[Discuss-gnuradio] guide : what is the purpose of the gr_vmcircbuf.cc file and why it has been checked during the configuration process of the gnuradio.

[ton ph]

Hi everyone ,
I apologise in advance if i have asked a very insignificant and illogical question , I am trying to understand the gnuradio programming architecture so as i can make my own module/block so as i can implement and do some experiment on my concepts of dsp using gnuradio.Please someone guide me why the 
gr_vmcircbuf.cc is been checked in the configure.ac like 

AC_CONFIG_SRCDIR([gnuradio-core/src/lib/runtime/gr_vmcircbuf.cc]) 

in the top level configure.ac file.What it really is done in the gnuradio in the gnuradio.

Hope someone will be willing to teach me / guide me some of the problems coming from my side.
Thanks in advance.