' The following example demonstrates using asynchronous methods to
' get Domain Name System information for the specified host computer.

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Collections

Namespace Examples.AdvancedProgramming.AsynchronousOperations
' Create a state object that holds each requested host name, 
' an associated IPHostEntry object or a SocketException.
    Public Class HostRequest
        ' Stores the requested host name.
        Dim hostNameValue as string
        ' Stores any SocketException returned by the Dns EndGetHostByName method.
        Dim e as SocketException
        ' Stores an IPHostEntry returned by the Dns EndGetHostByName method.
        Dim entry as IPHostEntry

        Public Sub New(name as String)
            hostNameValue = name
        End Sub
        
        ReadOnly Public Property HostName as String
            Get
                return hostNameValue
            End Get
        End Property
        
        Public Property ExceptionObject as SocketException
            Get
                return e
            End Get
            Set
                 e = value
            End Set
        End Property

        Public Property HostEntry as IPHostEntry
            Get
                return entry
            End Get
            Set
                entry = value
            End Set
        End Property
    End Class
    
    Public Class UseDelegateAndStateForAsyncCallback
        ' The number of pending requests.
        Dim Shared requestCounter as Integer
        Dim Shared hostData as ArrayList = new ArrayList()
        
        Shared Sub UpdateUserInterface()
            ' Print a message to indicate that the application
            ' is still working on the remaining requests.
            Console.WriteLine("{0} requests remaining.", requestCounter)
        End Sub
        
        Public Shared Sub Main()
            ' Create the delegate that will process the results of the 
            ' asynchronous request.
            Dim callBack as AsyncCallback = AddressOf ProcessDnsInformation
            Dim host as string
            
            Do
                Console.Write(" Enter the name of a host computer or <enter> to finish: ")
                host = Console.ReadLine()
                If host.Length > 0
                    ' Increment the request counter in a thread safe manner.
                    Interlocked.Increment (requestCounter)
                    ' Create and store the state object for this request.
                    Dim  request as HostRequest = new HostRequest(host)
                    hostData.Add(request)
                    ' Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, request)
                 End If
            Loop While host.Length > 0
            
            ' The user has entered all of the host names for lookup.
            ' Now wait until the threads complete.
            Do While requestCounter > 0
                UpdateUserInterface()
            Loop
            
            ' Display the results.
            For Each r as HostRequest In hostData
                    If IsNothing(r.ExceptionObject) = False
                        Console.WriteLine( _ 
                          "Request for host {0} returned the following error: {1}.", _
                          r.HostName, r.ExceptionObject.Message)
                    Else
                        ' Get the results.
                        Dim h as IPHostEntry = r.HostEntry
                        Dim aliases() as String = h.Aliases
                        Dim addresses() as IPAddress = h.AddressList
                        Dim j, k as Integer
                        
                        If aliases.Length > 0
                            Console.WriteLine("Aliases for {0}", r.HostName)
                            For j = 0 To aliases.Length - 1
                                Console.WriteLine("{0}", aliases(j))
                            Next j
                        End If
                        If addresses.Length > 0
                            Console.WriteLine("Addresses for {0}", r.HostName)
                            For k = 0 To addresses.Length -1
                                Console.WriteLine("{0}",addresses(k).ToString())
                            Next k
                        End If
                    End If
            Next r
       End Sub

        ' The following method is invoked when each asynchronous operation completes.
        Shared Sub ProcessDnsInformation(result as IAsyncResult)
           ' Get the state object associated with this request.
           Dim request as HostRequest= CType(result.AsyncState,HostRequest)
            Try 
                ' Get the results and store them in the state object.
                Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
                request.HostEntry = host
            Catch e as SocketException
                ' Store any SocketExceptions.
                request.ExceptionObject = e
            Finally 
                ' Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(requestCounter)
            End Try
        End Sub
    End Class
End Namespace

/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computer.
*/

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Collections;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
// Create a state object that holds each requested host name, 
// an associated IPHostEntry object or a SocketException.
    public class HostRequest
    {
        // Stores the requested host name.
        private string hostName;
        // Stores any SocketException returned by the Dns EndGetHostByName method.
        private SocketException e;
        // Stores an IPHostEntry returned by the Dns EndGetHostByName method.
        private IPHostEntry entry;

        public HostRequest(string name)
        {
            hostName = name;
        }
        
        public string HostName
        {
            get 
            {
                return hostName;
            }
        }
        
        public SocketException ExceptionObject
        {
            get 
            {
                return e;
            }
            set 
            {
                 e = value;
            }
        }

        public IPHostEntry HostEntry
        {
            get 
            {
                return entry;
            }
            set 
            {
                entry = value;
            }
        }
    }
    
    public class UseDelegateAndStateForAsyncCallback
    {
        // The number of pending requests.
        static int requestCounter;
        static ArrayList hostData = new ArrayList();
        static void UpdateUserInterface()
        {
            // Print a message to indicate that the application
            // is still working on the remaining requests.
            Console.WriteLine("{0} requests remaining.", requestCounter);
        }
        public static void Main()
        {
            // Create the delegate that will process the results of the 
            // asynchronous request.
            AsyncCallback callBack = new AsyncCallback(ProcessDnsInformation);
            string host;
            do
            {
                Console.Write(" Enter the name of a host computer or <enter> to finish: ");
                host = Console.ReadLine();
                if (host.Length > 0)
                {
                    // Increment the request counter in a thread safe manner.
                    Interlocked.Increment(ref requestCounter);
                    // Create and store the state object for this request.
                    HostRequest request = new HostRequest(host);
                    hostData.Add(request);
                    // Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, request);
                 }
            } while (host.Length > 0);
            // The user has entered all of the host names for lookup.
            // Now wait until the threads complete.
            while (requestCounter > 0)
            {
                UpdateUserInterface();
            }
            // Display the results.
            foreach(HostRequest r in hostData)
            {
                    if (r.ExceptionObject != null)
                    {
                        Console.WriteLine("Request for host {0} returned the following error: {1}.", 
                            r.HostName, r.ExceptionObject.Message);
                    }
                    else
                    {
                        // Get the results.
                        IPHostEntry h = r.HostEntry;
                        string[] aliases = h.Aliases;
                        IPAddress[] addresses = h.AddressList;
                        if (aliases.Length > 0)
                        {
                            Console.WriteLine("Aliases for {0}", r.HostName);
                            for (int j = 0; j < aliases.Length; j++)
                            {
                                Console.WriteLine("{0}", aliases[j]);
                            }
                        }
                        if (addresses.Length > 0)
                        {
                            Console.WriteLine("Addresses for {0}", r.HostName);
                            for (int k = 0; k < addresses.Length; k++)
                            {
                                Console.WriteLine("{0}",addresses[k].ToString());
                            }
                        }
                    }
            }
       }

        // The following method is invoked when each asynchronous operation completes.
        static void ProcessDnsInformation(IAsyncResult result)
        {
           // Get the state object associated with this request.
           HostRequest request = (HostRequest) result.AsyncState;
            try 
            {
                // Get the results and store them in the state object.
                IPHostEntry host = Dns.EndGetHostEntry(result);
                request.HostEntry = host;
            }
            catch (SocketException e)
            {
                // Store any SocketExceptions.
                request.ExceptionObject = e;
            }
            finally 
            {
                // Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(ref requestCounter);
            }
        }
    }
}