…iteCommitGraph

The git fetch command recently learned to extend the --jobs=<n> option to
cover the --multiple mode: it will run multiple fetches in parallel.

Together with the recent support to write commit-graphs automatically after
each fetch by setting fetch.writeCommitGraph, this led to frequent issues
where the commit-graph-chain.lock file could not be created because a
parallel job had already created it.

This pair of patches first introduces the command-line option
--write-commit-graph (together with the --no-* variant) and then uses it to
avoid writing the commit-graph until all fetch jobs are complete.

I don't think that we will want to rush this into Git v2.24.0 because that
release is imminent, and this is quite a corner case that I am fixing here.
It's more of a FYI that I send this before v2.24.0 is available.

Johannes Schindelin (2):
  fetch: add the command-line option `--write-commit-graph`
  fetch: avoid locking issues between fetch.jobs/fetch.writeCommitGraph

 Documentation/fetch-options.txt |  4 ++++
 builtin/fetch.c                 | 10 ++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

base-commit: efd54442381a2792186abc994060b8f7dd8b834b

Submitted-As: https://public-inbox.org/git/pull.443.git.1572740518.gitgitgadget@gmail.com