We use ndbd at data node(single thread mode), but found 34 threads of ndbd (no replies)

We use ndbd (not ndbtmd) at data node, but found 34 threads of ndbd.
I think ndbd is a single thread process, why there are so threads of ndbd?
So there is no need to change ndbd to ndbtmd?

ps -eT | grep ndbd

20374 20374 ? 6-16:36:00 ndbd
20374 20375 ? 00:04:49 ndbd
20374 20376 ? 00:04:35 ndbd
20374 20377 ? 00:00:38 ndbd
20374 20378 ? 00:06:24 ndbd
20374 20379 ? 00:06:30 ndbd
20374 20380 ? 00:03:50 ndbd
20374 20381 ? 00:06:19 ndbd
20374 20382 ? 00:02:51 ndbd
20374 20383 ? 00:00:00 ndbd
20374 20384 ? 00:00:00 ndbd
20374 20385 ? 00:05:51 ndbd
20374 20386 ? 00:02:45 ndbd
20374 20387 ? 00:06:28 ndbd
20374 20388 ? 00:03:32 ndbd
20374 20389 ? 00:03:31 ndbd
20374 20390 ? 00:06:21 ndbd
20374 20391 ? 00:00:00 ndbd
20374 20392 ? 00:00:42 ndbd
20374 20393 ? 00:00:00 ndbd
20374 20394 ? 00:00:00 ndbd
20374 20395 ? 00:00:00 ndbd
20374 20396 ? 00:01:58 ndbd
20374 20397 ? 00:06:33 ndbd
20374 20398 ? 00:06:26 ndbd
20374 20399 ? 00:04:51 ndbd
20374 20400 ? 00:06:20 ndbd
20374 20401 ? 00:06:37 ndbd
20374 20402 ? 00:06:23 ndbd
20374 20403 ? 00:06:28 ndbd
20374 20404 ? 00:01:25 ndbd
20374 20405 ? 00:01:22 ndbd
20374 20406 ? 00:00:00 ndbd
20374 20407 ? 00:00:00 ndbd
29336 29336 ? 00:42:15 ndbd