"Why would one want to run it in parallel?" I hear you ask. I am glad you are curious, because a curious story is what it is, indeed. The `GIT-VERSION-GEN` script is quite a pillar of Git's source code, with most lines being unchanged for the past 15 years. Until the v2.48.0 release candidate cycle. Its original purpose was to generate the version string and store it in the `GIT-VERSION-FILE`. This paradigm changed quite dramatically when support for building with Meson was introduced. Most crucially, a38edab7c88b (Makefile: generate doc versions via GIT-VERSION-GEN, 2024-12-06) changed the way the documentation is built by using the `GIT-VERSION-GEN` file to write out the `asciidocor-extensions.rb` and `asciidoc.conf` files with now hard-coded version strings. Crucially, the Makefile rule to generate those files need to be run in every build because `GIT_VERSION` could have been specified, which would require these files to be changed. This introduced a surprising race condition! And this is how that race surfaces: When calling `make -j2 html man` from the top-level directory (a variant of which is invoked in Git for Windows' release process), two sub-processes are spawned, a `make -C Documentation html` one and a `make -C Documentation man` one. Both run the rule to (re-)generate `asciidoctor-extensions.rb` or `asciidoc.conf`, invoking `GIT-VERSION-GEN` to do so. That script first generates a temporary file (appending the `+` character to the filename), then looks whether it contains something different than the already existing file (if it exists, that is), and either replaces it if needed, or removes the temporary file. If one of the two parallel invocations removes that temporary file before the other can compare it, or even worse: if one tries to replace the target file just after the other _started_ writing the temporary file (but did not finish), that race condition now causes bad builds. This may sound highly theoretical, but due to Git's choices, Git for Windows is forced to use a (slow) POSIX emulation layer to run that script and in the blink of an eye it becomes very much not theoretical at all. See these failed GitHub workflow runs as Exhibit A: https://github.com/git-for-windows/git-sdk-32/actions/runs/12663456654 https://github.com/git-for-windows/git-sdk-32/actions/runs/12683174970 https://github.com/git-for-windows/git-sdk-64/actions/runs/12649348496 While it is undesirable to run this script over and over again, certainly when this involves above-mentioned slow POSIX emulation layer, the stage of the release cycle in which we are presently finding ourselves dictates that a quick and reliable work-around be implemented that works around the race condition without changing the overall architecture of the build process. This patch does that: By using a filename suffix for the temporary file that includes the currently-executing script's process ID, We guarantee that the two competing invocations cannot overwrite or remove each others' temporary files. Incidentally, this also fixes something else: The `+` character is not even a valid filename character on Windows. The only reason why Git for Windows did not need this is that above-mentioned POSIX emulation layer also plays a couple of tricks with filenames (tricks that are not interoperable with regular Windows programs, though), and previous attempts to remedy this in git/git were unsuccessful, see e.g. https://lore.kernel.org/git/pull.216.git.gitgitgadget@gmail.com/ This commit fixes one of the issues that are currently delaying Git for Windows v2.48.0-rc2. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Git for Windows
This is Git for Windows, the Windows port of Git.
The Git for Windows project is run using a governance model. If you encounter problems, you can report them as GitHub issues, discuss them on Git for Windows' Google Group, and contribute bug fixes.
To build Git for Windows, please either install Git for Windows'
SDK, start its git-bash.exe, cd
to your Git worktree and run make, or open the Git worktree as a folder in
Visual Studio.
To verify that your build works, use one of the following methods:
-
If you want to test the built executables within Git for Windows' SDK, prepend
<worktree>/bin-wrappersto thePATH. -
Alternatively, run
make installin the Git worktree. -
If you need to test this in a full installer, run
sdk build git-and-installer. -
You can also "install" Git into an existing portable Git via
make install DESTDIR=<dir>where<dir>refers to the top-level directory of the portable Git. In this instance, you will want to prepend that portable Git's/cmddirectory to thePATH, or test by running that portable Git'sgit-bash.exeorgit-cmd.exe. -
If you built using a recent Visual Studio, you can use the menu item
Build>Install git(you will want to click onProject>CMake Settings for Gitfirst, then click onEdit JSONand then pointinstallRootto themingw64directory of an already-unpacked portable Git).As in the previous bullet point, you will then prepend
/cmdto thePATHor run using the portable Git'sgit-bash.exeorgit-cmd.exe. -
If you want to run the built executables in-place, but in a CMD instead of inside a Bash, you can run a snippet like this in the
git-bash.exewindow where Git was built (ensure that theEOFline has no leading spaces), and then paste into the CMD window what was put in the clipboard:clip.exe <<EOF set GIT_EXEC_PATH=$(cygpath -aw .) set PATH=$(cygpath -awp ".:contrib/scalar:/mingw64/bin:/usr/bin:$PATH") set GIT_TEMPLATE_DIR=$(cygpath -aw templates/blt) set GITPERLLIB=$(cygpath -aw perl/build/lib) EOF -
If you want to run the built executables in-place, but outside of Git for Windows' SDK, and without an option to set/override any environment variables (e.g. in Visual Studio's debugger), you can call the Git executable by its absolute path and use the
--exec-pathoption, like so:C:\git-sdk-64\usr\src\git\git.exe --exec-path=C:\git-sdk-64\usr\src\git helpNote: for this to work, you have to hard-link (or copy) the
.dllfiles from the/mingw64/bindirectory to the Git worktree, or add the/mingw64/bindirectory to thePATHsomehow or other.
To make sure that you are testing the correct binary, call ./git.exe version
in the Git worktree, and then call git version in a directory/window where
you want to test Git, and verify that they refer to the same version (you may
even want to pass the command-line option --build-options to look at the
exact commit from which the Git version was built).
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.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt 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.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of core 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. The core git mailing list is plain text (no HTML!).
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