C# Thread Priority in Multithreading
Last Updated :
11 Jul, 2025
Improve
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);
}
}
// 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..");
}
}
// 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..
