Question

How does a web-server serve its client using the same port(80) for a TCP connection. For a UDP connection, i understand that there is no connection, per se, so we can have multiple clients send packets to same port. If i try to use an already used port on my localhost, i get BindException.

One solution i see to this is starting a thread for each connection, but wouldnt this be cumbersome for site like google/yahoo where there a >100000 connections in each server?

What solutions do web servers employ for this problem?

Answer 1

Server listens on a well-known port (80) and delegate the request to a worker socket once it receive the request. That way it can serve the next request. You can write your own simple server to understand whats going on. Oracle site has a nice example code. [1]

[1] http://java.sun.com/developer/technicalArticles/Networking/Webserver/WebServer.java

first it creates a server socket;

ServerSocket ss = new ServerSocket(port);

then it listnes on the specified port and create a new socket once it accepts the request;

Socket s = ss.accept();

As shown in the code, it has a worker thread pool, so at a given moment you can control the number of request get served by the server at a given time. Others wait in a Queue may be.