Programming Perl, 3rd Edition

Chapter 16. Interprocess Communication

Computer processes have almost as many ways of communicating as people do. The difficulties of interprocess communication should not be underestimated. It doesn't do you any good to listen for verbal cues when your friend is using only body language. Likewise, two processes can communicate only when they agree on the means of communication, and on the conventions built on top of that. As with any kind of communication, the conventions to be agreed upon range from lexical to pragmatic: everything from which lingo you'll use, up to whose turn it is to talk. These conventions are necessary because it's very difficult to communicate bare semantics in the absence of context.

In our lingo, interprocess communication is usually pronounced IPC. The IPC facilities of Perl range from the very simple to the very complex. Which facility you should use depends on the complexity of the information to be communicated. The simplest kind of information is almost no information at all: just the awareness that a particular event has happened at a particular point in time. In Perl, these events are communicated via a signal mechanism modeled on the Unix signal system.

At the other extreme, the socket facilities of Perl allow you to communicate with any other process on the Internet using any mutually supported protocol you like. Naturally, this freedom comes at a price: you have to go through a number of steps to set up the connections and make sure you're ...