Fix zombie process accumulation from git operations in cloud environments

[nsingl00]

Problem

Fixes #975 and #1418

Git commands spawn helper processes (git-credential-helper, git-remote-https, ssh, git-upload-pack, git-receive-pack) that can become zombie processes when the main git process exits before its children complete. This is particularly
problematic in cloud/container environments where:

• The application runs as PID 1 or under minimal init systems
• Standard init process zombie reaping may be unreliable or slow
• Resource constraints can cause zombie accumulation over time

Root Cause

In containerized environments, our Jupyter application often becomes PID 1 due to exec usage in startup scripts, making it responsible for zombie process cleanup. Unlike robust init systems (systemd, launchd) found in local environments,
minimal container init systems may not reliably reap orphaned git helper processes.

Solution

Added a SIGCHLD signal handler that automatically reaps zombie processes system-wide. The handler:

• Uses non-blocking waitpid(-1, os.WNOHANG) to reap any zombie children
• Runs whenever any child process terminates (SIGCHLD signal)
• Prevents zombie accumulation without affecting normal git operations
• Logs reaped processes at debug level for monitoring

Testing

• Verified zombie processes are eliminated in cloud environments
• Confirmed normal git operations continue to work correctly
• No performance impact on git command execution

[github-actions]

👈 Launch a Binder on branch nsingl00/jupyterlab-git/subprocess

[nsingl00]

Hey @krassowski can you help review the PR?

[ellisonbg]

Thanks for working on this @nsingl00 - wonder if this is related to #975

[nsingl00]

Thanks for working on this @nsingl00 - wonder if this is related to #975

yes, it is related. The problem is , when in enterprise we run jupyter in a container environment where process ID 1 is not signal handler processes like tini, zombie process cleanup doesn't happen. Adding an extra SIGHandler to reap off the child processes in those scenarios would work. Added the PR for those cases.