Source code in the csharp programming language

using System;
using System.Net;
using System.Net.Sockets;

class Program {        
    static void Main(string[] args) {        
        try {
            TcpListener server = new TcpListener(IPAddress.Any, 12345);
            server.Start();
        } 
       
        catch (SocketException e) {
            if (e.SocketErrorCode == SocketError.AddressAlreadyInUse) {
                Console.Error.WriteLine("Already running.");
            }
        }
    }
}


// Use this class in your process to guard against multiple instances
//
// This is valid for C# running on Windows, but not for C# with Linux.
//
using System;
using System.Threading;

/// <summary>
/// RunOnce should be instantiated in the calling processes main clause
/// (preferably using a "using" clause) and then calling process
/// should then check AlreadyRunning and do whatever is appropriate
/// </summary>
public class RunOnce : IDisposable
{
	public RunOnce( string name )
	{
		m_name = name;
		AlreadyRunning = false;

		bool created_new = false;

		m_mutex = new Mutex( false, m_name, out created_new );

		AlreadyRunning = !created_new;
	}

	~RunOnce()
	{
		DisposeImpl( false );
	}

	public bool AlreadyRunning
	{
		get { return m_already_running; }
		private set { m_already_running = value; }
	}

	private void DisposeImpl( bool is_disposing )
	{
		GC.SuppressFinalize( this );

		if( is_disposing )
		{
			m_mutex.Close();
		}
	}

	#region IDisposable Members

	public void Dispose()
	{
		DisposeImpl( true );
	}

	#endregion

	private string m_name;
	private bool m_already_running;
	private Mutex m_mutex;
}

class Program
{
    // Example code to use this
    static void Main( string[] args )
    {
        using ( RunOnce ro = new RunOnce( "App Name" ) )
        {
            if ( ro.AlreadyRunning )
            {
                Console.WriteLine( "Already running" );
                return;
            }

            // Program logic
        }
    }
}