"RuntimeError: already started" after VSCode Update.

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 #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

[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]

Looks like everybody received the fix, so I’m going to go ahead and close this.