"RuntimeError: already started" after VSCode Update.

[mau21mau]

Environment data

• VS Code version: 1.46.1
• Extension version: v2020.6.89148
• OS and version: Mint 19.3 Cinamon
• Python version: Python3.6
• Type of virtual environment used: virtualenv + virtualenvwrapper
• Relevant/affected Python packages and their versions: XXX
• Relevant/affected Python-related VS Code extensions and their versions: XXX
• Jedi or Language Server? (i.e. what is "python.jediEnabled" set to; more info How to update the language server to the latest stable version #3977): XXX
• Value of the python.languageServer setting: XXX

I have been using VSCode to debug Python for almost a year now with the following run configuration from my launch.json file:

{
    "name": "Microservices",
    "type": "python",
    "request": "launch",
    "program": "/home/user/.virtualenvs/core-microservices/bin/gunicorn",
    "gevent": true,
    "args": [
        "main:app",
        "--bind=127.0.0.1:8080",
        "--worker-class",
        "eventlet",
        "-w",
        "4",
        "--timeout=7200"
    ],
    "envFile": "${workspaceFolder}/microservices.env",
    "postDebugTask": "killdebugger"
}

After the last update, when I try to run the debugger I get the following stack trace:

[2020-06-19 18:24:23 -0300] [18447] [INFO] Unhandled exception in main loop
Traceback (most recent call last):
  File "/home/mauricio/.virtualenvs/core-microservices/lib/python3.6/site-packages/gunicorn/arbiter.py", line 203, in run
    self.manage_workers()
  File "/home/mauricio/.virtualenvs/core-microservices/lib/python3.6/site-packages/gunicorn/arbiter.py", line 545, in manage_workers
    self.spawn_workers()
  File "/home/mauricio/.virtualenvs/core-microservices/lib/python3.6/site-packages/gunicorn/arbiter.py", line 616, in spawn_workers
    self.spawn_worker()
  File "/home/mauricio/.virtualenvs/core-microservices/lib/python3.6/site-packages/gunicorn/arbiter.py", line 567, in spawn_worker
    pid = os.fork()
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
    _on_forked_process()
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    pydevd.settrace_forked()
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    patch_multiprocessing=True,
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    wait_for_ready_to_run,
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
    debugger.connect(host, port)  # Note: connect can raise error.
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 1060, in connect
    s = start_client(host, port)
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 136, in _start_client
    return start_client(daemon, h, p)
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
    return f(*args, **kwargs)
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
    sock, start_session = daemon.start_client((host, port))
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
    with self.started():
  File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
    return next(self.gen)
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
    self.start()
  File "/home/mauricio/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
    raise RuntimeError('already started')

Steps to reproduce:

[NOTE: Self-contained, minimal reproducing code samples are extremely helpful and will expedite addressing your issue]

1. Just try to debug a python application with the latest version of the VScode editor and the Python Extension as well.

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

XXX

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help; turn on source maps to make any tracebacks be useful by running Enable source map support for extension debugging)

XXXX

[neverrop]

I have also encountered this problem, hope it can be fixed soon.

[garrickbrazil]

I also came across this error after an automatic update to the extension. I tried to downgrade the extension but gave up after a few tries.

My workaround is to turn off all multi-threading in my code... hope it gets fixed soon

[noymer]

They are my steps to reproduce:

my environment

version: 1.46.1 (user setup)
commit: cd9ea6488829f560dc949a8b2fb789f3cdc05f5d
date: 2020-06-17T21:13:20.174Z
Electron: 7.3.1
Chrome: 78.0.3904.130
Node.js: 12.8.1
V8: 7.8.279.23-electron.0
OS: Windows_NT x64 10.0.17763

I use remote WSL: Ubuntu-18.04
Python: 3.6.7 
ptvsd: 4.3.2

code

// try_multiprocess.py
from multiprocessing import Pool

def f(x):
    return x*x

if __name__ == '__main__':
    with Pool(5) as p:
        print(p.map(f, [1, 2, 3]))

launch.json

        {
            "name": "try multiprocess",
            "type": "python",
            "request": "launch",
            "program": "${workspaceFolder}/try_multiprocess.py",
            "console": "integratedTerminal",
            "justMyCode": false,
        }

error

run by debug and get errors as below

$ env PYTHONIOENCODING=UTF-8 PYTHONUNBUFFERED=1 /usr/bin/python3 /home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py --default --client --host localhost --port 53608 /home/noymer/program/sandbox/try_multiprocess.py 
E00000.214: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            

E00000.223: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            

E00000.232: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            

E00000.248: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            

E00000.259: Exception escaped from start_client
            
            Traceback (most recent call last):
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
                return f(*args, **kwargs)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
                sock, start_session = daemon.start_client((host, port))
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
                with self.started():
              File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
                return next(self.gen)
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
                self.start()
              File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
                raise RuntimeError('already started')
            RuntimeError: already started
            

Traceback (most recent call last):
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py", line 48, in <module>
    main(ptvsdArgs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 432, in main
    run()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 316, in run_file
    runpy.run_path(target, run_name='__main__')
  File "/usr/lib/python3.6/runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "/usr/lib/python3.6/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/noymer/program/sandbox/try_multiprocess.py", line 7, in <module>
    with Pool(5) as p:
  File "/usr/lib/python3.6/multiprocessing/context.py", line 119, in Pool
    context=self.get_context())
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 255, in _repopulate_pool_static
    w.start()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 105, in start
    self._popen = self._Popen(self)
  File "/usr/lib/python3.6/multiprocessing/context.py", line 277, in _Popen
    return Popen(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 66, in _launch
    self.pid = os.fork()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
    _on_forked_process()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    pydevd.settrace_forked()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    patch_multiprocessing=True,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    wait_for_ready_to_run,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
    debugger.connect(host, port)  # Note: connect can raise error.
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 1060, in connect
    s = start_client(host, port)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 136, in _start_client
    return start_client(daemon, h, p)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
    return f(*args, **kwargs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
    sock, start_session = daemon.start_client((host, port))
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
    with self.started():
  File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
    return next(self.gen)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
    self.start()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
    raise RuntimeError('already started')
RuntimeError: already started
Traceback (most recent call last):
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py", line 48, in <module>
    main(ptvsdArgs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 432, in main
    run()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 316, in run_file
    runpy.run_path(target, run_name='__main__')
  File "/usr/lib/python3.6/runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "/usr/lib/python3.6/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/noymer/program/sandbox/try_multiprocess.py", line 7, in <module>
    with Pool(5) as p:
  File "/usr/lib/python3.6/multiprocessing/context.py", line 119, in Pool
    context=self.get_context())
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 255, in _repopulate_pool_static
    w.start()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 105, in start
    self._popen = self._Popen(self)
  File "/usr/lib/python3.6/multiprocessing/context.py", line 277, in _Popen
    return Popen(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 66, in _launch
Traceback (most recent call last):
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py", line 48, in <module>
    self.pid = os.fork()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
    _on_forked_process()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    pydevd.settrace_forked()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    main(ptvsdArgs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 432, in main
    run()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 316, in run_file
    patch_multiprocessing=True,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    runpy.run_path(target, run_name='__main__')
  File "/usr/lib/python3.6/runpy.py", line 263, in run_path
    wait_for_ready_to_run,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
    pkg_name=pkg_name, script_name=fname)
  File "/usr/lib/python3.6/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/noymer/program/sandbox/try_multiprocess.py", line 7, in <module>
    debugger.connect(host, port)  # Note: connect can raise error.
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 1060, in connect
    with Pool(5) as p:
  File "/usr/lib/python3.6/multiprocessing/context.py", line 119, in Pool
    context=self.get_context())
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    s = start_client(host, port)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 136, in _start_client
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 255, in _repopulate_pool_static
    return start_client(daemon, h, p)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
    w.start()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 105, in start
Traceback (most recent call last):
    return f(*args, **kwargs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py", line 48, in <module>
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
    self._popen = self._Popen(self)
  File "/usr/lib/python3.6/multiprocessing/context.py", line 277, in _Popen
    sock, start_session = daemon.start_client((host, port))
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
    main(ptvsdArgs)
    return Popen(process_obj)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 432, in main
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 19, in __init__
    with self.started():
  File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
    run()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 316, in run_file
    self._launch(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 66, in _launch
    return next(self.gen)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
    self.pid = os.fork()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
    runpy.run_path(target, run_name='__main__')
    self.start()
  File "/usr/lib/python3.6/runpy.py", line 263, in run_path
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
    pkg_name=pkg_name, script_name=fname)
  File "/usr/lib/python3.6/runpy.py", line 96, in _run_module_code
    raise RuntimeError('already started')
RuntimeError: already started
    _on_forked_process()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    pydevd.settrace_forked()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    exec(code, run_globals)
  File "/home/noymer/program/sandbox/try_multiprocess.py", line 7, in <module>
    with Pool(5) as p:
  File "/usr/lib/python3.6/multiprocessing/context.py", line 119, in Pool
    context=self.get_context())
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 255, in _repopulate_pool_static
    patch_multiprocessing=True,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    w.start()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 105, in start
    wait_for_ready_to_run,
    self._popen = self._Popen(self)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
  File "/usr/lib/python3.6/multiprocessing/context.py", line 277, in _Popen
Error in atexit._run_exitfuncs:
    return Popen(process_obj)
Traceback (most recent call last):
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 19, in __init__
  File "/usr/lib/python3.6/multiprocessing/util.py", line 319, in _exit_function
    self._launch(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 66, in _launch
    p.join()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 122, in join
    self.pid = os.fork()
    assert self._parent_pid == os.getpid(), 'can only join a child process'
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
AssertionError: can only join a child process
    _on_forked_process()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    pydevd.settrace_forked()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    patch_multiprocessing=True,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    wait_for_ready_to_run,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
    debugger.connect(host, port)  # Note: connect can raise error.
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 1060, in connect
    s = start_client(host, port)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 136, in _start_client
    return start_client(daemon, h, p)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
    return f(*args, **kwargs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
    sock, start_session = daemon.start_client((host, port))
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
    with self.started():
  File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
    return next(self.gen)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
    self.start()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
    raise RuntimeError('already started')
RuntimeError: already started
Traceback (most recent call last):
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/ptvsd_launcher.py", line 48, in <module>
    main(ptvsdArgs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 432, in main
    run()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/__main__.py", line 316, in run_file
    runpy.run_path(target, run_name='__main__')
  File "/usr/lib/python3.6/runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "/usr/lib/python3.6/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/noymer/program/sandbox/try_multiprocess.py", line 7, in <module>
    with Pool(5) as p:
  File "/usr/lib/python3.6/multiprocessing/context.py", line 119, in Pool
    context=self.get_context())
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 175, in __init__
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/usr/lib/python3.6/multiprocessing/util.py", line 319, in _exit_function
    self._repopulate_pool()
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 236, in _repopulate_pool
    self._wrap_exception)
  File "/usr/lib/python3.6/multiprocessing/pool.py", line 255, in _repopulate_pool_static
    p.join()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 122, in join
    w.start()
    assert self._parent_pid == os.getpid(), 'can only join a child process'
  File "/usr/lib/python3.6/multiprocessing/process.py", line 105, in start
AssertionError: can only join a child process
    self._popen = self._Popen(self)
  File "/usr/lib/python3.6/multiprocessing/context.py", line 277, in _Popen
    return Popen(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/lib/python3.6/multiprocessing/popen_fork.py", line 66, in _launch
    self.pid = os.fork()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 528, in new_fork
    _on_forked_process()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/_pydev_bundle/pydev_monkey.py", line 50, in _on_forked_process
    pydevd.settrace_forked()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2427, in settrace_forked
    patch_multiprocessing=True,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2179, in settrace
    wait_for_ready_to_run,
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 2230, in _locked_settrace
    debugger.connect(host, port)  # Note: connect can raise error.
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/_vendored/pydevd/pydevd.py", line 1060, in connect
    s = start_client(host, port)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 136, in _start_client
    return start_client(daemon, h, p)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/log.py", line 110, in g
    return f(*args, **kwargs)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/pydevd_hooks.py", line 74, in start_client
    sock, start_session = daemon.start_client((host, port))
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 214, in start_client
    with self.started():
  File "/usr/lib/python3.6/contextlib.py", line 81, in __enter__
    return next(self.gen)
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 110, in started
    self.start()
  File "/home/noymer/.vscode-server/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/old_ptvsd/ptvsd/daemon.py", line 145, in start
    raise RuntimeError('already started')
RuntimeError: already started
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/usr/lib/python3.6/multiprocessing/util.py", line 319, in _exit_function
    p.join()
  File "/usr/lib/python3.6/multiprocessing/process.py", line 122, in join
    assert self._parent_pid == os.getpid(), 'can only join a child process'
AssertionError: can only join a child process
Terminated

[noymer]

Though I don't understand precisely, @int19h says as this link,
microsoft/ptvsd#2129 (comment)

And the recent commit changes around of optin and optout of DebugAdapterFactory, PtvsdWheels37
650e4a9

So this commit will be the cause.

[int19h]

This commit removes the experiment along with the old debugger, so it actually fixes this issue, in a sense. But it was only merged 3 days ago, so it's only present in insiders build, not in stable.

(Consequently, if you want a quick workaround - just install insiders!)

[int19h]

To work around without insiders build, please add the following to your settings.json:

    "python.experiments.optInto": [
        "DebugAdapterFactory - experiment",
        "PtvsdWheels37 - experiment"
    ],

To be clear, this is still a bug, and the above is a temporary workaround. We're investigating the root cause.

[int19h]

This should now be fixed. Can you please try restarting VSCode, and see if everything works for you now?

[noymer]

Thank you @int19h

At the same situation as #12481 (comment) , after restarting VSCode, the code is executed without the problem.

But after finishing the program, errors Server[6] disconnected unexpectedly Server[pid=5450] disconnected unexpectedly appear.
(It's after finishing the code, so I can use remote debugging)

[int19h]

Can you please file a separate issue at https://github.com/microsoft/debugpy ?

[noymer]

I have posted a issue
microsoft/debugpy#303

Thank you for your quick reply and fix @int19h !