[iam-dev] Incremental builder

["Michael Poindexter" <staticsnow@xxxxxxxxx>]

I've been looking at improving the speed of the IAM incremental builder.  It looks like much of the time we incur when doing a build is spent rebuilding classpaths.  I've got a prototype running locally that makes the following changes:

1.)  Move the builder out of JDT.  Instead, the builder lives in it's own plugin.  All classpath updating and maven invoking is moved out of the builder.  The builder plugin exposes an extension point to register IBuilderDelegates.  An IBuilderDelegate performs a specific task in response to events from the builder.  When the builder runs it diffs the POM, and fires events as necessary to registered builder delegates.  The current events are onParentPomChange, onParentPomReplace, onDependencyPomChange, onDependencyPomReplace, onPomChange, onPomReplace, onResourceChange, onFullBuild.  All of the onXXXChange methods are passed an object describing the changes made.  I've implemented a ResourceBuilderDelegate to handle our current resource processing (in the builder plugin), and a JDTBuilderDelegate (in the JDT plugin) to handle classpath updates.

2.)  The builder now caches its state on shutdown to avoid rebuilding the whole workspace the next startup.

3.)  To diff the poms I am using EMF Compare (http://www.eclipse.org/modeling/emft/?project=compare) operating on the POM model that was created for the POM editor.  

At work I have a pretty large workspace (~40 maven modules) which derive from a common base pom, and depend heavily on each other.  Before these changes if I made a change in a low level project or the base pom, or on startup I was having around 15 minutes of IAM building (ignoring the build time JDT had to do).  With this new structure it takes only a minute or two in the worst case (changing a dependency version in the base pom that effects all projects) (again, ignoring JDT build time in response to classpath changes), and very often takes no noticeably longer than a normal eclipse build.

Does this approach seem sound?  What about the new dependency on EMF Compare?  I think this simplifies the builder code greatly by allowing things like resource modification checking code to be completely separate from the classpath updating code.  In addition, this lets us support non-Java projects built with maven more easily in the future.  If the consensus is that the approach is sound I'll check my changes into a branch so everyone can review further as soon as I have time to do so.

Mike