Multithreading Part I: Multithreading and Multitasking

In this and a series of articles that would follow, we would learn about threads and how to write multi-threaded programs in C#. 

In this article we would learn what threads are and why they are needed. In part2 we would learn about threading with respect to the .NET framework. At the end of this article series you would have learnt how to create and manage threads, set thread priorities, determine thread states, thread pooling and thread synchronization.

Introduction

When the computers were first invented, they were capable of executing one program at a time. Thus once one program was completely executed, they then picked the second one to execute and so on. With time, the concept of timesharing was developed whereby each program was given a specific amount of processor time and when its time got over the second program standing in queue was called upon (this is called Multitasking, and we would learn more about it soon). Each running program (called the process) had its own memory space, its own stack, heap and its own set of variables. One process could spawn another process, but once that occurred the two behaved independent of each other. Then the next big thing happened. The programs wanted to do more than one thing at the same time (this is called Multithreading, and we would learn what it is soon). A browser, for example, might want to download one file in one window, while it is trying to upload another and print some other file. This ability of a program to do multiple things simultaneously is implemented through threads (detailed description on threads follows soon).

Multitasking vs. Multithreading

As explained above, Multitasking is the ability of an operating system to execute more than one program simultaneously. Though we say so but in reality no two programs on a single processor machine can be executed at the same time. The CPU switches from one program to the next so quickly that appears as if all of the programs are executing at the same time. Multithreading is the ability of an operating system to execute the different parts of the program, called threads, simultaneously. The program has to be designed well so that the different threads do not interfere with each other. This concept helps to create scalable applications because you can add threads as and when needed. Individual programs are all isolated from each other in terms of their memory and data, but individual threads are not as they all share the same memory and data variables. Hence, implementing multitasking is relatively easier in an operating system than implementing multithreading.

Hey, wait!!! all that’s fine but I still do not understand fully what threads are!!!