.NET Framework Class Library
ProcessThread..::.ProcessorAffinity Property

Updated: August 2008

Sets the processors on which the associated thread can run.

Namespace:  System.Diagnostics
Assembly:  System (in System.dll)
Syntax

Visual Basic (Declaration)
<BrowsableAttribute(False)> _
Public WriteOnly Property ProcessorAffinity As IntPtr
Visual Basic (Usage)
Dim instance As ProcessThread
Dim value As IntPtr

instance.ProcessorAffinity = value
C#
[BrowsableAttribute(false)]
public IntPtr ProcessorAffinity { set; }
Visual C++
[BrowsableAttribute(false)]
public:
property IntPtr ProcessorAffinity {
    void set (IntPtr value);
}
JScript
public function set ProcessorAffinity (value : IntPtr)

Property Value

Type: System..::.IntPtr
An IntPtr that points to a set of bits, each of which represents a processor that the thread can run on.
Exceptions

ExceptionCondition
Win32Exception

The processor affinity could not be set.

PlatformNotSupportedException

The platform is Windows 98 or Windows Millennium Edition.

NotSupportedException

The process is on a remote computer.

Remarks

The processor affinity of a thread is the set of processors it has a relationship to. In other words, those it can be scheduled to run on.

ProcessorAffinity represents each processor as a bit. Bit 0 represents processor one, bit 1 represents processor two, and so on. The following table shows a subset of the possible ProcessorAffinity for a four-processor system.

Property value (in hexadecimal)

Valid processors

0x0001

1

0x0002

2

0x0003

1 or 2

0x0004

3

0x0005

1 or 3

0x0007

1, 2, or 3

0x000F

1, 2, 3, or 4

You can also specify the single, preferred processor for a thread by setting the IdealProcessor property. A process thread can migrate from processor to processor, with each migration reloading the processor cache. Specifying a processor for a thread can improve performance under heavy system loads by reducing the number of times the processor cache is reloaded.

Examples

The following example shows how to set the ProcessorAffinity property for an instance of Notepad to the first processor.

Visual Basic
Imports System
Imports System.Diagnostics



Class Program

    Shared Sub Main(ByVal args() As String) 
        ' Make sure there is an instance of notepad running.
        Dim notepads As Process() = Process.GetProcessesByName("notepad")
        If notepads.Length = 0 Then
            Process.Start("notepad")
        End If
        Dim threads As ProcessThreadCollection
        'Process[] notepads;
        ' Retrieve the Notepad processes.
        notepads = Process.GetProcessesByName("Notepad")
        ' Get the ProcessThread collection for the first instance
        threads = notepads(0).Threads
        ' Set the properties on the first ProcessThread in the collection
        threads(0).IdealProcessor = 0
        threads(0).ProcessorAffinity = CType(1, IntPtr)
    End Sub 'Main
End Class 'Program
C#
using System;
using System.Diagnostics;

namespace ProcessThreadIdealProcessor
{
    class Program
    {
        static void Main(string[] args)
        {
            // Make sure there is an instance of notepad running.
            Process[] notepads = Process.GetProcessesByName("notepad");
            if (notepads.Length == 0)
                Process.Start("notepad");
            ProcessThreadCollection threads;
            //Process[] notepads;
            // Retrieve the Notepad processes.
            notepads = Process.GetProcessesByName("Notepad");
            // Get the ProcessThread collection for the first instance
            threads = notepads[0].Threads;
            // Set the properties on the first ProcessThread in the collection
            threads[0].IdealProcessor = 0;
            threads[0].ProcessorAffinity = (IntPtr)1;
        }
    }
}
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

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
See Also

Reference

Change History

Date

History

Reason

August 2008

Added an example.

Customer feedback.

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