Multithreading

Introduction

The term “multithread programming” may sound complicated, but it is quite easy to do in C#.net. This article explains how multithreading works on your typical, general-purpose computer. You will learn how the operating system manages thread execution and how to manipulate the Thread class in your program to create and start managed threads. This article also renders the information you need to know when programming application with multiple threads such as Thread class, pools, threading issues and backgroundWorker.

Multithreading Overview

A thread is an independent stream of instructions in a program. Each written program is a paradigm of sequential programming in which they have a beginning, an end, a sequence, and a single point of execution. A thread is similar to sequential program. However, a thread itself is not a program, it can’t run on its own, but runs within a program.

The real concern surrounding threads is not about a single sequential thread, but rather the use of multiple threads in a single program all running at the same time and performing different tasks. This mechanism referred as Multithreading. A thread is considered to be a lightweight process because it runs within the context of a program and takes advantage of resources allocated for that program.

Threads are important both for client and server applications. While in C# program coding, when you type something in editor, the dynamic help (intellisense) Windows immediately shows the relevant topics that fit to the code. One thread is waiting for input from the user, while other does some background processing. A third thread can store the written data in a temporary file, while another one downloads a file from a specific location.

With the task manager, you can turn on the Thread column and see the processes and the number of threads for every process. Here, you can notice that only cmd.exe is running inside a single thread while all other applications use multiple threads.

The operating system schedules threads. A thread has priority and every thread has its own stack, but the memory for the program code and heap are shared among all threads of a single process.

A process consists of one or more threads of execution which is simply referred as threads. A process always consists of at least one thread called as Main thread (Main() method). A single thread process contains only one thread while multithread process can contains more than one thread of execution.

On a computer, the operating system loads and starts applications. Each application or service runs as a separate process on the machine. The following image illustrates that there are quite few processes actually running than there are applications. Many of the processes are background operating system processes that are started automatically when the computer powers up.

System.Threading Namespace

Under .NET platform, the System.Threading namespace provides a number of types that enable the direct construction of multithreaded application.

Type	Description
Thread	It represents a thread that execute within the CLR. Using this, we can produce additional threads in application domain.
Mutex	It is used for synchronization between application domains.
Monitor	It implements synchronization of objects using Locks and Wait.
Smaphore	It allows limiting the number of threads that can access a resource concurrently.
Interlock	It provides atomic operations for variables that are shared by multiple threads.
ThreadPool	It allows you to interact with the CLR maintained thread pool.
ThreadPriority	This represents the priority level such as High, Normal, Low.

System.Threading.Thread class

The Thread class allows you to create and manage the execution of managed threads in your program. They are called managed threads because you can directly manipulate each thread you create. You will found the Thread class along with useful stuffs in the System.Threading namespace.

Member	Type	Description
CurrentThread	Static	Return a reference of current running thread.
Sleep	Static	Suspend the current thread for a specific duration.
GetDoamin	Static	Return a reference of current application domain.
CurrentContext	Static	Return a reference of current context in which the thread currently running.
Priority	Instance level	Get or Set the Thread priority level.
IsAlive	Instance level	Get the thread state in form of True or False value.
Start	Instance level	Instruct the CLR to start the thread.
Suspend	Instance level	Suspend the thread.
Resume	Instance level	Resume a previously suspended thread.
Abort	Instance level	Instruct the CLR to terminate the thread.
Name	Instance level	Allows establishing a name to thread.
IsBackground	Instance level	Indicate whether a thread is running in background or not.