(internal) starts **worker pool** threads or processes.

def _start_workers(self):
        """
        (internal) starts **worker pool** threads or processes.
        """
        # creating the pool of worker process or threads
        log.debug('%s starts a %s-pool of %s workers.' % \
                  (self, self.worker_type, self.worker_num))
        self.pool = []
        for host, worker_num in \
                           [(None, self.worker_num)] + list(self.worker_remote):
            for _worker in range(worker_num):
                __worker = Thread(target=_pool_worker, args=\
                                  (self._inqueue, self._outqueue, host)) \
                                  if self.worker_type == 'thread' else \
                           Process(target=_pool_worker, args=\
                                  (self._inqueue, self._outqueue, host))
                self.pool.append(__worker)
        for __worker in self.pool:
            __worker.daemon = True
            __worker.start()
        log.debug('%s started the pool' % self)