Subject: Re: [PATCH v3] lockfile: add PID file for debugging stale locks

From: Jeff King <[email-masked]>
Date: Sat, 27 Dec 2025 02:50:25 -0500

On Wed, Dec 24, 2025 at 12:24:13PM +0000, Paulo Casaretto via GitGitGadget wrote:

> For a lock file "foo.lock", the PID file is named "foo~pid.lock". The
> tilde character is forbidden in refnames and allowed in Windows
> filenames, which guarantees no collision with the refs namespace
> (e.g., refs "foo" and "foo~pid" cannot both exist). The file uses a
> simple key-value format ("pid <value>") following the same pattern as
> Git object headers, making it extensible for future metadata.

FWIW, I like this approach, as the earlier collision possibilities in
earlier iterations made me a bit uncomfortable.

But then I wondered...

> The feature is controlled via core.lockfilePid configuration, which
> accepts per-component values similar to core.fsync:
> 
>   - none: Disable for all components (default)
>   - all: Enable for all components
>   - index, config, refs, commit-graph, midx, shallow, gc, other:
>     Enable for specific components

Do we really need this complexity now? I can see reasons why a user
might want to switch the feature on (because they want the extra pid
debugging info) or off (because they do not want the extra filesystem
operations or potential cleanup hassle of extra stale files).

But if the collision problems in the ref namespace are now solved, does
anybody really care about turning it on just for particular subsystems?
I'd think they would want all or nothing.

Trying to devil's advocate myself: maybe somebody is concerned about
filesystem overhead for frequently-written files like refs but not for
others, like config? That feels unlikely to me, but at least possible.

But if we were to ditch the subsystem-granularity for config, then all
of the extra LOCKFILE_* arguments here could just go away.

-Peff