`uv run` not running to completion

[amotl]

Summary

Hi. uv 0.6.12 user here. We wanted to report a problem that trips us when trying to invoke uv run from a Python process, in this case using the mcp library, where the program does not terminate (i.e. stalls), while invoking the same program using python works well.

We added a gist including the reproducer program uv_run_stuck_mcp.py, which you can use to replicate the flaw when invoking it like this:

python uv_run_stuck_mcp.py --uv

We've identified those issues to be possibly related to this problem, but we are not sure about it.

• Consider execv for uv run on Unix #3095
• Improve SIGINT handling in uv run #11009
• Handling of signal exit from subprocess is incorrect #11886
• "uv tool run" swallows SIGINT without forwarding to the underlying process #12108

Platform

macOS

Version

uv 0.6.12 (Homebrew 2025-04-02)

Python version

Python 3.13.2

[zanieb]

Thanks for the reproduction and issue links. Do you think you could minimize the reproduction further? I don't think I'll be able to debug it easily as-is.

[amotl]

Hi Zanie. I absolutely hear you that it's not a good reproducer, but I am currently not able to come up with a trimmed-down version. It must be revolving around "doing something with Python asyncio plus starting a process in the background", like MCP servers are doing it, or something like this.