Java Network Programming, 4th Edition

Chapter 3. Threads

Back in the good old days of the Net, circa the early 1990s, we didn’t have the Web and HTTP and graphical browsers. Instead, we had Usenet news and FTP and command-line interfaces, and we liked it that way! But as good as the good old days were, there were some problems. For instance, when we were downloading kilobytes of free software from a popular FTP site over our 2,400 bps modems using Kermit, we would often encounter error messages like this one:

% ftp eunl.java.sun.com
Connected to eunl.javasoft.com.
220 softwarenl FTP server (wu-2.4.2-academ[BETA- 16]+opie-2.32(1) 981105)
    ready.
Name (eunl.java.sun.com:elharo): anonymous
530-
530-    Server is busy.  Please try again later or try one of our other
530-    ftp servers at ftp.java.sun.com.  Thank you.
530-
530 User anonymous access denied.
Login failed.

In fact, in the days when the Internet had only a few million users instead of a few billion, we were far more likely to come across an overloaded and congested site than we are today. The problem was that most FTP servers forked a new process for each connection (i.e., 100 simultaneous users meant 100 additional processes to handle). Because processes are fairly heavyweight items, too many could rapidly bring a server to its knees. The problem wasn’t that the machines weren’t powerful enough or the network fast enough; it was that the FTP servers were poorly implemented. Many more simultaneous users could be served if a new process wasn’t needed for each connection. ...