How can I control the number of CPU threads used by the environment?

I notice that some environments in the DMControl suite may take more than one CPU thread.
For example, if we choose Domain_name=finger, Task_name=spin.

I run this task in a server with 40 threads Intel(R) Xeon(R) CPU E5-2640 v4 @ 2.40GHz and 4 Titan XP. This task takes 8 threads when starting. Then it will take 3 CPU threads when train my agent.

I run this task in a server with 32 threads Intel(R) Xeon(R) Gold 6137 CPU @ 3.90GHz and 4Titan RTX. This takes 12 threads when starting. Then it will take 12 CPUs threads as training.

And different tasks may take different threads. For example, if we start Domain_name=ball_in_cup, Task_name=catch, then it takes 16 threads as training.

It is a heavy computational burden if the task takes too much CPU resources.

So, how can I control the number of CPU threads used by the environment of DMControl suite?

Thank you and best wishes.