Thursday, March 25, 2010

Call an external program with Lotusscript and wait for it to finish before continuing with your code

I occasionally need to call out to a batch file or an executable in my Lotusscript. The problem is the code has no native way of knowing when the external process has completed. Hence Execute and wait.

Using the windows API you can create a process and wait for it to complete in you lotusscript code before continuing.

an example would be where you need to run a command-line tool, with arguments, from your code. The output is a csv file that you then need to import. The size of the data is not guaranteed so you need to wait for the windows process to complete before importing.

Example code below


'this is the win32 api information

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

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 Long
hStdOutput As Long
hStdError As Long
End Type

Const STARTF_USESHOWWINDOW = &H1
Const SW_MINIMIZE = 6

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

Declare Function CloseHandle Lib "kernel32" (hObject As Long) As Boolean
Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long,ByVal dwMilliseconds As Long) As Long
Declare Function CreateProcessA Lib "kernel32" (ByVal lpApplicationName As Long,ByVal lpCommandLine As String, ByVal lpProcessAttributes As Long, ByVallpThreadAttributes As Long, ByVal bInheritHandles As Long, ByVal dwCreationFlags As Long, ByVal lpEnvironment As Long, ByVal lpCurrentDirectory As Long, lpStartupInfo As STARTUPINFO,lpProcessInformation As PROCESS_INFORMATION) As Long


Sub Initialize()

Dim cmdline As String ' this it the command you wish to run
cmdline = "application.exe -r -p -l output.csv"

Call ExecuteAndWait(cmdline)
msgbox "process finished"
end sub

' this creates the windows process and waits for it to finish before continuing on
Sub ExecuteAndWait(cmdline)
Dim NameOfProc As PROCESS_INFORMATION
Dim NameStart As STARTUPINFO
Dim X As Long
NameStart.wShowWindow = SW_MINIMIZE
NameStart.dwFlags = STARTF_USESHOWWINDOW
NameStart.cb = Len(NameStart)
X = CreateProcessA(0&, cmdline, 0&, 0&, 1&, NORMAL_PRIORITY_CLASS,0&, 0&, NameStart, NameOfProc)
X = WaitForSingleObject(NameOfProc.hProcess, INFINITE)
X = CloseHandle(NameOfProc.hProcess)
End Sub


There you have it pretty simple and straightforward. As always let me know if you have questions

4 comments:

  1. Thanks, John! I've been needing something like this for a while.

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  2. Very cool. Almost forgot this one. A mentor once said to me that if you can't build a program using windows API only, you're not a propper developer...:-)

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  3. Thanks John! Appreciate it.. Just a query, How to handle the failure or exceptions during the windows process. I have a lotus script code following and relying on this process. The lotus script code must run only if the process was successful (Eg: Backing up a file using windows process and then executing my lotus script, If backing up fails for any reason, i dont want my lotus script to run).What are the possible return values of CreateProcessA API

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