AsyncCallback デリゲートの使用による非同期操作の終了

[アーティクル]
04/07/2023

非同期操作の結果の待機中に、他の作業を実行できるアプリケーションは、操作が完了するまで待機をブロックする必要はありません。次のオプションのいずれかを使用して、非同期操作が完了するまでの待機中に、手順の実行を継続します。

AsyncCallback デリゲートを使用し、個別のスレッドで非同期操作の結果を処理します。このトピックでは、この方法のデモが実行されます。
非同期操作の BeginOperationName メソッドによって返される IAsyncResult の IsCompleted プロパティを使用して、その操作が完了したかどうかを判断します。この方法のデモを実行する例については、「非同期操作のステータスのポーリング」を参照してください。

例

次のコード例は、ユーザー指定のコンピューターのドメインネームシステム (DNS) 情報を取得するために、Dns クラスの非同期メソッドを使用してデモを実行します。この例では、ProcessDnsInformation メソッドを参照する AsyncCallback デリゲートを作成します。このメソッドは、DNS 情報に対する非同期要求ごとに 1 回呼び出されます。

ユーザー指定のホストは、BeginGetHostByName Object パラメーターに渡されます。複雑な状態オブジェクトの定義と使用に関するデモを実行する例については、「AsyncCallback デリゲートおよび状態オブジェクトの使用」を参照してください。

/*
The following example demonstrates using asynchronous methods to
get Domain Name System information for the specified host computers.
This example uses a delegate to obtain the results of each asynchronous
operation.
*/

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

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class UseDelegateForAsyncCallback
    {
        static int requestCounter;
        static ArrayList hostData = new ArrayList();
        static StringCollection hostNames = new StringCollection();
        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);
                    // Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, host);
                 }
            } 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.
            for (int i = 0; i< hostNames.Count; i++)
            {
                object data = hostData [i];
                string message = data as string;
                // A SocketException was thrown.
                if (message != null)
                {
                    Console.WriteLine("Request for {0} returned message: {1}",
                        hostNames[i], message);
                    continue;
                }
                // Get the results.
                IPHostEntry h = (IPHostEntry) data;
                string[] aliases = h.Aliases;
                IPAddress[] addresses = h.AddressList;
                if (aliases.Length > 0)
                {
                    Console.WriteLine("Aliases for {0}", hostNames[i]);
                    for (int j = 0; j < aliases.Length; j++)
                    {
                        Console.WriteLine("{0}", aliases[j]);
                    }
                }
                if (addresses.Length > 0)
                {
                    Console.WriteLine("Addresses for {0}", hostNames[i]);
                    for (int k = 0; k < addresses.Length; k++)
                    {
                        Console.WriteLine("{0}",addresses[k].ToString());
                    }
                }
            }
       }

        // The following method is called when each asynchronous operation completes.
        static void ProcessDnsInformation(IAsyncResult result)
        {
            string hostName = (string) result.AsyncState;
            hostNames.Add(hostName);
            try
            {
                // Get the results.
                IPHostEntry host = Dns.EndGetHostEntry(result);
                hostData.Add(host);
            }
            // Store the exception message.
            catch (SocketException e)
            {
                hostData.Add(e.Message);
            }
            finally
            {
                // Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(ref requestCounter);
            }
        }
    }
}


'The following example demonstrates using asynchronous methods to
'get Domain Name System information for the specified host computers.
'This example uses a delegate to obtain the results of each asynchronous 
'operation.

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

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class UseDelegateForAsyncCallback

        Dim Shared requestCounter as Integer
        Dim Shared hostData as ArrayList = new ArrayList()
        Dim Shared hostNames as StringCollection = new StringCollection()
        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
            Dim host as string
            Dim i, j, k as Integer
            callback = AddressOf ProcessDnsInformation
            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)
                    ' Start the asynchronous request for DNS information.
                    Dns.BeginGetHostEntry(host, callBack, host)
                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 i = 0 To hostNames.Count - 1
                Dim dataObject as Object = hostData(i)
                Dim message as String

                ' Was a SocketException was thrown?
                If TypeOf dataObject is String
                    message = CType(dataObject, String)
                    Console.WriteLine("Request for {0} returned message: {1}", _
                        hostNames(i), message)
                Else
                    ' Get the results.
                    Dim h as IPHostEntry = CType(dataObject, IPHostEntry)
                    Dim aliases() as String = h.Aliases
                    Dim addresses() as IPAddress = h.AddressList
                    If aliases.Length > 0
                        Console.WriteLine("Aliases for 0}", hostNames(i))
                        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}", hostNames(i))
                        For k = 0 To addresses.Length - 1
                            Console.WriteLine("{0}", addresses(k).ToString())
                        Next k
                    End If
                End If
            Next i
        End Sub

        ' The following method is called when each asynchronous operation completes.
        Shared Sub ProcessDnsInformation(result as IAsyncResult)

            Dim hostName as String = CType(result.AsyncState, String)
            hostNames.Add(hostName)
            Try
                ' Get the results.
                Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
                hostData.Add(host)
                ' Store the exception message.
            Catch e as SocketException
                hostData.Add(e.Message)
            Finally
                ' Decrement the request counter in a thread-safe manner.
                Interlocked.Decrement(requestCounter)
            End Try
        End Sub
    End Class
End Namespace

AsyncCallback デリゲートの使用による非同期操作の終了

例

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