session.getRequest().getDegreeOfConcurrency(),
                    session.getProjects().size());
            // Propagate the parallel flag to the root session
            session.setParallel(threads > 1);
            this.executor = new PhasingExecutor(Executors.newFixedThreadPool(threads, new BuildThreadFactory()));

            // build initial plan
            this.plan = buildInitialPlan(taskSegments);