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Shell and wait for a process to finish



Shell and wait for a process to finish

One of the limitation of using the Shell function is that it is asynchronous. Below are a couple of different methods of shelling processes and waiting until they are finished (or initialised):

Option Explicit

'--------------Shell API and Constants----------
Private Const WAIT_FAILED = -1&
Private Const WAIT_OBJECT_0 = 0
Private Const WAIT_ABANDONED = &H80&
Private Const WAIT_ABANDONED_0 = &H80&
Private Const WAIT_TIMEOUT = &H102&
Private Const INFINITE = &HFFFFFFFF       '  Infinite timeout
Private Const NORMAL_PRIORITY_CLASS = &H20
Private Const SYNCHRONIZE = &H100000

Private Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)
Private Declare Function WaitForInputIdle Lib "user32" (ByVal hProcess As Long, ByVal dwMilliseconds As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long
Private Declare Function OpenProcess Lib "kernel32" (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, ByVal dwProcessId As Long) As Long

'Purpose   :    Shells a process synchronised i.e. Holds execution until application has closed.
'Inputs    :    sCommandLine        =   The Command line to run the application e.g. "Notepad.exe"
'               State               =   The Window State to run of the shelled program (A Long)
'Outputs   :    Returns the Process Handle
'Notes     :    Have noticed side effects. Other applications like Internet Explorer seem to be effected by this.

Function ShellAndHold(sCommandLine As String, Optional lState As Long = vbNormalFocus) As Long
    Dim lRetVal As Long, FileToOpen As String
    
    'Check to see that the file exists
    If FileExists(sCommandLine) Then
        'Add double quotes around the path (otherwise you can't use spaces in the path)
        If Left$(sCommandLine, 1) <> Chr(34) Then
            sCommandLine = Chr(34) & sCommandLine
        End If
        If Right$(sCommandLine, 1) <> Chr(34) Then
            sCommandLine = sCommandLine & Chr(34)
        End If
    End If
    
    'Start the shell
    lRetVal = Shell(sCommandLine, lState)
    'Open the process
    ShellAndHold = OpenProcess(SYNCHRONIZE, False, lRetVal)
    
    'Wait for the process to complete
    lRetVal = WaitForSingleObject(ShellAndHold, INFINITE)
    lRetVal = CloseHandle(ShellAndHold)
End Function


'Purpose   :    Holds execution until application has closed.
'Inputs    :    sFilePath       =   The path to the application to run e.g. "Notepad.exe"
'               [sCommandLine]  =   Any command line arguments
'               [lState]        =   The Window State to run of the shelled program (A Long)
'               [lMaxTimeOut]   =   The maximum amount of time to wait for the process to finish (in secs).
'                                   -1 = infinate
'Outputs   :    Returns the True if failed open a process or complete within the specified timeout.
'Notes     :    Similiar to ShellAndHold, but will not get any 'spiking' effects using this method.


Function ShellAndWait(sFilePath As String, Optional sCommandLine, Optional lState As VbAppWinStyle = vbNormalFocus, Optional lMaxTimeOut As Long = -1) As Boolean
    Dim lRetVal As Long, siStartTime As Single, lProcID As Long

    'Check to see that the file exists
    If FileExists(sFilePath) Then
        'Add double quotes around the path (otherwise you can't use spaces in the path)
        If Left$(sFilePath, 1) <> Chr(34) Then
            sFilePath = Chr(34) & sFilePath
        End If
        If Right$(sFilePath, 1) <> Chr(34) Then
            sFilePath = sFilePath & Chr(34)
        End If
    End If
    
    'Start the shell
    lRetVal = Shell(Trim$(sFilePath + " " + sCommandLine), lState)
    'Open the process
    lProcID = OpenProcess(SYNCHRONIZE, True, lRetVal)
    
    siStartTime = Timer
    Do
        lRetVal = WaitForSingleObject(lProcID, 0)
        If lRetVal = WAIT_OBJECT_0 Then
            'Finished process
            lRetVal = CloseHandle(lProcID)
            ShellAndWait = False
            Exit Do
        ElseIf lRetVal = WAIT_FAILED Then
            lRetVal = CloseHandle(lProcID)
            'Failed to open process
            ShellAndWait = True
            Exit Do
        End If
        Sleep 100
        If lMaxTimeOut > 0 Then
            'Check timeout has not been exceeded
            If siStartTime + lMaxTimeOut < Timer Then
                'Failed, timeout exceeded
                lRetVal = CloseHandle(lProcID)
                ShellAndWait = True
            End If
        End If
    Loop
End Function


'Purpose   :    Holds execution until application has finished opening
'Inputs    :    sCommandLine     =   The Command line to run the application e.g. "Notepad.exe"
'               lState           =   The Window State to run of the shelled program (A Long)
'Outputs   :    Returns the Process Handle
'Notes     :    Use this when you want to wait for an application to finishing opening before proceeding
'               The side effects mentioned in ShellAndHold will be negligible since the most applications
'               load in under 5 seconds.


Function ShellAndWaitReady(sCommandLine As String, Optional lState As Long = vbNormalFocus) As Long
    Dim lhProc As Long
    
    If Left$(sCommandLine, 1) <> Chr(34) Then
        sCommandLine = Chr(34) & sCommandLine
    End If
    If Right$(sCommandLine, 1) <> Chr(34) Then
        sCommandLine = sCommandLine & Chr(34)
    End If
    lhProc = Shell(sCommandLine, lState)
    'Wait for the process to initialize
    Call WaitForInputIdle(lhProc, INFINITE)
    'Return the handle
    ShellAndWaitReady = lhProc
End Function


'Purpose     :  Checks if a file exists
'Inputs      :  sFilePathName                   The path and file name e.g. "C:\Autoexec.bat"
'Outputs     :  Returns True if the file exists


Function FileExists(sFilePathName As String) As Boolean
    
    On Error GoTo ErrFailed
    If Len(sFilePathName) Then
        If (GetAttr(sFilePathName) And vbDirectory) < 1 Then
            'File Exists
            FileExists = True
        End If
    End If
    Exit Function
    
ErrFailed:
    'File Exists
    FileExists = False
    On Error GoTo 0
End Function

'Purpose     :  Converts a File Name and Path to a Path
'Inputs      :  sFilePathName                   The path and file name e.g. "C:\Autoexec.bat"
'Outputs     :  Returns the path


Function PathFileToPath(sFilePathName As String) As String
    Dim ThisChar As Long

    For ThisChar = 0 To Len(sFilePathName) - 1
        If Mid$(sFilePathName, Len(sFilePathName) - ThisChar, 1) = "\" Then
            PathFileToPath = Left$(sFilePathName, Len(sFilePathName) - ThisChar)
            Exit For
        End If
    Next
End Function