Hello.
I got two questions about callback functions.

I'm wondering what happens if callback function has a blocking code inside
and gets automatically called back because of a newly arriving message when
the callback function is still busy. 

Another thing I'm unclear about callback functions is if there exists an
easy way to supply function input arguments to callback functions. Only
example I found that does this is using registerCallBack method. Is there a
easier way to supply function inputs?