.NET Framework Class Library
ThreadPriority Enumeration

Specifies the scheduling priority of a Thread.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)
Syntax

Visual Basic (Declaration)
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Enumeration ThreadPriority
Visual Basic (Usage)
Dim instance As ThreadPriority
C#
[SerializableAttribute]
[ComVisibleAttribute(true)]
public enum ThreadPriority
Visual C++
[SerializableAttribute]
[ComVisibleAttribute(true)]
public enum class ThreadPriority
JScript
public enum ThreadPriority
Members

Member nameDescription
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkLowestThe Thread can be scheduled after threads with any other priority.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkBelowNormalThe Thread can be scheduled after threads with Normal priority and before those with Lowest priority.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkNormalThe Thread can be scheduled after threads with AboveNormal priority and before those with BelowNormal priority. Threads have Normal priority by default.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkAboveNormalThe Thread can be scheduled after threads with Highest priority and before those with Normal priority.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkHighestThe Thread can be scheduled before threads with any other priority.
Remarks

ThreadPriority defines the set of all possible values for a thread priority. Thread priorities specify the relative priority of one thread versus another.

Every thread has an assigned priority. Threads created within the runtime are initially assigned the Normal priority, while threads created outside the runtime retain their previous priority when they enter the runtime. You can get and set the priority of a thread by accessing its Priority property.

Threads are scheduled for execution based on their priority. The scheduling algorithm used to determine the order of thread execution varies with each operating system. The operating system can also adjust the thread priority dynamically as the user interface's focus is moved between the foreground and the background.

The priority of a thread does not affect the thread's state; the state of the thread must be Running before the operating system can schedule it.

Examples

The following code example shows the result of changing the priority of a thread. Two threads are created and the priority of one thread is set to BelowNormal. Both threads increment a variable in a while loop and run for a set time.

Visual Basic
Option Explicit
Option Strict

Imports System
Imports System.Threading

Public Class Test

    <MTAThread> _
    Shared Sub Main()
        Dim priorityTest As New PriorityTest()

        Dim threadOne As Thread = _
            New Thread(AddressOf priorityTest.ThreadMethod)
        threadOne.Name = "ThreadOne"
        Dim threadTwo As Thread = _
            New Thread(AddressOf priorityTest.ThreadMethod)
        threadTwo.Name = "ThreadTwo"

        threadTwo.Priority = ThreadPriority.BelowNormal
        threadOne.Start()
        threadTwo.Start()

        ' Allow counting for 10 seconds.
        Thread.Sleep(10000)
        priorityTest.LoopSwitch = False
    End Sub

End Class

Public Class PriorityTest

    Dim loopSwitchValue As Boolean 

    Sub New()
        loopSwitchValue = True
    End Sub

    WriteOnly Property LoopSwitch As Boolean
        Set
            loopSwitchValue = Value
        End Set
    End Property

    Sub ThreadMethod()
        Dim threadCount As Long = 0

        While loopSwitchValue
            threadCount += 1
        End While

        Console.WriteLine("{0} with {1,11} priority " & _
            "has a count = {2,13}", Thread.CurrentThread.Name, _
            Thread.CurrentThread.Priority.ToString(), _
            threadCount.ToString("N0")) 
    End Sub

End Class
C#
using System;
using System.Threading;

class Test
{
    static void Main()
    {
        PriorityTest priorityTest = new PriorityTest();
        ThreadStart startDelegate = 
            new ThreadStart(priorityTest.ThreadMethod);

        Thread threadOne = new Thread(startDelegate);
        threadOne.Name = "ThreadOne";
        Thread threadTwo = new Thread(startDelegate);
        threadTwo.Name = "ThreadTwo";

        threadTwo.Priority = ThreadPriority.BelowNormal;
        threadOne.Start();
        threadTwo.Start();

        // Allow counting for 10 seconds.
        Thread.Sleep(10000);
        priorityTest.LoopSwitch = false;
    }
}

class PriorityTest
{
    bool loopSwitch;

    public PriorityTest()
    {
        loopSwitch = true;
    }

    public bool LoopSwitch
    {
        set{ loopSwitch = value; }
    }

    public void ThreadMethod()
    {
        long threadCount = 0;

        while(loopSwitch)
        {
            threadCount++;
        }
        Console.WriteLine("{0} with {1,11} priority " +
            "has a count = {2,13}", Thread.CurrentThread.Name, 
            Thread.CurrentThread.Priority.ToString(), 
            threadCount.ToString("N0")); 
    }
}
Visual C++
using namespace System;
using namespace System::Threading;
ref class PriorityTest
{
private:
   bool loopSwitch;

public:
   PriorityTest()
   {
      loopSwitch = true;
   }


   property bool LoopSwitch 
   {
      void set( bool value )
      {
         loopSwitch = value;
      }

   }
   void ThreadMethod()
   {
      __int64 threadCount = 0;
      while ( loopSwitch )
      {
         threadCount++;
      }

      Console::WriteLine( "{0} with {1,11} priority "
      "has a count = {2,13}", Thread::CurrentThread->Name, Thread::CurrentThread->Priority.ToString(), threadCount.ToString(  "N0" ) );
   }

};

int main()
{
   PriorityTest^ priorityTest = gcnew PriorityTest;
   ThreadStart^ startDelegate = gcnew ThreadStart( priorityTest, &PriorityTest::ThreadMethod );
   Thread^ threadOne = gcnew Thread( startDelegate );
   threadOne->Name =  "ThreadOne";
   Thread^ threadTwo = gcnew Thread( startDelegate );
   threadTwo->Name =  "ThreadTwo";
   threadTwo->Priority = ThreadPriority::BelowNormal;
   threadOne->Start();
   threadTwo->Start();

   // Allow counting for 10 seconds.
   Thread::Sleep( 10000 );
   priorityTest->LoopSwitch = false;
}

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
See Also

Reference

Other Resources

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