C# Thread Priority in Multithreading

Last Updated : 28 Jan, 2025

In a multithreaded environment, each thread has a priority that determines how frequently the thread is allocated CPU resources by the operating system. The Thread.Priority property in C# is used to set or get the priority of a thread.

A programmer can explicitly assign a priority to a thread using the Priority property.
By default, a thread’s priority is set to Normal.
The operating system handles thread scheduling, but priorities influence how threads are executed.
Setting priorities incorrectly can lead to thread starvation, where lower-priority threads may not get enough CPU time.
A high-priority thread does not guarantee that it will execute before a low-priority thread because of context switching and other OS-level scheduling mechanisms.
The thread priority always depends on the process priority (the parent container).

Thread Priority Levels

The ThreadPriority enum under the System.Threading namespace specifies the following priority levels:

Priority Level	Description	Value
Highest	Highest priority for a thread.	4
AboveNormal	Higher than Normal priority.	3
Normal (Default)	Default priority.	2
BelowNormal	Lower than Normal priority.	1
Lowest	Lowest priority for a thread.	0

Syntax:

public ThreadPriority Priority{ get; set; }

Exceptions:

ThreadStateException: If the thread has reached a final state, such as Aborted.
ArgumentException: If the value specified for a set operation is not a valid ThreadPriority value.

Example 1: This example demonstrates how to set and get the priority of threads.

// C# program to illustrate how to  // set and get the priority of threads  using System; using System.Threading;  class Geeks { 	static public void Main() 	{ 		// Creating and initializing threads  		Thread T1 = new Thread(work); 		Thread T2 = new Thread(work); 		Thread T3 = new Thread(work);  		// Set the priority of threads  		T2.Priority = ThreadPriority.Highest; 		T3.Priority = ThreadPriority.BelowNormal; 		T1.Start(); 		T2.Start(); 		T3.Start();  		// Display the priority of threads  		Console.WriteLine("The priority of T1 is: {0}", 		T1.Priority);  		Console.WriteLine("The priority of T2 is: {0}", 		T2.Priority);  		Console.WriteLine("The priority of T3 is: {0}", 		T3.Priority); 	}  	public static void work() 	{ 		// Sleep for 100 milliseconds 		Thread.Sleep(100); 	} }

Output

The priority of T1 is: Normal The priority of T2 is: Highest The priority of T3 is: BelowNormal

Example 2: This example demonstrates how thread priority can influence thread execution.

// C# program to illustrate the  // Priority property of Thread class  using System; using System.Threading;  class Geeks { 	static public void Main() 	{  		// Creating and initializing threads  		Thread T1 = new Thread(work1); 		Thread T2 = new Thread(work2);  		// Set the priority of threads  		// Here T2 thread executes first  		// because the Priority of T2 is  		// highest as compare to T1 thread  		T1.Priority = ThreadPriority.Lowest; 		T2.Priority = ThreadPriority.Highest; 		T1.Start(); 		T2.Start(); 	} 	public static void work1() 	{ 		Console.WriteLine("T1 thread is working.."); 	} 	public static void work2() 	{  		Console.WriteLine("T2 thread is working.."); 	} }

Output

T1 thread is working.. T2 thread is working..

C# Multithreading

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