VBA shell() does NOT return the exepected PID & ^Function CreateProcessA^ crashes Access

Question

I am trying to start and control processes from and started by MsAccess. For that purpose I use the shell function.

https://learn.microsoft.com/en-us/office/vba/language/reference/user-interface-help/shell-function

That function is supposed to return the PID of the started process. Since the function is quite simple there was no reason to doubt ..... Never the less I tried this morning

PID = Shell("C:\WINDOWS\NOTEPAD.EXE", 1)

stop PID is e.g. ^12345^

In windows taskmanager details , I searched notepad and I searched for a PID ^12345^

Up to my surprise:

• notepad was running with a completely different PID and
• PID ^12345^ was not present

So I decide to search for an alternative and I thought I had found that in the form of a function "Function CreateProcessA" as described here

https://learn.microsoft.com/en-us/office/vba/access/concepts/windows-api/determine-when-a-shelled-process-ends

So I did copy the code from that website and did test with

Sub TestIt()

Dim PID As Double

Call StartProcess(PID, "NotePad.exe")    'StartProcess copied below

Stop

End Sub

Tja and as expected NotePad is started. ...... AND MsAccess is crashing

So both options:

1. PID = Shell("C:\WINDOWS\NOTEPAD.EXE", 1)
2. Call StartProcess(PID, "NotePad.exe")

Are drama .......

Note that the basic info is given on the given microsoft web links, where you have to add PtrSafe to the given functions

Private Declare PtrSafe Function WaitForSingleObject Lib "kernel32"

Private Declare PtrSafe Function CreateProcessA Lib "kernel32"

Private Declare PtrSafe Function CloseHandle Lib "kernel32"

Of course it is (more than) time that those functions are replaced by 64bit versions

Sub StartProcess(ByRef PID As Double, ByVal CmdLine As String)

Dim proc As PROCESS_INFORMATION

Dim start As STARTUPINFO

Dim ReturnValue As Integer

' Initialize the STARTUPINFO structure:

start.cb = Len(start)    

'(ByVal lpApplicationName As Long,      '0&

'ByVal lpCommandLine As String,         'CmdLine$

'ByVal lpProcessAttributes As Long,     '0&

'ByVal lpThreadAttributes As Long,      '0&

'ByVal bInheritHandles As Long,         '1&

'ByVal dwCreationFlags As Long,         'NORMAL_PRIORITY_CLASS ^= &H20&^

'ByVal lpEnvironment As Long,           '0&

'ByVal lpCurrentDirectory As Long,      '0&

'lpStartupInfo As STARTUPINFO,          'start

'lpProcessInformation As PROCESS_INFORMATION    'proc

') As Long



' Start the shelled application:

ReturnValue = CreateProcessA(0&, CmdLine$, 0&, 0&, 1&, _

NORMAL_PRIORITY_CLASS, 0&, 0&, start, proc)

'PID = proc.dwProcessID

Stop

End Sub

Answer 1

I think that Shell and CreateProcess return the correct values, but some processes start other processes or instances, then exit. Therefore, you probably see the PID of intermediate processes, but the started applications still run using other processes.

To use CreateProcess, try the adjusted definitions:

Private Type STARTUPINFO
    cb As Long
    lpReserved As String
    lpDesktop As String
    lpTitle As String
    dwX As Long
    dwY As Long
    dwXSize As Long
    dwYSize As Long
    dwXCountChars As Long
    dwYCountChars As Long
    dwFillAttribute As Long
    dwFlags As Long
    wShowWindow As Integer
    cbReserved2 As Integer
    lpReserved2 As Long
    hStdInput As LongPtr
    hStdOutput As LongPtr
    hStdError As LongPtr
End Type

Private Type PROCESS_INFORMATION
    hProcess As LongPtr
    hThread As LongPtr
    dwProcessID As Long
    dwThreadID As Long
End Type

Private Declare PtrSafe Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As LongPtr, ByVal dwMilliseconds As Long) As Long

Private Declare PtrSafe Function CreateProcessA Lib "kernel32" ( _
    ByVal lpApplicationName As LongPtr, _
    ByVal lpCommandLine As String, _
    ByVal lpProcessAttributes As LongPtr, _
    ByVal lpThreadAttributes As LongPtr, _
    ByVal bInheritHandles As Long, _
    ByVal dwCreationFlags As Long, _
    ByVal lpEnvironment As LongPtr, _
    ByVal lpCurrentDirectory As LongPtr, _
    ByRef lpStartupInfo As STARTUPINFO, _
    ByRef lpProcessInformation As PROCESS_INFORMATION) As Long

Private Declare PtrSafe Function CloseHandle Lib "kernel32" (ByVal hObject As LongPtr) As Long

Private Const NORMAL_PRIORITY_CLASS = &H20&
Private Const INFINITE = -1&

Sub Test1()

    Dim proc As PROCESS_INFORMATION
    Dim start As STARTUPINFO
    Dim ReturnValue As Integer
    
    start.cb = Len(start)
    
    ReturnValue = CreateProcessA(0&, "Notepad.exe", 0&, 0&, 1&, NORMAL_PRIORITY_CLASS, 0&, 0&, start, proc)
    
    If ReturnValue = 0 Then
        MsgBox "Error"
    Else
        MsgBox proc.dwProcessID
        
        WaitForSingleObject proc.hProcess, -1
        
        MsgBox "Process exited"
        
    End If
    
End Sub

To deal with special behaviour of some applications, probably a more complex approach is required, based on "jobs". (Maybe you can start a new question with new details),