TimerApp/SingleInstanceManager.cs

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

namespace TimerApp
{
    internal sealed class SingleInstanceManager : IDisposable
    {
        private const string MutexName = "Local\\TimerApp.SingleInstance";
        private const string PipeName = "TimerApp.SingleInstancePipe";

        private readonly Mutex _mutex;
        private readonly CancellationTokenSource _cts = new();

        private SingleInstanceManager(Mutex mutex)
        {
            _mutex = mutex;
        }

        public static bool TryAcquire(out SingleInstanceManager? manager)
        {
            manager = null;

            try
            {
                var mutex = new Mutex(true, MutexName, out bool createdNew);
                if (!createdNew)
                {
                    mutex.Dispose();
                    return false;
                }

                manager = new SingleInstanceManager(mutex);
                return true;
            }
            catch
            {
                return true;
            }
        }

        public static void SignalExistingInstance()
        {
            try
            {
                using var client = new NamedPipeClientStream(".", PipeName, PipeDirection.Out);
                client.Connect(200);
                using var writer = new StreamWriter(client) { AutoFlush = true };
                writer.WriteLine("show");
            }
            catch
            {
            }
        }

        public void StartServer(Action onShowRequested)
        {
            Task.Run(() => ServerLoop(onShowRequested, _cts.Token));
        }

        private static async Task ServerLoop(Action onShowRequested, CancellationToken cancellationToken)
        {
            while (!cancellationToken.IsCancellationRequested)
            {
                try
                {
                    using var server = new NamedPipeServerStream(
                        PipeName,
                        PipeDirection.In,
                        1,
                        PipeTransmissionMode.Byte,
                        PipeOptions.Asynchronous
                    );

                    await server.WaitForConnectionAsync(cancellationToken).ConfigureAwait(false);

                    using var reader = new StreamReader(server);
                    string? line = await reader.ReadLineAsync(cancellationToken).ConfigureAwait(false);
                    if (string.Equals(line, "show", StringComparison.OrdinalIgnoreCase))
                        onShowRequested();
                }
                catch (OperationCanceledException)
                {
                    return;
                }
                catch
                {
                    await Task.Delay(150, cancellationToken).ConfigureAwait(false);
                }
            }
        }

        public void Dispose()
        {
            try
            {
                _cts.Cancel();
            }
            catch
            {
            }

            try
            {
                _mutex.ReleaseMutex();
            }
            catch
            {
            }

            _mutex.Dispose();
            _cts.Dispose();
        }
    }
}