VS Code Debugger Freezes When Using wrap_wsgi_app with debugpy

[mrbaguettefr]

Environment data

• debugpy version: XXX (run import debugpy; print(debugpy.__version__) if uncertain) 1.8.13
• OS and version:
• Python version (& distribution if applicable, e.g. Anaconda):

Virtualenv
Python:         3.13.4
Implementation: CPython
Platform:   linux
OS:         posix
Python:     3.13.4
Path:       /home/tony/.pyenv/versions/3.13.4
Executable: /home/tony/.pyenv/versions/3.13.4/bin/python3.13

• Using VS Code

Actual behavior

• VS Code debugger gets stuck once breakpoint is hit.
• UI does not switch to source code line.
• Debugger controls (Resume, Step Out, etc.) are unresponsive.
• HTTP server hangs (no response).
• However, the VS Code CALL STACK shows status: "PAUSED".

Expected behavior

• Debugger pauses on the specified line and focuses editor on source code.
• Debugger controls should remain fully functional.
• Upon resuming, the HTTP server should respond correctly:

HTTP/1.0 200 OK
Content-Length: 13
Content-Type: text/plain
Date: Wed, 11 Jun 2025 20:54:32 GMT
Server: WSGIServer/0.2 CPython/3.13.4

Hello world!

Steps to reproduce:

1. Clone the sample project: https://github.com/totobest/python-debug-test
2. Setup Python interpreter and install venv (poetry configuration is included)
3. Launch the included "wsgiref" debug configuration..
4. Set a breakpoint on line 5 or 6 of main.py..
5. In a terminal, run: curl -i localhost:8000

Additional Context

• Issue occurs consistently across Python versions 3.9 to 3.13.
• Tested across multiple Python Debugger extension versions (2024.x to latest).
• Works as expected when no breakpoint is set.
• Removing the call to wrap_wsgi_app(app) (line 8) resolves the issue entirely.

[mrbaguettefr]

Stacktrace when hitting CTRL+C and waiting a bit for the program to respond (using python3.12):

^CTraceback (most recent call last):
  File "/usr/lib/python3.12/runpy.py", line 198, in _run_module_as_main
    return _run_code(code, main_globals, None,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/runpy.py", line 88, in _run_code
    exec(code, run_globals)
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/adapter/../../debugpy/launcher/../../debugpy/__main__.py", line 71, in <module>
    cli.main()
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/adapter/../../debugpy/launcher/../../debugpy/../debugpy/server/cli.py", line 501, in main
    run()
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/adapter/../../debugpy/launcher/../../debugpy/../debugpy/server/cli.py", line 351, in run_file
    runpy.run_path(target, run_name="__main__")
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 310, in run_path
    return _run_module_code(code, init_globals, run_name, pkg_name=pkg_name, script_name=fname)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 127, in _run_module_code
    _run_code(code, mod_globals, init_globals, mod_name, mod_spec, pkg_name, script_name)
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 118, in _run_code
    exec(code, run_globals)
  File "main.py", line 10, in <module>
    with make_server('', 8000, app) as httpd:
  File "<stringsource>", line 69, in cfunc.to_py.__Pyx_CFunc_b0409f__29_pydevd_sys_monitoring_cython_object__lParen__etc_to_py_4code_4line.wrap
  File "_pydevd_sys_monitoring\\_pydevd_sys_monitoring_cython.pyx", line 1470, in _pydevd_sys_monitoring_cython._line_event
  File "_pydevd_sys_monitoring\\_pydevd_sys_monitoring_cython.pyx", line 1528, in _pydevd_sys_monitoring_cython._internal_line_event
  File "_pydevd_sys_monitoring\\_pydevd_sys_monitoring_cython.pyx", line 1950, in _pydevd_sys_monitoring_cython._do_wait_suspend
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/_vendored/pydevd/pydevd.py", line 2188, in do_wait_suspend
    keep_suspended = self._do_wait_suspend(thread, frame, event, arg, trace_suspend_type, from_this_thread, frames_tracker)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tony/.vscode-server/extensions/ms-python.debugpy-2025.8.0-linux-x64/bundled/libs/debugpy/_vendored/pydevd/pydevd.py", line 2257, in _do_wait_suspend
    notify_event.wait(wait_timeout)
  File "/usr/lib/python3.12/threading.py", line 655, in wait
    signaled = self._cond.wait(timeout)
               ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/threading.py", line 359, in wait
    gotit = waiter.acquire(True, timeout)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyboardInterrupt

[rchiodo]

I would hazard a guess that whatever wrap_wsgi_app is doing is interfering with the gui hooking in debugpy. So the suspend code is not running the 'gui' thread and it looks like the app is hung.

You could try forcing gui_in_use to true, although that might also require a new input hook.

debugpy/src/debugpy/_vendored/pydevd/pydevd.py

Line 697 in 99b202e

self.gui_in_use = False

[mrbaguettefr]

I changed the line to self.gui_in_use = True but same issue.
I'm not sure how do the input hooks work. I've seen there are many of them already:

The code of the wrap_wsgi_app function is here:
https://github.com/GoogleCloudPlatform/appengine-python-standard/blob/2764350f99a4c51c6227df74e02281b3640c453a/src/google/appengine/api/__init__.py#L46
I looked at it but I don't understand how does it work and where it could mess up with debugpy.

I created a bug report for the google team at the same time: GoogleCloudPlatform/appengine-python-standard#136.
Hopefully someone can help here as well.