They don’t known each other. It will be good if module thread can post message to lisp thread. It will be better if module thread can send lisp data within the message to lisp thread. 

If json messages are parsed in module thread and saved as c struct data(not lisp data), they have to be
translated to lisp data before emacs use. The translation which should be done in emacs thread cost too
much cpu, which make the parallel parsing of json messages not very useful.

You are saying that the translation is costly, but did someone
actually measure that and verify that it's indeed costly? And if
someone did, where can I see the results in sufficient level of detail
to understand what part(s) of parsing JSON are the bottleneck?

Is it possible to parse json messages and prepare data struct for pdumper, and translate the data to lisp
using pdumper? What about the performanse comparing with the above?

I don't think I understand what does pdumper have to do with this
issue.