Debugging with shortly-lived subprocesses gives 'Server disconnected unexpectedly'

[bbartyzel]

VSCode shows an error when a subprocess in a program under debug exits very fast and the subProcess: true is defined in launch.json.

The problem disappears when subProcess: false is set.
Reproduced on two different machines (W11+WSL)

When running the debugger via Powershell on Windows the problem is not reproducible. Only W11+WSL.

Environment data

• debugpy version: v2025.8.0
• OS and version: Windows 11 + Debian GNU/Linux 12 (bookworm) (WSL2) [Remote host]
• Python version: 3.11.2
• Using VS Code: 1.101.0

Actual behavior

When debugging a python program that spawns a subprocess that exits too quickly this error is shown:

It happens randomly and is possibly related to the subprocess exiting while the debugger is being attached.

Expected behavior

Error does not pop up and the debugger handles such case gracefully.

Steps to reproduce:

1. Run code that spawns another python subprocess - for example with a module that doesn't exist

import subprocess

def main():
    cmd = "python3 -m idontexist"
    for i in range(0, 20):
        process = subprocess.Popen(cmd.split())
        process.wait()

if __name__ == "__main__":
    main()

[rchiodo]

Does the main process stay connected? I can't reproduce this myself

[bbartyzel]

Yes, the main process stays connected, I can go through another iteration of the for loop when the error shows. Maybe its connected to running the project from WSL? I will try to reproduce this on pure Windows.
I can reproduce it fairly easy on WSL.

[bbartyzel]

I can't reproduce the issue running the debugger via Powershell. When I open the project on WSL and start debugging the error shows right up.

Edit: tested in on a second machine, also W11+WSL - the same problem occurs.