Run VBScript Consecutively - vbscript

Question

I have on Outlook rule that kicks off a batch statement which starts a VBScript that then kicks off other VBScripts based on the sender and subject heading. If two emails from the same sender come into the in box simultaneously, it will start the first instance correctly. However, the second will kick off and return an error stating "Permission denied". I would like to run each email consecutively.
I have already tried the sleep functions and other time bound delays, but the query times are not consistent due to the size of the data.
Here is the basic script I have been using.
Set olApp = CreateObject("Outlook.Application")
Set olMAPI = olApp.GetNameSpace("MAPI")
Set oFolder = olMAPI.Folders("FieldFinanceAutomatedReports#xxxxx.com").Folders("Inbox").Folders("Requested Report People")
Set allEmails = oFolder.Items
Set firstemail = allEmails.GetLast
unreadCount = 0
For Each email In oFolder.Items
If email.Unread = True Then
If email.Sender= "Sender_of_email#email.com" Then
Set objcreate = CreateObject("Scripting.FileSystemObject")
Set objread = objcreate.OpenTextFile("C:\path_to_script\script.vbs")
request = objread.ReadAll()
objread.Close
Set objread = Nothing
Execute request
Set request = Nothing
Set objcreate = Nothing
End If
WScript.Sleep 500
If email.Sender = "Another_Sender_of_email#email.com" Then
Set objcreate = CreateObject("Scripting.FileSystemObject")
Set objread = objcreate.OpenTextFile("C:\path_to_script\another_script.vbs")
another_request = objread.ReadAll()
objread.Close
Set objread = Nothing
Execute another_request
Set another_request = Nothing
Set objcreate = Nothing
End If
WScript.Sleep 500
unreadCount = unreadCount + 1
End If
Next
I would like for each of the instances to wait until it the first process is complete.

Answer 1

What you need is called a semaphore or mutex. Essentially that's a resource that can be held by only one process or thread at a time. In VBScript you could implement that by attempting to create a (temporary) file. First process to do that wins, subsequent attempts will fail because the file already exists.
Set sh = CreateObject("WScript.Shell")
Set fso = CreateObject("Scripting.FileSystemObject")
filename = sh.ExpandEnvironmentStrings("%TEMP%\mutex.txt")
'this will throw an error if the file is already opened
Set f = fso.OpenTextFile(filename, 2, True)
Note that you need to open the file for writing (second parameter set to 2). Opening it for reading (second parameter set to 1) does not suffice.
Run the operation in a loop and you can wait for another process to finish and release the mutex.
Set sh = CreateObject("WScript.Shell")
Set fso = CreateObject("Scripting.FileSystemObject")
filename = sh.ExpandEnvironmentStrings("%TEMP%\mutex.txt")
On Error Resume Next
Do
Err.Clear
Set f = fso.OpenTextFile(filename, 2, True)
If Err Then WScript.Sleep 100
Loop While Err
On Error Goto 0
Make sure you remove the file when your script leaves the critical section (or terminates), otherwise other scripts might have trouble acquiring the mutex later. A convenient way of doing this is to implement the mutex as a class. That way it will automatically be cleaned up, even if the script should terminate unexpectedly.
Class Mutex
Private f_
Private Sub Class_Initialize
Set sh = CreateObject("WScript.Shell")
Set fso = CreateObject("Scripting.FileSystemObject")
filename = sh.ExpandEnvironmentStrings("%TEMP%\mutex.txt")
On Error Resume Next
Do
Err.Clear
Set f_ = fso.OpenTextFile(filename, 2, True)
If Err Then WScript.Sleep 100
Loop While Err
On Error Goto 0
End Sub
Private Sub Class_Terminate
f_.Close
End Sub
End Class
You use that Mutex class in your code like this:
Set m = New Mutex 'acquire mutex
'...
'critical section goes here
'...
Set m = Nothing 'release mutex