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

Question

Assuming I'm trying to automate the installation of something on windows and I want to try to test whether another installation is in progress before attempting install. I don't have control over the installer and have to do this in the automation framework. Is there a better way to do this, some win32 api?, than just testing if msiexec is running?

[Update 2]

Improved the previous code I had been using to just access the mutex directly, this is a lot more reliable:

using System.Threading;

[...]

/// <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 WaitForInstallerServiceToBeFree(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";

    try
    {
        Mutex MSIExecuteMutex = Mutex.OpenExisting(installerServiceMutexName, 
            System.Security.AccessControl.MutexRights.Synchronize);
        bool waitSuccess = MSIExecuteMutex.WaitOne(maxWaitTime, false);
        MSIExecuteMutex.ReleaseMutex();
        return waitSuccess;
    }
    catch (WaitHandleCannotBeOpenedException)
    {
        // Mutex doesn't exist, do nothing
    }
    catch (ObjectDisposedException)
    {
        // Mutex was disposed between opening it and attempting to wait on it, do nothing
    }
    return true;
}

Answer 1

See the description of the _MSIExecute Mutex on MSDN.