What is my_init_fcn_t stands for in the source code

I’m trying to understand the source code and since there is no documentation about the source, i hope you can help me here.
there is two functions on the main.cpp in the root project directory. one of them will be compiled depending on defining macro AS_SERVICE
there is a little confusion on the first lines of the main.cpp
why do you declare MAINNAME function while AS_SERVICE macro is declared but my_init_fcn_t while not?!
what’s the different?!
when should i declare AS_SERVICE for compiling?!(What differences does it make? )