Thank you very much for the clear answer.  

I understood it.
I must think about another method if those are the specifications of Poser.

Because a so-called parallel computation is not my purpose, I do not care even about imitative thread of Python.
However, I grope for other method, at any rate.
 
As for me, I  wanted to implement the following user interface.

• There is long management to proceed automatically, and user does specific operation optionally.
• Or, a user needs to do nothing.  

Actually, my Python program which has such a user interface is working suitably outside Poser.
Of course a thread-safe mechanism is made consciously.

At any rate, I must reconsider design fundamentally to work it into Poser.

Thank you again.