Is using a Mutex to prevent multiple instances of the same program from running safe?

Question

I'm using this code to prevent a second instance of my program from running at the same time, is it safe?

Mutex appSingleton = new System.Threading.Mutex(false, "MyAppSingleInstnceMutx");
if (appSingleton.WaitOne(0, false)) {
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(new MainForm());
    appSingleton.Close();
} else {
    MessageBox.Show("Sorry, only one instance of MyApp is allowed.");
}

I'm worried that if something throws an exception and the app crashes that the Mutex will still be held. Is that true?

Answer 1

It is more usual and convenient to use Windows events for this purpose. E.g.

static EventWaitHandle s_event ;

bool created ;
s_event = new EventWaitHandle (false, 
    EventResetMode.ManualReset, "my program#startup", out created) ;
if (created) Launch () ;
else         Exit   () ;

When your process exits or terminates, Windows will close the event for you, and destroy it if no open handles remain.

Added: to manage sessions, use Local\ and Global\ prefixes for the event (or mutex) name. If your application is per-user, just append a suitably mangled logged-on user's name to the event name.