What is a good pattern for using a Global Mutex in C#?

Question

The Mutex class is very misunderstood, and Global mutexes even more so.

What is good, safe pattern to use when creating Global mutexes?

Answer 1

I really want to make sure this is out there, cause its so hard to get right.

    // unique id for global mutex - Global prefix means it is global to the machine
    const string mutex_id = "Global\\{B1E7934A-F688-417f-8FCB-65C3985E9E27}";

    static void Main(string[] args)
    {
        using (var mutex = new Mutex(false, mutex_id))
        {
            // edited by Jeremy Wiebe to add example of setting up security for multi-user usage
            var allowEveryoneRule = new MutexAccessRule("Everyone", MutexRights.FullControl, AccessControlType.Allow);
            var securitySettings = new MutexSecurity();
            securitySettings.AddAccessRule(allowEveryoneRule);
            mutex.SetAccessControl(securitySettings);

            //edited by acidzombie24
            var hasHandle = false;
            try
            {
                try
                {
                    // note, you may want to time out here instead of waiting forever
                    //edited by acidzombie24
                    //mutex.WaitOne(Timeout.Infinite, false);
                    hasHandle = mutex.WaitOne(5000, false);
                    if (hasHandle == false) return;//another instance exist
                }
                catch (AbandonedMutexException)
                {
                    // Log the fact the mutex was abandoned in another process, it will still get aquired
                }

                // Perform your work here.
            }
            finally
            {
                //edit by acidzombie24, added if statemnet
                if(hasHandle)
                    mutex.ReleaseMutex();
            }
        }
    }

Answer 2

Would this be the right way of doing the same thing with a timeout ?

// unique id for global mutex - Global prefix means it is global to the machine
const string mutex_id = "Global\\{B1E7934A-F688-417f-8FCB-65C3985E9E27}";

static void Main(string[] args)
{
    using (var mutex = new Mutex(false, mutex_id))
    {
        bool bHadMutex = false;
        try
        {
            try
            {
                // note, you may want to time out here instead of waiting forever
                bHadMutex = mutex.WaitOne(200, false);
            }
            catch (AbandonedMutexException)
            {
                // Log the fact the mutex was abandoned in another process, it will still get aquired
                bHadMutex = true;
            }

            // Perform your work here.
        }
        finally
        {
            // ReleaseMutex will throw  ApplicationException  if the calling thread does not own the mutex, so we have to check
            if (bHadMutex)
                mutex.ReleaseMutex(); // otherwise
        }
    }
}

Answer 3

This example will exit after 5 seconds if another instance is already running.

// unique id for global mutex - Global prefix means it is global to the machine
const string mutex_id = "Global\\{B1E7934A-F688-417f-8FCB-65C3985E9E27}";

static void Main(string[] args)
{

    using (var mutex = new Mutex(false, mutex_id))
    {
        try
        {
            try
            {
                if (!mutex.WaitOne(TimeSpan.FromSeconds(5), false))
                {
                    Console.WriteLine("Another instance of this program is running");
                    Environment.Exit(0);
                }
            }
            catch (AbandonedMutexException)
            {
                // Log the fact the mutex was abandoned in another process, it will still get aquired
            }

            // Perform your work here.
        }
        finally
        {
            mutex.ReleaseMutex();
        }
    }
}