Question

My app is forced to use a 3rd party module which will blue-screen Windows if two instances are started at the same time on the same machine. To work around the issue, my C# app has a mutex:

static Mutex mutex = new Mutex(true, "{MyApp_b9d19f99-b83e-4755-9b11-d204dbd6d096}");  

And I check if it’s present – and if so I show an error message and close the app:

bool IsAnotherInstanceRunning()
{
    if (mutex.WaitOne(TimeSpan.Zero, true))
        return (true);
    else
        return (false);
}

The problem is if two users can log in and open the application at the same time, and IsAnotherInstanceRunning() will return false.

How do I get around this?

Answer 1

Prefix the name of the mutex with “Global\”.

static Mutex mutex = new Mutex(true, "Global\MyApp_b9d19f99-b83e-4755-9b11-d204dbd6d096");  

From http://msdn.microsoft.com/en-us/library/system.threading.mutex.aspx:

If its name begins with the prefix
“Global\”, the mutex is visible in all
terminal server sessions. If its name
begins with the prefix “Local\”, the
mutex is visible only in the terminal
server session where it was created.
In that case, a separate mutex with
the same name can exist in each of the
other terminal server sessions on the
server. If you do not specify a prefix
when you create a named mutex, it
takes the prefix “Local\”.