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SetProcessAffinityMask API

This code allows you to set the process affinity on a running thread for multi processor computers.
Get the process ID of a running thread by filename. Get the process handle by the PID. Set your custom Affinity Mask. Apply the affinity mask to the process thread.

Original Author: Justin Ploski


Process Name is the only variable input.
You'll need to customize the affinity mask - see comments by the MyMask assignment for information.


This code is Windows API that allows you to specify a running process name and obtain the PID (Process ID). From the PID, it then obtains a handle on the process. You then set a custom affinity BitMask for the process, and pass the handle and affinity mask to the SetProcessAffinity function. Use GetCurrentProcess() API (always returns long -1) in place of the application handle to set the affinity on the current application.
See the comments when setting the MyMask variable to customize which processors will be used.
This is my first submission. I've been leeching off PlanetSourceCode for years, so I figured it's time to give something back. I've seen alot of questions but not many answers related to process affinity for multiprocessors. Please comment if you find this code useful.


The SetProcessAffinity API returns 0 if the affinity was set correctly. Anything <> 0 is an error.

Side Effects

If using a single processor machine, the only valid process affinity is CPU0.

API Declarations

Option Explicit
Private Declare Function WTSEnumerateProcesses Lib "wtsapi32.dll" Alias "WTSEnumerateProcessesA" (ByVal hServer As Long, ByVal Reserved As Long, ByVal Version As Long, ByRef ppProcessInfo As Long, ByRef pCount As Long) As Long
Private Declare Function SetProcessAffinityMask Lib "kernel32.dll" (ByVal hProcess As Long, ByVal dwProcessAffinityMask As Long) As Long
Private Declare Function OpenProcess Lib "kernel32.dll" (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, ByVal dwProcId As Long) As Long
Private Declare Sub WTSFreeMemory Lib "wtsapi32.dll" (ByVal pMemory As Long)
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
SessionID As Long
ProcessID As Long
pProcessName As Long
pUserSid As Long
End Type


Public Sub Main()
Call SetAffinityByEXE("notepad.exe")
End Sub
Private Sub SetAffinityByEXE(strImageName As String)

Const MAX_PATH = 260
Const SYNCHRONIZE = &H100000
Const hNull = 0
Const WIN95_System_Found = 1
Const WINNT_System_Found = 2
Const Default_Log_Size = 10000000
Const Default_Log_Days = 0

Dim BitMasks() As Long, NumMasks As Long, LoopMasks As Long
Dim MyMask As Long
Const AffinityMask As Long = &HF ' 00001111b

Dim lngPID As Long
Dim lngHwndProcess
lngPID = GetProcessID(strImageName)
If lngPID = 0 Then
MsgBox "Could not get process ID of " & strImageName, vbCritical, "Error"
Exit Sub
End If
lngHwndProcess = OpenProcess(PROCESS_ALL_ACCESS, 0, lngPID)
If lngHwndProcess = 0 Then
MsgBox "Could not obtain a handle for the Process ID: " & lngPID, vbCritical, "Error"
Exit Sub
End If
BitMasks() = GetBitMasks(AffinityMask)

'Use CPU0
MyMask = BitMasks(0)

'Use CPU1
'MyMask = BitMasks(1)

'Use CPU0 and CPU1
'MyMask = BitMasks(0) Or BitMasks(1)

'The CPUs to use are specified by the array index.
'To use CPUs 0, 2, and 4, you would use:
'MyMask = BitMasks(0) Or BitMasks(2) Or BitMasks(4)

'To Set Affinity, pass the application handle and your custom affinity mask:
'SetProcessAffinityMask(lngHwndProcess, MyMask)
'Use GetCurrentProcess() API instead of lngHwndProcess to set affinity on the current app.
If SetProcessAffinityMask(lngHwndProcess, MyMask) = 1 Then
MsgBox "Affinity Set", vbInformation, "Success"
MsgBox "Failed To Set Affinity", vbCritical, "Failure"
End If

End Sub
Private Function GetBitMasks(ByVal inValue As Long) As Long()
Dim RetArr() As Long, NumRet As Long
Dim LoopBits As Long, BitMask As Long
Const HighBit As Long = &H80000000
ReDim RetArr(0 To 31) As Long
For LoopBits = 0 To 30
BitMask = 2 ^ LoopBits
If (inValue And BitMask) Then
RetArr(NumRet) = BitMask
NumRet = NumRet + 1
End If
Next LoopBits
If (inValue And HighBit) Then
RetArr(NumRet) = HighBit
NumRet = NumRet + 1
End If
If (NumRet > 0) Then ' Trim unused array items and return array
If (NumRet < 32) Then ReDim Preserve RetArr(0 To NumRet - 1) As Long
GetBitMasks = RetArr
End If
End Function
Private Function GetProcessID(strProcessName As String) As Long
Dim RetVal As Long
Dim Count As Long
Dim i As Integer
Dim lpBuffer As Long
Dim p As Long
Dim udtProcessInfo As WTS_PROCESS_INFO

Dim lngProcessID As Long
Dim strTempProcessName As String
RetVal = WTSEnumerateProcesses(WTS_CURRENT_SERVER_HANDLE, 0&, 1, lpBuffer, Count)
If RetVal Then ' WTSEnumerateProcesses was successful
p = lpBuffer
For i = 1 To Count
' Count is the number of Structures in the buffer
' WTSEnumerateProcesses returns a pointer, so copy it to a
' WTS_PROCESS_INO UDT so you can access its members
CopyMemory udtProcessInfo, ByVal p, LenB(udtProcessInfo)
' Add items to the ListView control

lngProcessID = CLng(udtProcessInfo.ProcessID)

' Since pProcessName contains a pointer, call GetStringFromLP to get the
' variable length string it points to
If udtProcessInfo.ProcessID = 0 Then
  'MsgBox "System Idle Process"
  strTempProcessName = GetStringFromLP(udtProcessInfo.pProcessName)
  If UCase(strTempProcessName) = UCase(strProcessName) Then
  GetProcessID = lngProcessID
  End If
End If

p = p + LenB(udtProcessInfo)
Next i
WTSFreeMemory lpBuffer 'Free your memory buffer
MsgBox "Error", vbCritical, "Fatal Error"
End If
End Function
Private Function GetStringFromLP(ByVal StrPtr As Long) As String
Dim b As Byte
Dim tempStr As String
Dim bufferStr As String
Dim Done As Boolean
Done = False
' Get the byte/character that StrPtr is pointing to.
CopyMemory b, ByVal StrPtr, 1
If b = 0 Then ' If you've found a null character, then you're done.
Done = True
tempStr = Chr$(b) ' Get the character for the byte's value
bufferStr = bufferStr & tempStr 'Add it to the string

StrPtr = StrPtr + 1 ' Increment the pointer to next byte/char
End If
Loop Until Done
GetStringFromLP = bufferStr
End Function

About this post

Posted: 2002-06-01
By: ArchiveBot
Viewed: 394 times


Visual Basic 6


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