Can I execute code on an existing process?

Question

I have an application that runs and continuously in the system tray icon. It makes sure it is the only running instance of my application by running some code that uses a @Global mutex.

Due to 3rd party vendor limitations the only (sane) way I can integrate with one part of a vendor app is by specifying in a config file that an arbitrary command line executable is called. The parameters I care about are automatically added to the executable I specify.

So I think most people who integrated with this run a seperate program which connects to a server socket on the main program and sends a packet letting the main program know the command line has been triggered.

I'm wondering if there is a way I could do this pseudo-code..

    static void Main(string[] args)
    {
        if (isrunningcommandLine)
        {
            ConnectToAlreadyRunningProcessAndPassInfo(args); // find already running process by its process name and somehow pass the command line params
            KillProgram();
        }
        else
        {
            CheckGlobalMutexAndStart();
        }
    }

Essentially if I am running via command line connect to the already running global process and pass it some data.

I control the code that will be the client as well as the server, they are in fact the same project.

Answer 1

You can use a global named mutex to detect if your app is already running.

• If no run a server that will receive and manage the commands.
• If yes run a client and just send the commands to the server.

Then use a TCP connection on localhost to exchange messages.

    using System;
    using System.Net;
    using System.Net.Sockets;
    using System.Text;
    using System.Threading;

    namespace Test42
    {
        internal static class Program
        {
            private static int PORT = 1337;

            private static void Main()
            {
                bool ok;

                // Try to build a mutex.
                var mutex = new Mutex(true, @"Test42", out ok);

                // If build is ok, we run as a server. 
                // Otherwise, the server is already running, so we run as a client.
                if (ok)
                {
                    var server = new MyServer(PORT);
                    server.Start();
                }
                else
                {
                    var r = new Random();
                    var message = "Ho Hey : " + r.Next(50);

                    var client = new MyClient();
                    client.Send(PORT, message);
                }
            }
        }

        internal class MyClient
        {
            /// <summary>
            /// Send a message to localhost.
            /// </summary>
            /// <param name="port">The port to connect.</param>
            /// <param name="message">The message to send.</param>
            public void Send(int port, string message)
            {
                var client = new TcpClient();
                var serverEndPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), port);

                client.Connect(serverEndPoint);

                using (var stream = client.GetStream())
                {
                    var messageBuffer = Encoding.Unicode.GetBytes(message);
                    var lengthBuffer = BitConverter.GetBytes(messageBuffer.Length);

                    // Send message length.
                    stream.Write(lengthBuffer, 0, lengthBuffer.Length);

                    // Send message.
                    stream.Write(messageBuffer, 0, messageBuffer.Length);

                    stream.Flush();
                }

                client.Close();
            }
        }

        internal class MyServer
        {
            private readonly int _port;

            public MyServer(int port)
            {
                _port = port;
            }

            public void Start()
            {
                Console.WriteLine("wait for messages");
                var thread = new Thread(ThreadStart);
                thread.Start();
            }

            private void ThreadStart()
            {
                var listener = new TcpListener(IPAddress.Any, _port);
                listener.Start();
                while (true)
                {
                    var client = listener.AcceptTcpClient();
                    var clientThread = new Thread(ClientThreadStart);
                    clientThread.Start(client);
                }
            }

            private void ClientThreadStart(object obj)
            {
                var client = obj as TcpClient;
                if (client == null) return;

                using (var stream = client.GetStream())
                {
                    const int lengthLength = sizeof(int) / sizeof(byte);

                    // Read the message length.
                    var lengthBuffer = new byte[lengthLength];
                    stream.ReadAsync(lengthBuffer, 0, lengthLength).Wait();
                    var messageLength = BitConverter.ToInt32(lengthBuffer, 0);

                    // Read the message.
                    var messageBuffer = new byte[messageLength];
                    stream.ReadAsync(messageBuffer, 0, messageLength).Wait();
                    var message = Encoding.Unicode.GetString(messageBuffer);

                    Console.WriteLine("Client says: " + message);
                }

                client.Close();
            }
        }
    }