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Выполнение опросов в консольных приложениях

Асинхронные операции в ADO.NET позволяют инициировать длительные операции с базами данных в одном потоке, одновременно выполняя другие задачи в другом. Однако в большинстве сценариев, в конечном счете, вы достигнете точки, при которой вам нужно будет остановить работу приложения до завершения операции с базой данных. В таких случаях полезно выполнить опрос асинхронной операции, чтобы определить, завершена ли операция.

Чтобы узнать, завершилась ли операция, можно использовать свойство IsCompleted.

Пример

В следующем приложении командной строки происходит асинхронное обновление данных в образце базы данных AdventureWorks. Чтобы эмулировать длительный процесс, в этом примере в текст команды вставляется инструкция WAITFOR. Обычно вам не нужно пытаться сделать выполнение команд медленнее, но в этом случае это упрощает демонстрацию асинхронного поведения.

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";
    }
}

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