@Override
    public boolean isTerminated(final TaskId taskId) {
        final TaskContextImpl taskContext = taskRegistry.get(taskId);
        if (taskContext != null) {
            return taskContext.isTerminated();
        }
        return true;
    }
Tells tasks to terminate and waits for all tasks to terminate before
cleaning up the executors.
stroom-task/stroom-task-impl/src/main/java/stroom/task/impl/TaskManagerImpl.java