为什么要使用非阻塞或阻塞套接字?

At first, I must ask that which is the best in which states ? For example a real-time MMORPG server. What if i create a thread per client instead of using non-blocking sockets ? Or What if i use one thread that contains all non-blocking sockets ? Can you explain me the advantages ?At first, I must ask that which is the best in