@Override
    public String toString() {
        final String serverTasks = taskRegistry.toString();
        final StringBuilder sb = new StringBuilder();
        if (!serverTasks.isEmpty()) {
            sb.append("Server Tasks:\n");
            sb.append(serverTasks);
            sb.append("\n");
        }

        return sb.toString();
    }
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