Flow.Launcher/Flow.Launcher/Helper/SingleInstance.cs

using System;
using System.IO.Pipes;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;

// http://blogs.microsoft.co.il/arik/2010/05/28/wpf-single-instance-application/
// modified to allow single instace restart
namespace Flow.Launcher.Helper
{
    public interface ISingleInstanceApp 
    { 
         void OnSecondAppStarted(); 
    } 

    /// <summary>
    /// This class checks to make sure that only one instance of 
    /// this application is running at a time.
    /// </summary>
    /// <remarks>
    /// Note: this class should be used with some caution, because it does no
    /// security checking. For example, if one instance of an app that uses this class
    /// is running as Administrator, any other instance, even if it is not
    /// running as Administrator, can activate it with command line arguments.
    /// For most apps, this will not be much of an issue.
    /// </remarks>
    public static class SingleInstance<TApplication>  
                where   TApplication: Application ,  ISingleInstanceApp 
                                    
    {
        #region Private Fields

        /// <summary>
        /// String delimiter used in channel names.
        /// </summary>
        private const string Delimiter = ":";

        /// <summary>
        /// Suffix to the channel name.
        /// </summary>
        private const string ChannelNameSuffix = "SingeInstanceIPCChannel";

        /// <summary>
        /// Application mutex.
        /// </summary>
        internal static Mutex singleInstanceMutex;

        #endregion

        #region Public Methods

        /// <summary>
        /// Checks if the instance of the application attempting to start is the first instance. 
        /// If not, activates the first instance.
        /// </summary>
        /// <returns>True if this is the first instance of the application.</returns>
        public static bool InitializeAsFirstInstance( string uniqueName )
        {
            // Build unique application Id and the IPC channel name.
            string applicationIdentifier = uniqueName + Environment.UserName;

            string channelName = String.Concat(applicationIdentifier, Delimiter, ChannelNameSuffix);

            // Create mutex based on unique application Id to check if this is the first instance of the application. 
            bool firstInstance;
            singleInstanceMutex = new Mutex(true, applicationIdentifier, out firstInstance);
            if (firstInstance)
            {
                _ = CreateRemoteService(channelName);
                return true;
            }
            else
            {
                _ = SignalFirstInstance(channelName);
                return false;
            }
        }

        /// <summary>
        /// Cleans up single-instance code, clearing shared resources, mutexes, etc.
        /// </summary>
        public static void Cleanup()
        {
            singleInstanceMutex?.ReleaseMutex();
        }

        #endregion

        #region Private Methods

        /// <summary>
        /// Creates a remote server pipe for communication. 
        /// Once receives signal from client, will activate first instance.
        /// </summary>
        /// <param name="channelName">Application's IPC channel name.</param>
        private static async Task CreateRemoteService(string channelName)
        {
            using (NamedPipeServerStream pipeServer = new NamedPipeServerStream(channelName, PipeDirection.In))
            {
                while(true)
                {
                    // Wait for connection to the pipe
                    await pipeServer.WaitForConnectionAsync();
                    if (Application.Current != null)
                    {
                        // Do an asynchronous call to ActivateFirstInstance function
                        Application.Current.Dispatcher.Invoke(ActivateFirstInstance);
                    }
                    // Disconect client
                    pipeServer.Disconnect();
                }
            }
        }

        /// <summary>
        /// Creates a client pipe and sends a signal to server to launch first instance
        /// </summary>
        /// <param name="channelName">Application's IPC channel name.</param>
        /// <param name="args">
        /// Command line arguments for the second instance, passed to the first instance to take appropriate action.
        /// </param>
        private static async Task SignalFirstInstance(string channelName)
        {
            // Create a client pipe connected to server
            using (NamedPipeClientStream pipeClient = new NamedPipeClientStream(".", channelName, PipeDirection.Out))
            {
                // Connect to the available pipe
                await pipeClient.ConnectAsync(0);
            }
        }

        /// <summary>
        /// Callback for activating first instance of the application.
        /// </summary>
        /// <param name="arg">Callback argument.</param>
        /// <returns>Always null.</returns>
        private static object ActivateFirstInstanceCallback(object o)
        {
            ActivateFirstInstance();
            return null;
        }

        /// <summary>
        /// Activates the first instance of the application with arguments from a second instance.
        /// </summary>
        /// <param name="args">List of arguments to supply the first instance of the application.</param>
        private static void ActivateFirstInstance()
        {
            // Set main window state and process command line args
            if (Application.Current == null)
            {
                return;
            }

            ((TApplication)Application.Current).OnSecondAppStarted();
        }

        #endregion
    }
}