Equinox digraph ready for use

Previously I described how Virgo used OSGi framework hooks to implement a directed graph, or digraph, of isolated groups of bundles known as regions. The region digraph has now moved to Equinox and I'm modifying Virgo to use the Equinox region digraph in place of Virgo's own (see bug 343364 for details).

I always prefer making such changes in an incremental way, so the first step was to add the Equinox region digraph bundle to the Virgo kernel without exploiting it. The Virgo kernel runs fine with the Equinox region digraph in situ. This is because the Equinox digraph adds all bundles to its kernel region and so provides no isolation between those bundles. Later, Virgo's region digraph partitions the bundles in Virgo kernel and Virgo user regions with appropriate isolation and things continue to work as normal.

This is interesting, but not particularly useful. The whole point of the region digraph abstraction was to make it easy for multiple parties wishing to provide isolation via the OSGi framework hooks to be able to collaborate together by sharing and manipulating a single region digraph. It was never intended that multiple digraphs should co-exist.

But there is a useful point here. If you have an Equinox-based system, of which there are many, you can introduce the Equinox digraph with zero functional impact. All your bundles, including those installed before and after the Equinox region bundle, go in the Equinox kernel region and there is no isolation between those bundles.

When you want to start exploiting the digraph, you can use the RegionDigraph service to create a new region, attach it with appropriate filters, if any, to and from the kernel region, and then install a bundle into the new region using the Region.installBundle operation. After starting this bundle, you will then have a bundle context that can be used to install further bundles into the new region using the OSGi standard BundleContext API.

I hope this will inspire you to have a go at using the Equinox region digraph if you are an Equinox user and need to isolate groups of bundles.

Meanwhile, the standardisation of multi-bundle applications, including isolation, continues in the OSGi Alliance and a public draft of this spec should be available in the not too distant future. I hope the Equinox region digraph will be used more widely and this will help to provide feedback on the spec work.