After adding a set of projects to a Continuum 1.2 instance, the server stopped performing any builds on any projects. CPU usage shoots up to 100%, projects are queued up and are apparently started, but no build processes are invoked. Even the simplest pom-only job times out.
Looking at the database I noticed that the last entry for the top-queued project in the BUILDRESULT table had an END_TIME of 0. When I changed that field to a current time and restarted the server Continuum started to perform builds again.
I was able to duplicate the problem by setting the END_TIME of the last BUILDRESULT of a project to 0, starting the server, and waiting for that project to be queued. The problem was resolved again when I reset END_TIME to its original value.
I've attached a thread dump as suggested on users@continuum. It seems to show that Continuum is in the SCM module's ChangeSet.toString(), which doesn't seem right, but perhaps it will help point to the root cause.