df67d73ca3
Concurrent config writers race for the ".lock" file, which is taken
with open(O_EXCL) and no retry, so the losers fail right away with
"could not lock config file".
This shows up with parallel "git worktree add -b" against the same
repository: each one writes a couple of branch.* keys and the losers
fail at random. Worse, "git worktree add" doesn't propagate that
failure to its exit code, so the tracking config is silently dropped.
(The swallowed error is a separate bug.)
Retry instead of giving up on the first EEXIST. The lock is only held
while rewriting a small file, so the loser only has to wait out the
other writers. Same approach as 4ff0f01cb7 (refs: retry acquiring
reference locks for 100ms, 2017-08-21).
On the semantics: the on-disk config is read only after the lock is
taken, so writers touching different keys can't lose each other's
change. Writers touching the same key still get last-writer-wins, but
that is already the case today and would need a compare-and-swap config
API to fix. The retry only turns hard failures into successes.
Default to 1000ms, like core.packedRefsTimeout: same shape of problem,
one shared file everyone serializes through. A larger timeout only
costs anything when a stale lock is left behind by a crash, which is
rare; a smaller one fails spuriously on slow filesystems (NTFS has
been seen needing more than 100ms). Make it configurable as
core.configLockTimeout. There is no chicken-and-egg problem: we read
the config before we lock it.
microsoft/git carries a similar patch (core.configWriteLockTimeoutMS,
default off) for Scalar's tests. Defaulting to non-zero here because
the worktree case fails silently.
Helped-by: Patrick Steinhardt <ps@pks.im>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Jörg Thalheim <joerg@thalheim.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.adoc to get started, then see
Documentation/giteveryday.adoc for a useful minimum set of commands, and
Documentation/git-<commandname>.adoc for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.adoc
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email to git+subscribe@vger.kernel.org (see https://subspace.kernel.org/subscribing.html for details). The mailing list archives are available at https://lore.kernel.org/git/, https://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks