[GSoC][RFC] New approach: improve threading at git-grep

[GSoC][RFC] New approach: improve threading at git-grep

[Matheus Tavares Bernardino]

Hi, everyone

I've been working on making the pack access code thread safe, as my
GSoC project[1]. I was working directly at sha1-file.c global states
targeting, in the far distance, to parallelize git-blame. But my
mentors and I decided to take a different path, as a better way to
continuous validate the work being done and be able to see small
continuous improvements: the idea is to focus on the object store call
chains originated at git-grep. Making them thread-safe, we should be
able to re-enable threading when greping blobs[2] and go refining
git-grep's locks along the way, for a better performance.

I just posted about the overall idea together with some analysis I've
made on git-grep, here:
https://matheustavares.gitlab.io/posts/week-4-a-different-approach
Please, let me know if you have any comments or suggestions.

Thanks,
Matheus

[1]: https://matheustavares.gitlab.io/assets/Matheus_Tavares_GSoC_Proposal.pdf
[2]: Disabled by 53b8d93 (“grep: disable threading in non-worktree
case”, 2011-12-12), because it was causing slowdowns