Improving performance for Trac's git support

Using python bindings for git rather than the git command-line

This could be an alternative backend that would avoid the cost of spawning git executables and parsing their standard output.

The trade-offs could be the following, bindings vs. command-line:

• (+) faster (but how much?)
• (?) robustness
  • (+) no pipe handling and dangling processes (is this still problematic?)
  • (-) crashes?
• (-) memory usage (risk of memory leaks?)

Peter Stuge started a conversion of the backend, see his early work in his ​pygit2wip branch.

Note that the final form of the support for these bindings will have to come as a Trac plugin, much like TracMercurial is, as pygit2 is licensed under the GPL.

Installation

First you'll need to install the git bindings for Python:

• ​libgit2
• ​pygit2

And for building libgit2, you'll need ​cmake.

Windows build instructions, for Python 2.6 or 2.7 with VC9

$ git clone https://github.com/libgit2/libgit2.git
$ cd libgit2

Now set the LIBGIT2 environment variable to the place you want to install libgit2 (this environment variable is expected to be set by pygit2):

$ export LIBGIT2=C:/Dev/libgit2-vc9

if you live in a msysgit bash shell, or:

> set LIBGIT2=C:/Dev/libgit2-vc9

if you're forced to use a cmd.exe…

Then download the libgit2-msvc9.diff​ patch, apply it, build and install libgit2 like this:

$ patch -p1 < libgit2-msvc9.diff
$ mkdir build-msvc9
$ cd build-msvc9
$ cmake -G "Visual Studio 9 2008" .. -DCMAKE_INSTALL_PREFIX=$LIBGIT2
-- Check for working C compiler using: Visual Studio 9 2008
-- Check for working C compiler using: Visual Studio 9 2008 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Found PythonInterp: C:/Dev/Python272/python.exe (found version "2.7.2")
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Workspace/src/git/libgit2/build-msvc9
$ cmake --config Release --build . --target install

(replace $LIBGIT2 with %LIBGIT2% if you're in a cmd.exe)

At this point you're ready to build the bindings themselves. First download pygit2-msvc9.diff​, then:

$ git clone https://github.com/libgit2/pygit2
$ cd pygit2
$ patch -p1 < pygit2-msvc9.diff
$ ls $LIBGIT2
bin include lib
$ python setup.py install

Note about the tests:

$ python setup.py test --args\ -v

with 0.17, I get one error (test_read_tree) and … several crashes (test_new_repo, test_write, test_status, and nearly all tests in test_diff.py).