title: Avoid from running more than one instance
body: <p>I'm trying to set a mutex in order to allow running my application in one instance only.
  I wrote the next code (like suggested here in other post)</p>
  
  <pre><code> public partial class App : Application
      {
  
          private static string appGuid = "c0a76b5a-12ab-45c5-b9d9-d693faa6e7b9";
  
          protected override void OnStartup(StartupEventArgs e)
          {
              using (Mutex mutex = new Mutex(false, "Global\\" + appGuid))
              {
  
                  if (!mutex.WaitOne(0, false))
                  {
                      MessageBox.Show("Instance already running");
                      return;
                  }
  
                  base.OnStartup(e);
  
                 //run application code
              }
          }
  
      }
  </code></pre>
  
  <p>Regretfully this code isn't working. I can launch my application in multiple instances.
  Is anyone has an idea what is wrong in my code?
  Thanks</p>