Chapter 1: Defining Threads

---

Overview

Threading is the ability of a development framework to spin off parts of an application into "threads", which run out of step with the rest of the program. In most programming languages, you have the equivalent of a Main () method, and each line is executed in sequence, with the next line executing only after the previous has completed. A thread is a special object that is part of the general multitasking abilities of an operating system and allows a part of the application to run independently from the execution of other objects, and so out of the general execution sequence of the application. In this chapter, we will also discuss the different types of multitasking.

Another concept is that of free threading, which is not new to most C++ or Java developers; we will define this term and further explain the support provided in C#. We will briefly compare this free-threading model to other models, such as Visual Basic 6.0's apartment-threading model. We won't dwell on the differences for too long since this isn't a history lesson and this book certainly isn't about Visual Basic 6.0. However, understanding what sets these models apart will help you to understand why free threading is so wonderful. This chapter's concepts are essential to your understanding of the remainder of this book, as you will learn:

• What a thread is, conceptually

• Some comparisons between various multitasking and threading models

• Where threads exist and how they are allocated processor time

• How threads are controlled and managed using interrupts and priorities

• The concept of application domains, and how they provide finer grained control on the security of your application than that provided in a simple process environment

By understanding many of the concepts of threading and how they are structured in .NET, you will be better placed to make programming decisions on how to implement these features in your applications, before learning the details of implementation as provided in the rest of the book.

---