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Polling in consoletoepassingen

Met asynchrone bewerkingen in ADO.NET kunt u tijdrovende databasebewerkingen op één thread starten terwijl u andere taken uitvoert op een andere thread. In de meeste scenario's bereikt u echter uiteindelijk een punt waar uw toepassing niet mag doorgaan totdat de databasebewerking is voltooid. In dergelijke gevallen is het handig om de asynchrone bewerking te peilen om te bepalen of de bewerking is voltooid of niet.

U kunt de IsCompleted eigenschap gebruiken om erachter te komen of de bewerking al dan niet is voltooid.

Opmerking

De volgende consoletoepassing werkt gegevens bij in de AdventureWorks-voorbeelddatabase en voert het werk asynchroon uit. Als u een langlopend proces wilt emuleren, wordt in dit voorbeeld een WAITFOR-instructie ingevoegd in de opdrachttekst. Normaal gesproken zou u niet proberen om uw opdrachten langzamer uit te voeren, maar in dit geval is het eenvoudiger om asynchroon gedrag te demonstreren.

Imports System
Imports System.Data.SqlClient

Module Module1

    Sub Main()
        ' The WAITFOR statement simply adds enough time to prove the
        ' asynchronous nature of the command.
        Dim commandText As String = _
         "UPDATE Production.Product " & _
         "SET ReorderPoint = ReorderPoint + 1 " & _
         "WHERE ReorderPoint Is Not Null;" & _
         "WAITFOR DELAY '0:0:3';" & _
         "UPDATE Production.Product " & _
         "SET ReorderPoint = ReorderPoint - 1 " & _
         "WHERE ReorderPoint Is Not Null"

        RunCommandAsynchronously(commandText, GetConnectionString())

        Console.WriteLine("Press Enter to continue.")
        Console.ReadLine()
    End Sub

    Private Sub RunCommandAsynchronously( _
     ByVal commandText As String, ByVal connectionString As String)

        ' Given command text and connection string, asynchronously
        ' execute the specified command against the connection. For
        ' this example, the code displays an indicator as it's working,
        ' verifying the asynchronous behavior.
        Using connection As New SqlConnection(connectionString)
            Try
                Dim count As Integer = 0
                Dim command As New SqlCommand(commandText, connection)
                connection.Open()
                Dim result As IAsyncResult = _
                 command.BeginExecuteNonQuery()
                While Not result.IsCompleted
                    Console.WriteLine("Waiting ({0})", count)
                    ' Wait for 1/10 second, so the counter
                    ' doesn't consume all available resources
                    ' on the main thread.
                    Threading.Thread.Sleep(100)
                    count += 1
                End While
                Console.WriteLine( _
                 "Command complete. Affected {0} rows.", _
                 command.EndExecuteNonQuery(result))
            Catch ex As SqlException
                Console.WriteLine("Error ({0}): {1}", _
                 ex.Number, ex.Message)
            Catch ex As InvalidOperationException
                Console.WriteLine("Error: {0}", ex.Message)
            Catch ex As Exception
                ' You might want to pass these errors
                ' back out to the caller.
                Console.WriteLine("Error: {0}", ex.Message)
            End Try
        End Using
    End Sub

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,
        ' you can retrieve it from a configuration file.

        ' If you have not included "Asynchronous Processing=true"
        ' in the connection string, the command will not be able
        ' to execute asynchronously.
        Return "..." & _
          "Asynchronous Processing=true"
    End Function
End Module

using System;
using System.Data;
using System.Data.SqlClient;

class Class1
{
    [STAThread]
    static void Main()
    {
        // The WAITFOR statement simply adds enough time to
        // prove the asynchronous nature of the command.

        string commandText =
          "UPDATE Production.Product SET ReorderPoint = " +
          "ReorderPoint + 1 " +
          "WHERE ReorderPoint Is Not Null;" +
          "WAITFOR DELAY '0:0:3';" +
          "UPDATE Production.Product SET ReorderPoint = " +
          "ReorderPoint - 1 " +
          "WHERE ReorderPoint Is Not Null";

        RunCommandAsynchronously(
            commandText, GetConnectionString());

        Console.WriteLine("Press Enter to continue.");
        Console.ReadLine();
    }

    private static void RunCommandAsynchronously(
      string commandText, string connectionString)
    {
        // Given command text and connection string, asynchronously
        // execute the specified command against the connection.
        // For this example, the code displays an indicator as it's
        // working, verifying the asynchronous behavior.
        using (SqlConnection connection =
          new SqlConnection(connectionString))
        {
            try
            {
                int count = 0;
                SqlCommand command =
                    new SqlCommand(commandText, connection);
                connection.Open();

                IAsyncResult result =
                    command.BeginExecuteNonQuery();
                while (!result.IsCompleted)
                {
                    Console.WriteLine(
                                    "Waiting ({0})", count++);
                    // Wait for 1/10 second, so the counter
                    // doesn't consume all available
                    // resources on the main thread.
                    System.Threading.Thread.Sleep(100);
                }
                Console.WriteLine(
                    "Command complete. Affected {0} rows.",
                command.EndExecuteNonQuery(result));
            }
            catch (SqlException ex)
            {
                Console.WriteLine("Error ({0}): {1}",
                    ex.Number, ex.Message);
            }
            catch (InvalidOperationException ex)
            {
                Console.WriteLine("Error: {0}", ex.Message);
            }
            catch (Exception ex)
            {
                // You might want to pass these errors
                // back out to the caller.
                Console.WriteLine("Error: {0}", ex.Message);
            }
        }
    }

    private static string GetConnectionString()
    {
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file.

        // If you have not included "Asynchronous Processing=true"
        // in the connection string, the command will not be able
        // to execute asynchronously.
        return "..." + "Asynchronous Processing=true";
    }
}

Zie ook

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