'Start ``nworkers`` worker threads.'

def _init_worker_threads(self):

    self.work_queue = Queue()
    self.work_threads = []
    log.debug(('Starting    %s    %s    workers' % (self.nworkers, self.runner_name)))
    for i in range(self.nworkers):
        worker = threading.Thread(name=('%s.work_thread-%d' % (self.runner_name, i)), target=self.run_next)
        worker.setDaemon(True)
        worker.start()
        self.work_threads.append(worker)
