使用 AsyncWaitHandle 封鎖應用程式執行
更新：2007 年 11 月
無法在等候非同步作業 (Asynchronous Operation) 結果時繼續進行其他工作的應用程式，就必須在作業完成之前維持封鎖。請使用下列其中一個選項，在等候非同步作業完成時，封鎖您應用程式的主執行緒：
使用非同步作業的 BeginOperationName 方法所傳回之 IAsyncResult 的 AsyncWaitHandle 屬性。此主題中會示範這個方法。
呼叫非同步作業的 EndOperationName 方法。如需進行這個方法的範例，請參閱以結束非同步作業的方式封鎖應用程式執行。
在非同步作業完成之前，使用一或多個 WaitHandle 物件來封鎖的應用程式，通常都會呼叫 BeginOperationName 方法，來執行不需要作業結果即可完成的工作，然後在非同步作業完成之前維持封鎖。只要使用 AsyncWaitHandle 呼叫其中一個 WaitOne 方法，應用程式即可封鎖單一作業。若要在等候一組非同步作業完成的同時封鎖，請將關聯的 AsyncWaitHandle 物件儲存到陣列中，並呼叫其中一個 WaitAll 方法。若要在等候任何一組非同步作業完成的同時封鎖，請將關聯的 AsyncWaitHandle 物件儲存到陣例中，並呼叫其中一個 WaitAny 方法。
範例
下列程式碼範例會示範在 DNS 類別中使用非同步方法，以擷取使用者所指定之電腦的網域名稱系統資訊。且會示範使用與非同步作業關聯的 WaitHandle 來進行封鎖。請注意，由於在使用此處理方法時不需要 BeginGetHostByNamerequestCallback 和 stateObject 參數，對於這兩個參數都會傳遞 null (Visual Basic 中的 Nothing)。
' 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
namespace Examples.AdvancedProgramming.AsynchronousOperations
Public Class WaitUntilOperationCompletes
Public Shared Sub Main(args() as String)
' Make sure the caller supplied a host name.
If(args.Length = 0)
' Print a message and exit.
Console.WriteLine("You must specify the name of a host computer.")
End
End If
' Start the asynchronous request for DNS information.
Dim result as IAsyncResult= Dns.BeginGetHostEntry(args(0), Nothing, Nothing)
Console.WriteLine("Processing request for information...")
' Wait until the operation completes.
result.AsyncWaitHandle.WaitOne()
' The operation completed. Process the results.
Try
' Get the results.
Dim host as IPHostEntry = Dns.EndGetHostEntry(result)
Dim aliases() as String = host.Aliases
Dim addresses() as IPAddress= host.AddressList
Dim i as Integer
If aliases.Length > 0
Console.WriteLine("Aliases")
For i = 0 To aliases.Length -1
Console.WriteLine("{0}", aliases(i))
Next i
End If
If addresses.Length > 0
Console.WriteLine("Addresses")
For i = 0 To addresses.Length -1
Console.WriteLine("{0}", addresses(i).ToString())
Next i
End If
Catch e as SocketException
Console.WriteLine("An exception occurred while processing the request: {0}" _
, e.Message)
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;
namespace Examples.AdvancedProgramming.AsynchronousOperations
{
public class WaitUntilOperationCompletes
{
public static void Main(string[] args)
{
// Make sure the caller supplied a host name.
if (args.Length == 0 || args[0].Length == 0)
{
// Print a message and exit.
Console.WriteLine("You must specify the name of a host computer.");
return;
}
// Start the asynchronous request for DNS information.
IAsyncResult result = Dns.BeginGetHostEntry(args[0], null, null);
Console.WriteLine("Processing request for information...");
// Wait until the operation completes.
result.AsyncWaitHandle.WaitOne();
// The operation completed. Process the results.
try
{
// Get the results.
IPHostEntry host = Dns.EndGetHostEntry(result);
string[] aliases = host.Aliases;
IPAddress[] addresses = host.AddressList;
if (aliases.Length > 0)
{
Console.WriteLine("Aliases");
for (int i = 0; i < aliases.Length; i++)
{
Console.WriteLine("{0}", aliases[i]);
}
}
if (addresses.Length > 0)
{
Console.WriteLine("Addresses");
for (int i = 0; i < addresses.Length; i++)
{
Console.WriteLine("{0}",addresses[i].ToString());
}
}
}
catch (SocketException e)
{
Console.WriteLine("Exception occurred while processing the request: {0}",
e.Message);
}
}
}
}