PowerToys/src/modules/poweraccent/PowerAccent.UI/App.xaml.cs

// Copyright (c) Microsoft Corporation
// The Microsoft Corporation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Threading;
using System.Windows;

namespace PowerAccent.UI
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        private static Mutex _mutex;

        protected override void OnStartup(StartupEventArgs e)
        {
            const string appName = "QuickAccent";
            bool createdNew;

            _mutex = new Mutex(true, appName, out createdNew);

            if (!createdNew)
            {
                // app is already running! Exiting the application
                Application.Current.Shutdown();
            }

            base.OnStartup(e);
        }
    }
}