Java Threads, Second Edition

Thread Overview

This leaves us only one more term to define: what exactly is a thread? The term thread is shorthand for thread of control, and a thread of control is, at its simplest, a section of code executed independently of other threads of control within a single program.

Thread of Control

Thread of control sounds like a complicated technical term, but it’s really a simple concept: it is the path taken by a program during execution. This determines what code will be executed: does the if block get executed, or does the else block? How many times does the while loop execute? If we were executing tasks from a “to do” list, much as a computer executes an application, what steps we perform and the order in which we perform them is our path of execution, the result of our thread of control.

Having multiple threads of control is like executing tasks from two lists. We are still doing the tasks on each “to do” list in the correct order, but when we get bored with the tasks on one of the lists, we switch lists with the intention of returning at some future time to the first list at the exact point where we left off.

Overview of Multitasking

We’re all familiar with the use of multitasking operating systems to run multiple programs simultaneously. Each of these programs has at least one thread within it, so at some level, we’re already comfortable with the notion of a thread in a single process. The single-threaded process has the following properties, which, as it turns out, are shared ...