Simplifying The p2 Process, Part 1: p2 Composite Repos

With the release of JBoss Tools 3.2 and JBoss Developer Studio 4.0 just around the corner, you may be thinking to yourself, "Self, how many update sites and SDK zips and runtimes will I need to download THIS time?"

Or maybe you're thinking, "Self, why is this so damn complicated?"

Well, folks, we heard your kvetching and we did something about it.

Composite Repos

While this is not a new concept to many, we embraced the composite update site this past year and it's made life a lot easier for iterative, agile development cycles. Last year, JBoss Tools 3.1 was built as a single Hudson job, with a second one for JBoss Developer Studio. This meant that any change in any of the components would cause a build to be launched, and 4-6hrs later, we'd have fresh bits. Yeah, far from ideal.

This year, we split up the monolith (and added a few new components!) so that now we have 34 update sites to compose into a single one against which builds can then be built. This composite update site looks like this:

compositeArtifacts.xml

<?xml version='1.0' encoding='UTF-8'?>
<?compositeArtifactRepository version='1.0.0'?>
<repository name='JBoss Tools Staging Repository' 
  type='org.eclipse.equinox.internal.p2.artifact.repository.CompositeArtifactRepository' 
  version='1.0.0'>
<properties size='2'>
<property name='p2.compressed' value='true'/>
<!-- get new time w/ `date +%s000` -->
<property name='p2.timestamp' value='1294205433000'/>
</properties>
<children size='34'>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-3.2_trunk.component--archives/all/repo/'/>
...
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-3.2_trunk.component--ws/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-pi4soa-3.1_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-teiid-designer-7.1_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-drools-5.2_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-savara-1.1_trunk/tools/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/xulrunner-1.9.1.2/all/repo/'/>
</children>
</repository>

compositeContent.xml

<?xml version='1.0' encoding='UTF-8'?>
<?compositeMetadataRepository version='1.0.0'?>
<repository name='JBoss Tools Staging Repository' 
  type='org.eclipse.equinox.internal.p2.metadata.repository.CompositeMetadataRepository' 
  version='1.0.0'>
<properties size='2'>
<property name='p2.compressed' value='true'/>
<!-- get new time w/ `date +%s000` -->
<property name='p2.timestamp' value='1294205433000'/>
</properties>
<children size='34'>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-3.2_trunk.component--archives/all/repo/'/>
...
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-3.2_trunk.component--ws/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-pi4soa-3.1_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-teiid-designer-7.1_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-drools-5.2_trunk/all/repo/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/jbosstools-savara-1.1_trunk/tools/'/>
<child location='http://download.jboss.org/jbosstools/builds/staging/xulrunner-1.9.1.2/all/repo/'/>
</children>
</repository>

So, now that JBoss Tools is built in 34 pieces, the bits that haven't changed aren't rebuilt over and over and builds are faster. If that sounds insanely obvious to you, well, we used to have a lot of inter-component cyclic dependencies. We eliminated those early in the development cycle for JBoss Tools 3.2, and have been able to build smarter and faster ever since.

Added benefits to this composite site are:

• Newly built and published bits are instantly available from the composite site - sure, the same was true under last year's PDE "uberbuild" regime, but that's because everything was built fresh every time, which was slow and near-impossible to get people to run at home.

• Developers can use this site to install latest updates to components they're interested in testing - again, this was true before; but now using the same site and searching for updates, developers and beta testers can get incremental updates to the components that have actually changed, rather than having to pull down 160M every day to get a few K of changes.

• Tycho can be pointed at this site (see below) in order to resolve binary p2 dependencies, so building a component deep in the dependency chain can be done w/o having to first build its upstream dependencies - this wasn't a concern before because everything was built from source every time, so by definition everything was already on disk. But now, if a developer only cares about a single component, like ModeShape or GWT, they need only have that source (and some bootstrapping code) on disk. Smaller, faster, more agile. And way more likely to be built locally before checking in code than before, making the painful "who broke what and when?" process much less painful. Fewer moving pieces and local dev builds at home mean - in theory - fewer incomplete or breaking commits.

When we first moved to Tycho, we needed to build a series of components locally in order to just get to a deep component. For example, the Struts component needs VPE, which needs JST and XulRunner. JST also needs the Common component, which in turn needs the Tests component.

So, to build Struts locally, 5 other components would have to be built locally first. This worked, but was still a fairly large barrier to entry for most developers (much less contributors!)

But with this new composite site, building Struts can be done without this lengthy bootstrapping; instead we just point Tycho at this composite site, and it pulls down the 5 upstream components' jars from this p2 repo - because the upstream deps are already built in Hudson.

Here's what we added to our parent pom.xml to have the builds find the binaries:

<repository>
        <id>jbosstools-nightly-staging-composite-trunk</id>
        <url>http://path.to.the.site/staging/_composite_/trunk/ </url>
        <layout>p2</layout>
        <snapshots>
                <enabled>true</enabled>
        </snapshots>
        <releases>
                <enabled>true</enabled>
        </releases>
</repository>

So, using this composite update site, we can use Maven 3 with Tycho 0.10 to generate a single update site (staged here, then ultimately published here).

---

In part 2, I'll look at why we switched from using a collection of SDKs (Eclipse, EMF, DTP, GEF, M2E, RSE, TPTP, UMl2, WTP, XSD and more) against which to build - using the now-deprecated brute-force "just unzip into eclipse root folder or dropins" approach - to using a single target platform update site. SPOILER ALERT: Easier to update and maintain.

In part 3, I'll look back at the success we've had using associate sites instead of asking people to manually add 3rd party URLs when installing JBoss Tools. SPOILER ALERT: one URL is easier for people to use than 6.

In part 4, I'll talk a little about how to prevent your product build from getting updates from unofficial sources, and preload your product with the official sites from which to get updates. Because it's important to balance ease of use with prevention of unsupported features. SPOILER ALERT: may contain p2.inf instructions.

By the way, JBoss Tools 3.2.0.CR1 and JBoss Developer Studio 4.0.0.CR1 are available. Get 'em while they're hot (and sourceforge is not).