gix-filter: long-running process filters are never waited for (274 zombies in 10.5 h)

[Tomasz Górka (tgorka)]

Hi! I ran into a process leak in gix-filter and have a small fix. I want to confirm before opening a PR.

driver::State::shutdown() is the only code that wait()s a long-running process filter, and nothing in the workspace calls it. Closing a child’s pipes makes it exit but doesn’t reap it, so on Unix every filter gitoxide launches keeps a process-table slot until the process exits. Clone for State resets running, so each per-thread clone in gix-status and in checkout abandons its own children.

What it looks like in practice, in a desktop app with filter.lfs.process registered: 274 zombies after 10.5 h against a kern.maxprocperuid of 2666, until nothing on the machine can fork() anymore. Also reproduced on Linux, where the child sits at state=Z in /proc.

The fix is ~30 lines of source: a &mut self form of shutdown that the by-value one delegates to, plus impl Drop for State. Non-breaking, and it covers status, checkout, diff, merge and worktree_stream at once. Details, evidence and tests are in two PRs on my fork — tests first, so the first one demonstrates the leak and the second flips it:

• full diff: main...tgorka:gitoxide:fix/reap-process-filter-children
• 1/2, the tests: feat(gix-filter): add process::Client::id() and pin the process filter child lifecycle tgorka/gitoxide#1
• 2/2, the fix: fix(gix-filter): reap process filter children instead of orphaning them tgorka/gitoxide#2

Two questions before I open it here:

1. Is a Drop that blocks in wait() acceptable? The child’s stdin is closed first, which is what tells it to exit, so it returns promptly — but I’d understand a preference for an opt-out instead.
2. Should Clone for State keep resetting running, or would you rather see one shared child pool? The current semantics are what multiply the leak.

Happy to reshape this however suits you, or to drop it if you’d rather take a different route.

[Sebastian Thiel (Byron)]

Thanks!

Created an issue from it #2947