How do I test if another installation is already in progress?

See the description of the _MSIExecute Mutex on MSDN.

I was getting an unhandled exception using the code above. I cross referenced this article witt this one

Here's my updated code:

  /// <summary>
/// Wait (up to a timeout) for the MSI installer service to become free.
/// </summary>
/// <returns>
/// Returns true for a successful wait, when the installer service has become free.
/// Returns false when waiting for the installer service has exceeded the timeout.
/// </returns>
public static bool IsMsiExecFree(TimeSpan maxWaitTime)
{
    // The _MSIExecute mutex is used by the MSI installer service to serialize installations
    // and prevent multiple MSI based installations happening at the same time.
    // For more info: http://msdn.microsoft.com/en-us/library/aa372909(VS.85).aspx
    const string installerServiceMutexName = "Global\\_MSIExecute";
    Mutex MSIExecuteMutex = null;
    var isMsiExecFree = false;
    try
    {
            MSIExecuteMutex = Mutex.OpenExisting(installerServiceMutexName,
                            System.Security.AccessControl.MutexRights.Synchronize);
            isMsiExecFree = MSIExecuteMutex.WaitOne(maxWaitTime, false);
    }
        catch (WaitHandleCannotBeOpenedException)
        {
            // Mutex doesn't exist, do nothing
            isMsiExecFree = true;
        }
        catch (ObjectDisposedException)
        {
            // Mutex was disposed between opening it and attempting to wait on it, do nothing
            isMsiExecFree = true;
        }
        finally
        {
            if(MSIExecuteMutex != null && isMsiExecFree)
            MSIExecuteMutex.ReleaseMutex();
        }
    return isMsiExecFree;

}

Sorry for hijacking you post!

I have been working on this - for about a week - using your notes (Thank you) and that from other sites - too many to name (Thank you all).

I stumbled across information revealing that the Service could yield enough information to determine if the MSIEXEC service is already in use. The Service being 'msiserver' - Windows Installer - and it's information being both state and acceptstop.

The following VBScript code checks this.

Set objWMIService = GetObject("winmgmts:\\.\root\cimv2")
Check = False
Do While Not Check
   WScript.Sleep 3000
   Set colServices = objWMIService.ExecQuery("Select * From Win32_Service Where Name="'msiserver'")
   For Each objService In colServices
      If (objService.Started And Not objService.AcceptStop)  
         WScript.Echo "Another .MSI is running."
      ElseIf ((objService.Started And objService.AcceptStop) Or Not objService.Started) Then
         WScript.Echo "Ready to install an .MSI application."
         Check = True
      End If
   Next
Loop