Difference between worker threads and general threads in BIND9

[christ lee]

In general, any server is designed as concurrent so that each thread
handles one incoming request. In Bind9 worker thread concept is there.
what is the differenec between this "worker thread" and the above thread.
named process runs continuously. suppose when a query comes like "
www.isc.org"
What part of the code is executed when answering this querie.

ThanQ