Write the following TCP server programs: (Do all of this in C langauge )
a. Concurrent server program with multiple processes (using fork system call)
b. Concurrent server program with multiple threads (using pthreads)
c. Non-blocking server programs that implement I/O multiplexing using

i. select() system call
ii. poll() system call
iii. epoll API

All non-blocking designs must support 4000 concurrent connections (i.e.,
listener file descriptors).