Sockets

1. What are sockets?

   Sockets provide an interface to network protocols. Their purpose is to make network programming simpler than programming directly to the network protocol. Sockets most often use TCP/IP as the underlying protocol, but can use virtually any of the common network protocols.

2. How do sockets function?

   There are several modes of operation available for sockets, but a very common mode is to establish a socket listener that listens on some port, say 4040, for connection requests. When a socket client, from another process or a remote computer, requests a connection on port 4040, the listener spawns a new thread that starts up a socket server on a new port, say 5051. From that time on the socket client and socket server communicate on port 5051. Either one can send data, in the form of a group of bytes, to the other. Meanwhile the listener goes back to listening for connection requests on port 4040.

   

   The receiving socket, either client or server, has a buffer that stores bytes of data until the receiver thread reads them. If the receiver buffer becomes full, the sender thread will block on a send call until the receiver reads some of the data out of the buffer. For this reason, it is a good idea to assign a thread in the receiver to empty the buffer and enqueue the data for a worker thread to digest.