimeError already started

Env:

os: Ubuntu
python3
pytorch
vscode

Desc

在上述环境中运行A3C多进程模型，使用命令行时没问题，使用vscode时出现 'RuntimeError: already started' 的错误，具体错误信息如下：

E00000.755: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/haikuoxin/.vscode/extensions/ms-python.python-2019.11.50794/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/haikuoxin/.vscode/extensions/ms-python.python-2019.11.50794/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/haikuoxin/.vscode/extensions/ms-python.python-2019.11.50794/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/home/haikuoxin/anaconda3/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/haikuoxin/.vscode/extensions/ms-python.python-2019.11.50794/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/haikuoxin/.vscode/extensions/ms-python.python-2019.11.50794/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            
Traceback (most recent call last):

Error in atexit._run_exitfuncs:
Error in atexit._run_exitfuncs:
Traceback (most recent call last):

Solution

在自己的代码头添加以下代码行：

import torch.multiprocessing as mp
mp.set_start_method('spawn', True)