I've let a personal "git education" project languish for a month or more. Recently I became energized for the project again and wanted to perform some more experiments.

Hudson - Continuous Integration

One of the things that energized me was the realization that a personal project has much in common with work projects. I want to know all the time that it is in good condition, and I want to know as soon as possible if it is not in good condition. For me, that meant I wanted a continuous integration setup, one that would compile and test the code every time I made a change.

At work we organically grew our own continuous integration setup over the course of five years. It met our needs, and didn't have too many features we didn't need.

During those same five years, the open source community has been creating interesting software in the same space. CruiseControl (from ThoughtWorks) and Hudson (from Sun) are two open souce continuous integration projects that I had seen. CruiseControl is used on a new project at work. I wanted to try something different, so I started an experiment with Hudson.

Hudson was simple to install on my Linux computer, simple to configure from a web browser interface, and seemed to work well in my environment. I watched the first compilation run pass, and thought things had worked brilliantly.

Null Pointer Exception in Git SCM Plugin

Unfortunately, the second time I tried to start a continuous integration run from Hudson, there had been no intervening changes to the git repository. That exercised a bug in the Git plugin and I was left with an ugly message about a null pointer exception on line 43 of the Git plugin.

Another Excuse to Learn

I wanted to learn more about Hudson, and I thought it would be cool to contribute a bug fix back to the community for that null pointer exception. It couldn't be that hard...

I read the instructions for building Hudson, installed Apache Maven 2 (as required by Hudson), downloaded the Hudson source code, and compiled it. Unfortunately, the Hudson compilation did not compile the Git plugin. As I read the plugin source code, the line which had the null pointer exception was a blank line. That meant the source had advanced beyond the code which was compiled in the git plugin I was using. Maybe the bug was already fixed...

A little searching on the web suggested that I might be able to build the plugin by changing to the plugins/git directory in the souce tree and running Maven ("mvn"). That worked. I copied the new Git plugin into my ~/.hudson/plugins directory, and restarted Hudson.

The new Git plugin worked great, with no null pointer exception.

More Progress, More Fun

I've now watched the Hudson system run 8 builds since I installed it less than 2 days ago. It runs the builds after it detects a checkin, without requiring any thought from me. The results are easily seen in a web page, the configuration is done through web pages, and the whole process felt seamless and elegant.

All that, and the software is free...

Next Steps

I have a whole bunch of other ideas to improve my little development environment. I'll add test execution in the Hudson environment, and move the Hudson environment to another machine, and make Hudson run all the time, and have all sorts of fun watching it.

I've already configured a second Hudson job on my little machine. The second job monitors my copy of the git source code. If there is a change to that source (usually because I did a "git pull" from the master sources), then the new code is built and the results of the build are available as summaries and as details.