Hi,
Most of the credit for this series should go to Stefan Beller. I just
decided to pull the trigger on sending out what we have so far.
This series is about API. It makes no functional change yet.
Today, when a git command wants to operate on some objects from another
repository (e.g., a submodule), it has two choices:
A. Use run_command to operate on that repository in a separate process.
B. Use add_to_alternates_memory to pretend the repository is an
alternate. This has a number of downsides. Aside from aesthetics,
one particularly painful consequence is that as alternates
accumulate, the number of packs git has to check for objects
increases, which can cause significant slowdowns.
Brandon Williams's recent work to introduce "struct repository" points
to a better way. Encapsulating object access in struct repository
would mean:
i. The API for accessing objects in another repository becomes more
simple and familiar (instead of using the CLI or abusing alternates).
ii. Operations on one repository do not interfere with another,
neither in semantics (e.g. replace objects do not work correctly
with the approach (B) above) nor performance (already described
above).
iii. Resources associated with access to a repository could be freed
when done with that repo.
iv. Thread-safe multiple readers to a single repository also become
straightforward, by using multiple repository objects for the same
repo.
This series is a small step in that direction.
At the end of this series, sha1_loose_object_info takes a repository
argument and can be independently called for multiple repositories.
Not incredibly useful on its own, but a future series will do the same
for sha1_object_info, which will be enough to migrate a caller in
submodule.c (which uses the object store for commit existence checks).
This series has a few phases:
1. Patch 1 is a cleanup that made some of the later patches easier.
2. Patches 2-6 create a struct object_store field inside struct
repository and move some globals to it.
3. Patches 7-24 are mechanical changes that update some functions to
accept a repository argument. The only goal is to make the later
patches that teach these functions to actual handle a repository
other than the_repository easier to review. The patches enforce
at compile time that no caller passes a repository other than
the_repository --- see patch 7 in particular for details on how
that works.
4. Patches 25-39 update the implementations of those functions to
handle a repository other than the_repository. This means the
safety check introduced in phase 3 goes away completely --- all
functions that gained a repository argument are safe to use with
a repository argument other than the_repository.
Patches 2-6 and 25-39 should be the most interesting to review. I'd
particularly appreciate if people can look over 25-39 carefully. We
were careful not to leave any calls to functions that assume they are
operating on the_repository, but a triple-check is always welcome.
Thanks as well to brian m. carlson, who showed us how such a long and
potentially tedius series can be made bearable for reviewers.
Thoughts of all kinds welcome, as always.
Thanks,
Jonathan Nieder (24):
pack: make packed_git_mru global a value instead of a pointer
object-store: move packed_git and packed_git_mru to object store
struct
pack: move prepare_packed_git_run_once to object store struct
pack: move approximate object count to object store struct
pack: add repository argument to install_packed_git
pack: add repository argument to prepare_packed_git_one
pack: add repository argument to rearrange_packed_git
pack: add repository argument to prepare_packed_git_mru
pack: add repository argument to prepare_packed_git
pack: add repository argument to reprepare_packed_git
pack: add repository argument to sha1_file_name
pack: add repository argument to map_sha1_file
pack: allow install_packed_git to handle arbitrary repositories
pack: allow rearrange_packed_git to handle arbitrary repositories
pack: allow prepare_packed_git_mru to handle arbitrary repositories
pack: allow prepare_packed_git_one to handle arbitrary repositories
pack: allow prepare_packed_git to handle arbitrary repositories
pack: allow reprepare_packed_git to handle arbitrary repositories
pack: allow sha1_file_name to handle arbitrary repositories
pack: allow stat_sha1_file to handle arbitrary repositories
pack: allow open_sha1_file to handle arbitrary repositories
pack: allow map_sha1_file_1 to handle arbitrary repositories
pack: allow map_sha1_file to handle arbitrary repositories
pack: allow sha1_loose_object_info to handle arbitrary repositories
Stefan Beller (15):
repository: introduce object store field
object-store: move alt_odb_list and alt_odb_tail to object store
struct
sha1_file: add repository argument to alt_odb_usable
sha1_file: add repository argument to link_alt_odb_entry
sha1_file: add repository argument to read_info_alternates
sha1_file: add repository argument to link_alt_odb_entries
sha1_file: add repository argument to stat_sha1_file
sha1_file: add repository argument to open_sha1_file
sha1_file: add repository argument to map_sha1_file_1
sha1_file: add repository argument to sha1_loose_object_info
object-store: add repository argument to prepare_alt_odb
object-store: add repository argument to foreach_alt_odb
sha1_file: allow alt_odb_usable to handle arbitrary repositories
object-store: allow prepare_alt_odb to handle arbitrary repositories
object-store: allow foreach_alt_odb to handle arbitrary repositories
builtin/count-objects.c | 10 ++-
builtin/fsck.c | 15 ++--
builtin/gc.c | 8 +-
builtin/index-pack.c | 1 +
builtin/pack-objects.c | 23 +++--
builtin/pack-redundant.c | 8 +-
builtin/receive-pack.c | 4 +-
builtin/submodule--helper.c | 4 +-
bulk-checkin.c | 3 +-
cache.h | 50 ++---------
contrib/coccinelle/packed_git.cocci | 15 ++++
fast-import.c | 10 ++-
fetch-pack.c | 3 +-
http-backend.c | 8 +-
http-push.c | 1 +
http-walker.c | 4 +-
http.c | 9 +-
mru.h | 1 +
object-store.h | 71 ++++++++++++++++
pack-bitmap.c | 6 +-
pack-check.c | 1 +
pack-revindex.c | 1 +
packfile.c | 94 ++++++++++----------
packfile.h | 6 +-
reachable.c | 1 +
repository.c | 4 +-
repository.h | 7 ++
server-info.c | 8 +-
sha1_file.c | 165 ++++++++++++++++++++----------------
sha1_name.c | 11 ++-
streaming.c | 5 +-
transport.c | 4 +-
32 files changed, 344 insertions(+), 217 deletions(-)
create mode 100644 contrib/coccinelle/packed_git.cocci
create mode 100644 object-store.h
--
2.14.1.581.gf28d330327
