SingleInstance.cs

using Microsoft.Win32;
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Reflection;
using System.Text;
using System.Threading;

/// <summary>
/// Application instance merger
/// Made by BahNahNah
/// </summary>
public static class SingleInstance
{
    public delegate void MergeInstanceCallback(string path, string[] args);

    private static Mutex applicationMutex = null;
    private static string InstanceKey;
    private static RegistryKey PortSave = null;
    private static Socket InstanceSocket = null;
    private static byte[] SocketBuffer;
    private static EndPoint SenderEndpoint = new IPEndPoint(IPAddress.Loopback, 0);
    private static MergeInstanceCallback MergeInstance;

    public static void Create(MergeInstanceCallback callback)
    {
        Create(callback, 1048576);
    }
    public static void Create(MergeInstanceCallback callback, int bufferSize)
    {

        if (callback == null)
            return;
        MergeInstance = callback;

        InstanceKey = Assembly.GetEntryAssembly().GetType().GUID.ToString();
        PortSave = Registry.CurrentUser.OpenSubKey(@"AppEvents\Instances", true);

        if (PortSave == null)
            PortSave = Registry.CurrentUser.CreateSubKey(@"AppEvents\Instances");

        if (InstanceKey == string.Empty)
            throw new Exception("Invalid InstanceKey");

        SocketBuffer = new byte[bufferSize];

        int instancePort = GetCurrentInstancePort();
        if (instancePort == 0)
            CreateNewInstance();
        else
            MergeInstances(instancePort);
    }
    private static void CreateNewInstance()
    {
        if (applicationMutex != null)
            applicationMutex.ReleaseMutex();

        applicationMutex = new Mutex(true, InstanceKey);

        InstanceSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        InstanceSocket.Bind(SenderEndpoint);
        PortSave.SetValue(InstanceKey, ((IPEndPoint)InstanceSocket.LocalEndPoint).Port);
        InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, ref SenderEndpoint, DataReceived, null);
    }
    private static void MergeInstances(int port)
    {
        InstanceSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

        string[] args = Environment.GetCommandLineArgs();

        using (MemoryStream ms = new MemoryStream())
        using (BinaryWriter bw = new BinaryWriter(ms))
        {
            bw.Write(args.Length);
            for (int i = 0; i < args.Length; i++)
                bw.Write(args[i]);
            InstanceSocket.SendTo(ms.ToArray(), new IPEndPoint(IPAddress.Loopback, port));
        }
        Environment.Exit(0);
    }
    private static int GetCurrentInstancePort()
    {
        try
        {
            applicationMutex = Mutex.OpenExisting(InstanceKey);
            if (PortSave == null)
                return 0;
            return (int)PortSave.GetValue(InstanceKey, 0);
        }
        catch
        {
            return 0;
        }
    }
    private static void DataReceived(IAsyncResult AR)
    {
        int bytesRead = InstanceSocket.EndReceive(AR);

        if (bytesRead == 0)
        {
            InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, ref SenderEndpoint, DataReceived, null);
            return;
        }

        byte[] data = new byte[bytesRead];
        Buffer.BlockCopy(SocketBuffer, 0, data, 0, data.Length);

        string path = string.Empty;
        string[] args = null;
        using (MemoryStream ms = new MemoryStream(data))
        using (BinaryReader br = new BinaryReader(ms))
        {
            args = new string[br.ReadInt32() - 1];
            path = br.ReadString();
            for (int i = 0; i < args.Length; i++)
                args[i] = br.ReadString();
        }
        MergeInstance(path, args);
        InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, ref SenderEndpoint, DataReceived, null);
    }
}

SingleInstance.vb

Imports System.Threading
Imports Microsoft.Win32
Imports System.Net.Sockets
Imports System.Net
Imports System.Reflection
Imports System.IO

''' <summary>
''' Application instance merger
''' Made by BahNahNah
''' 
''' Ported to VB by Tedd
''' </summary>

Public Class SingleInstance
    Public Delegate Sub MergeInstanceCallback(ByVal path As String, ByVal args As String())

    Private Shared applicationMutex As Mutex = Nothing
    Private Shared InstanceKey As String
    Private Shared PortSave As RegistryKey = Nothing
    Private Shared InstanceSocket As Socket = Nothing
    Private Shared SocketBuffer As Byte()
    Private Shared SenderEndpoint As EndPoint = New IPEndPoint(IPAddress.Loopback, 0)
    Private Shared MergeInstance As MergeInstanceCallback

    Public Shared Sub Create(ByVal callback As MergeInstanceCallback)
        Create(callback, 1048576)
    End Sub
    Public Shared Sub Create(ByVal callback As MergeInstanceCallback, ByVal bufferSize As Integer)
        If callback = Nothing Then Return

        MergeInstance = callback

        InstanceKey = Assembly.GetEntryAssembly().GetType().GUID.ToString()
        PortSave = Registry.CurrentUser.OpenSubKey("AppEvents\Instances", True)

        If PortSave Is Nothing Then PortSave = Registry.CurrentUser.CreateSubKey("AppEvents\Instances")

        If InstanceKey = Nothing Then Throw New Exception("Invalid InstanceKey")

        ReDim SocketBuffer(bufferSize)

        Dim instancePort As Integer = GetCurrentInstancePort()

        If instancePort = 0 Then
            CreateNewInstance()
        Else
            MergeInstances(instancePort)
        End If
    End Sub
    Private Shared Sub CreateNewInstance()
        If Not applicationMutex Is Nothing Then applicationMutex.ReleaseMutex()

        applicationMutex = New Mutex(True, InstanceKey)

        InstanceSocket = New Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)
        InstanceSocket.Bind(SenderEndpoint)
        PortSave.SetValue(InstanceKey, DirectCast(InstanceSocket.LocalEndPoint, IPEndPoint).Port)
        InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, SenderEndpoint, AddressOf DataReceived, Nothing)
    End Sub
    Private Shared Sub MergeInstances(ByVal port As Integer)
        InstanceSocket = New Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)

        Dim args As String() = Environment.GetCommandLineArgs()

        Using ms As MemoryStream = New MemoryStream()
            Using bw As BinaryWriter = New BinaryWriter(ms)
                bw.Write(args.Length)
                For i = 0 To args.Length - 1
                    bw.Write(args(i))
                Next
                InstanceSocket.SendTo(ms.ToArray, New IPEndPoint(IPAddress.Loopback, port))
            End Using
        End Using
        Environment.Exit(0)
    End Sub
    Private Shared Function GetCurrentInstancePort() As Integer
        Try
            applicationMutex = Mutex.OpenExisting(InstanceKey)
            If PortSave Is Nothing Then Return 0
            Return DirectCast(PortSave.GetValue(InstanceKey, 0), Integer)
        Catch
            Return 0
        End Try
    End Function
    Private Shared Sub DataReceived(ByVal AR As IAsyncResult)
        Dim bytesRead As Integer = InstanceSocket.EndReceive(AR)

        If bytesRead = 0 Then
            InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, SenderEndpoint, AddressOf DataReceived, Nothing)
            Return
        End If

        Dim data(bytesRead) As Byte
        Buffer.BlockCopy(SocketBuffer, 0, data, 0, data.Length)

        Dim path As String = Nothing
        Dim args() As String = Nothing

        Using ms As MemoryStream = New MemoryStream(data)
            Using br As BinaryReader = New BinaryReader(ms)
                ReDim args(br.ReadInt32() - 1)
                path = br.ReadString()
                For i = 0 To args.Length - 1
                    args(i) = br.ReadString
                Next
            End Using
        End Using
        MergeInstance(path, args)
        InstanceSocket.BeginReceiveFrom(SocketBuffer, 0, SocketBuffer.Length, SocketFlags.None, SenderEndpoint, AddressOf DataReceived, Nothing)
    End Sub
End Class