Ensure That Only One Instance of an Application Can Execute Concurrently

The Mutex provides a mechanism for synchronizing the execution of threads across process boundaries and in addition provides a convenient mechanism through which to ensure that only a single instance of an application is running concurrently. By trying to acquire ownership of a named Mutex at startup and exiting if the Mutex can't be acquired, you can ensure that only one instance of your application is running. This example uses a Mutex named MutexExample to ensure that only a single instance of the example can execute.

using System;
using System.Threading;

public class MutexExample {

    public static void Main() {

        // A boolean that indicates whether this application has
        // initial ownership of the Mutex.
        bool ownsMutex;

        // Attempt to create and take ownership of a Mutex named
        // MutexExample.
        using (Mutex mutex = 
                   new Mutex(true, "MutexExample", out ownsMutex)) {

            // If the application owns the Mutex it can continue to execute;
            // otherwise, the application should exit. 
            if (ownsMutex) {

                Console.WriteLine("This application currently owns the" +
                    " mutex named MutexExample. Additional instances of" +
                    " this application will not run until you release" +
                    " the mutex by pressing Enter.");

                Console.ReadLine();

                // Release the mutex
                mutex.ReleaseMutex();

            } else {

                Console.WriteLine("Another instance of this application " +
                    " already owns the mutex named MutexExample. This" +
                    " instance of the application will terminate.");
            }
        }

        // Wait to continue.
        Console.WriteLine("Main method complete. Press Enter.");
        Console.ReadLine();
    }
}