LibEvent, signals or communication between threads

[Shadow_exe]

Hello everyone.
Faced with an interesting challenge, and how to solve it and 
found no tracks.
The problem is the following:
I have 2 thread, which are created in the main flow, 
respectively, of each other, they do not know, but I want to 
create a dialogue between the thread. I want to first thread 
could tell the second thread to perform some function.
The queue is implemented through a library libevent.

Who faced a similar problem or just knows how to solve this issue 
- please help.