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Procedimiento para especificar un programador de tareas en un bloque de flujos de datos

  • Artículo

Este documento muestra cómo asociar un programador de tareas específico al usar un flujo de datos en la aplicación. En el ejemplo, se usa la clase System.Threading.Tasks.ConcurrentExclusiveSchedulerPair en una aplicación de Windows Forms para mostrar cuándo están activas las tareas de lectura y cuándo está activa una tarea de escritura. También se usa el método TaskScheduler.FromCurrentSynchronizationContext para permitir que un bloque de flujo de datos se ejecute en el subproceso de la interfaz de usuario.

Nota

La biblioteca de flujos de datos TPL (el espacio de nombres System.Threading.Tasks.Dataflow) no se distribuye con .NET. Para instalar el espacio de nombres System.Threading.Tasks.Dataflow en Visual Studio, abra el proyecto, seleccione Administrar paquetes NuGet en el menú Proyecto y busque en línea el paquete System.Threading.Tasks.Dataflow. Como alternativa, para realizar la instalación con la CLI de .Net Core, ejecute dotnet add package System.Threading.Tasks.Dataflow.

Para crear la aplicación de Windows Forms

  1. Cree un proyecto Aplicación de Windows Forms de Visual C# o Visual Basic. En los pasos siguientes, el proyecto se denomina WriterReadersWinForms.

  2. En el diseñador de formularios del formulario principal, Form1.cs (Form1.vb para Visual Basic), agregue cuatro controles CheckBox. Establezca la propiedad Text como Lector 1 para checkBox1, Lector 2 para checkBox2, Lector 3 para checkBox3 y Escritor para checkBox4. Establezca la propiedad Enabled de cada control como False.

  3. Agregue un control Timer al formulario. Establezca la propiedad Interval en 2500.

Agregar funcionalidad de flujo de datos

En esta sección, se describe cómo crear los bloques de flujo de datos que participan en la aplicación y cómo asociar cada uno a un programador de tareas.

Para agregar funcionalidad de flujo de datos a la aplicación

  1. En el proyecto, agregue una referencia a System.Threading.Tasks.Dataflow.dll.

  2. Asegúrese de que Form1.cs (Form1.vb para Visual Basic) contenga las siguientes directivas using (Imports en Visual Basic).

    using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;
using System.Windows.Forms;

    Imports System.Threading
Imports System.Threading.Tasks
Imports System.Threading.Tasks.Dataflow

  3. Agregue un miembro de datos BroadcastBlock<T> a la clase Form1.

    // Broadcasts values to an ActionBlock<int> object that is associated
// with each check box.
BroadcastBlock<int> broadcaster = new BroadcastBlock<int>(null);

    ' Broadcasts values to an ActionBlock<int> object that is associated
' with each check box.
Private broadcaster As New BroadcastBlock(Of Integer)(Nothing)

  4. En el constructor Form1, después de llamar a InitializeComponent, cree un objeto ActionBlock<TInput> que alterne el estado de los objetos CheckBox.

    // Create an ActionBlock<CheckBox> object that toggles the state
// of CheckBox objects.
// Specifying the current synchronization context enables the
// action to run on the user-interface thread.
var toggleCheckBox = new ActionBlock<CheckBox>(checkBox =>
{
   checkBox.Checked = !checkBox.Checked;
},
new ExecutionDataflowBlockOptions
{
   TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()
});

    ' Create an ActionBlock<CheckBox> object that toggles the state
' of CheckBox objects.
' Specifying the current synchronization context enables the 
' action to run on the user-interface thread.
Dim toggleCheckBox = New ActionBlock(Of CheckBox)(Sub(checkBox) checkBox.Checked = Not checkBox.Checked, New ExecutionDataflowBlockOptions With {.TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()})

  5. En el constructor Form1, cree un objeto ConcurrentExclusiveSchedulerPair y cuatro objetos ActionBlock<TInput>, un objeto ActionBlock<TInput> para cada objeto CheckBox. Para cada objeto ActionBlock<TInput> , especifique un objeto ExecutionDataflowBlockOptions que tenga la propiedad TaskScheduler establecida en la propiedad ConcurrentScheduler para los lectores y la propiedad ExclusiveScheduler para el escritor.

    // Create a ConcurrentExclusiveSchedulerPair object.
// Readers will run on the concurrent part of the scheduler pair.
// The writer will run on the exclusive part of the scheduler pair.
var taskSchedulerPair = new ConcurrentExclusiveSchedulerPair();

// Create an ActionBlock<int> object for each reader CheckBox object.
// Each ActionBlock<int> object represents an action that can read
// from a resource in parallel to other readers.
// Specifying the concurrent part of the scheduler pair enables the
// reader to run in parallel to other actions that are managed by
// that scheduler.
var readerActions =
   from checkBox in new CheckBox[] {checkBox1, checkBox2, checkBox3}
   select new ActionBlock<int>(milliseconds =>
   {
      // Toggle the check box to the checked state.
      toggleCheckBox.Post(checkBox);

      // Perform the read action. For demonstration, suspend the current
      // thread to simulate a lengthy read operation.
      Thread.Sleep(milliseconds);

      // Toggle the check box to the unchecked state.
      toggleCheckBox.Post(checkBox);
   },
   new ExecutionDataflowBlockOptions
   {
      TaskScheduler = taskSchedulerPair.ConcurrentScheduler
   });

// Create an ActionBlock<int> object for the writer CheckBox object.
// This ActionBlock<int> object represents an action that writes to
// a resource, but cannot run in parallel to readers.
// Specifying the exclusive part of the scheduler pair enables the
// writer to run in exclusively with respect to other actions that are
// managed by the scheduler pair.
var writerAction = new ActionBlock<int>(milliseconds =>
{
   // Toggle the check box to the checked state.
   toggleCheckBox.Post(checkBox4);

   // Perform the write action. For demonstration, suspend the current
   // thread to simulate a lengthy write operation.
   Thread.Sleep(milliseconds);

   // Toggle the check box to the unchecked state.
   toggleCheckBox.Post(checkBox4);
},
new ExecutionDataflowBlockOptions
{
   TaskScheduler = taskSchedulerPair.ExclusiveScheduler
});

// Link the broadcaster to each reader and writer block.
// The BroadcastBlock<T> class propagates values that it
// receives to all connected targets.
foreach (var readerAction in readerActions)
{
   broadcaster.LinkTo(readerAction);
}
broadcaster.LinkTo(writerAction);

    ' Create a ConcurrentExclusiveSchedulerPair object.
' Readers will run on the concurrent part of the scheduler pair.
' The writer will run on the exclusive part of the scheduler pair.
Dim taskSchedulerPair = New ConcurrentExclusiveSchedulerPair()

' Create an ActionBlock<int> object for each reader CheckBox object.
' Each ActionBlock<int> object represents an action that can read 
' from a resource in parallel to other readers.
' Specifying the concurrent part of the scheduler pair enables the 
' reader to run in parallel to other actions that are managed by 
' that scheduler.
Dim readerActions = From checkBox In New CheckBox() {checkBox1, checkBox2, checkBox3} _
                    Select New ActionBlock(Of Integer)(Sub(milliseconds)
                                           ' Toggle the check box to the checked state.
                                           ' Perform the read action. For demonstration, suspend the current
                                           ' thread to simulate a lengthy read operation.
                                           ' Toggle the check box to the unchecked state.
                                           toggleCheckBox.Post(checkBox)
                                                           Thread.Sleep(milliseconds)
                                                           toggleCheckBox.Post(checkBox)
                                                       End Sub, New ExecutionDataflowBlockOptions With {.TaskScheduler = taskSchedulerPair.ConcurrentScheduler})

' Create an ActionBlock<int> object for the writer CheckBox object.
' This ActionBlock<int> object represents an action that writes to 
' a resource, but cannot run in parallel to readers.
' Specifying the exclusive part of the scheduler pair enables the 
' writer to run in exclusively with respect to other actions that are 
' managed by the scheduler pair.
Dim writerAction = New ActionBlock(Of Integer)(Sub(milliseconds)
                                                   ' Toggle the check box to the checked state.
                                                   ' Perform the write action. For demonstration, suspend the current
                                                   ' thread to simulate a lengthy write operation.
                                                   ' Toggle the check box to the unchecked state.
                                                   toggleCheckBox.Post(checkBox4)
                                                   Thread.Sleep(milliseconds)
                                                   toggleCheckBox.Post(checkBox4)
                                               End Sub, New ExecutionDataflowBlockOptions With {.TaskScheduler = taskSchedulerPair.ExclusiveScheduler})

' Link the broadcaster to each reader and writer block.
' The BroadcastBlock<T> class propagates values that it 
' receives to all connected targets.
For Each readerAction In readerActions
    broadcaster.LinkTo(readerAction)
Next readerAction
broadcaster.LinkTo(writerAction)

  6. En el constructor Form1, inicie el objeto Timer.

    // Start the timer.
timer1.Start();

    ' Start the timer.
timer1.Start()

  7. En el diseñador de formularios del formulario principal, cree un controlador de eventos para el evento Tick del temporizador.

  8. Implemente el evento Tick del temporizador.

    // Event handler for the timer.
private void timer1_Tick(object sender, EventArgs e)
{
   // Post a value to the broadcaster. The broadcaster
   // sends this message to each target.
   broadcaster.Post(1000);
}

    ' Event handler for the timer.
Private Sub timer1_Tick(ByVal sender As Object, ByVal e As EventArgs) Handles timer1.Tick
    ' Post a value to the broadcaster. The broadcaster
    ' sends this message to each target. 
    broadcaster.Post(1000)
End Sub

Dado que el bloque de flujo de datos toggleCheckBox actúa en la interfaz de usuario, es importante que esta acción se produzca en el subproceso de la interfaz de usuario. Para lograrlo, durante la construcción, este objeto proporciona un objeto ExecutionDataflowBlockOptions que tiene la propiedad TaskScheduler establecida como TaskScheduler.FromCurrentSynchronizationContext. El método FromCurrentSynchronizationContext crea un objeto TaskScheduler que funciona en el contexto de sincronización actual. Dado que al constructor Form1 se le llama desde el subproceso de la interfaz de usuario, la acción del bloque de flujo de datos toggleCheckBox se ejecuta también en el subproceso de la interfaz de usuario.

En este ejemplo, también se usa la clase ConcurrentExclusiveSchedulerPair para permitir que algunos bloques de flujo de datos actúen de forma simultánea y que otro bloque de flujo de datos actúe de forma exclusiva con respecto a todos los demás bloques de flujo de datos que se ejecutan en el mismo objeto ConcurrentExclusiveSchedulerPair. Esta técnica es útil cuando varios bloques de flujo de datos comparten un recurso y algunos requieren acceso exclusivo a ese recurso, ya que evita la necesidad de sincronizar manualmente el acceso a ese recurso. Al eliminar la sincronización manual, se puede hacer que el código sea más eficiente.

Ejemplo

En el siguiente ejemplo se muestra el código completo de Form1.cs (Form1.vb para Visual Basic).

using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;
using System.Windows.Forms;

namespace WriterReadersWinForms
{
   public partial class Form1 : Form
   {
      // Broadcasts values to an ActionBlock<int> object that is associated
      // with each check box.
      BroadcastBlock<int> broadcaster = new BroadcastBlock<int>(null);

      public Form1()
      {
         InitializeComponent();

         // Create an ActionBlock<CheckBox> object that toggles the state
         // of CheckBox objects.
         // Specifying the current synchronization context enables the
         // action to run on the user-interface thread.
         var toggleCheckBox = new ActionBlock<CheckBox>(checkBox =>
         {
            checkBox.Checked = !checkBox.Checked;
         },
         new ExecutionDataflowBlockOptions
         {
            TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()
         });

         // Create a ConcurrentExclusiveSchedulerPair object.
         // Readers will run on the concurrent part of the scheduler pair.
         // The writer will run on the exclusive part of the scheduler pair.
         var taskSchedulerPair = new ConcurrentExclusiveSchedulerPair();

         // Create an ActionBlock<int> object for each reader CheckBox object.
         // Each ActionBlock<int> object represents an action that can read
         // from a resource in parallel to other readers.
         // Specifying the concurrent part of the scheduler pair enables the
         // reader to run in parallel to other actions that are managed by
         // that scheduler.
         var readerActions =
            from checkBox in new CheckBox[] {checkBox1, checkBox2, checkBox3}
            select new ActionBlock<int>(milliseconds =>
            {
               // Toggle the check box to the checked state.
               toggleCheckBox.Post(checkBox);

               // Perform the read action. For demonstration, suspend the current
               // thread to simulate a lengthy read operation.
               Thread.Sleep(milliseconds);

               // Toggle the check box to the unchecked state.
               toggleCheckBox.Post(checkBox);
            },
            new ExecutionDataflowBlockOptions
            {
               TaskScheduler = taskSchedulerPair.ConcurrentScheduler
            });

         // Create an ActionBlock<int> object for the writer CheckBox object.
         // This ActionBlock<int> object represents an action that writes to
         // a resource, but cannot run in parallel to readers.
         // Specifying the exclusive part of the scheduler pair enables the
         // writer to run in exclusively with respect to other actions that are
         // managed by the scheduler pair.
         var writerAction = new ActionBlock<int>(milliseconds =>
         {
            // Toggle the check box to the checked state.
            toggleCheckBox.Post(checkBox4);

            // Perform the write action. For demonstration, suspend the current
            // thread to simulate a lengthy write operation.
            Thread.Sleep(milliseconds);

            // Toggle the check box to the unchecked state.
            toggleCheckBox.Post(checkBox4);
         },
         new ExecutionDataflowBlockOptions
         {
            TaskScheduler = taskSchedulerPair.ExclusiveScheduler
         });

         // Link the broadcaster to each reader and writer block.
         // The BroadcastBlock<T> class propagates values that it
         // receives to all connected targets.
         foreach (var readerAction in readerActions)
         {
            broadcaster.LinkTo(readerAction);
         }
         broadcaster.LinkTo(writerAction);

         // Start the timer.
         timer1.Start();
      }

      // Event handler for the timer.
      private void timer1_Tick(object sender, EventArgs e)
      {
         // Post a value to the broadcaster. The broadcaster
         // sends this message to each target.
         broadcaster.Post(1000);
      }
   }
}

Imports System.Threading
Imports System.Threading.Tasks
Imports System.Threading.Tasks.Dataflow


Namespace WriterReadersWinForms
    Partial Public Class Form1
        Inherits Form
        ' Broadcasts values to an ActionBlock<int> object that is associated
        ' with each check box.
        Private broadcaster As New BroadcastBlock(Of Integer)(Nothing)

        Public Sub New()
            InitializeComponent()

            ' Create an ActionBlock<CheckBox> object that toggles the state
            ' of CheckBox objects.
            ' Specifying the current synchronization context enables the 
            ' action to run on the user-interface thread.
            Dim toggleCheckBox = New ActionBlock(Of CheckBox)(Sub(checkBox) checkBox.Checked = Not checkBox.Checked, New ExecutionDataflowBlockOptions With {.TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()})

            ' Create a ConcurrentExclusiveSchedulerPair object.
            ' Readers will run on the concurrent part of the scheduler pair.
            ' The writer will run on the exclusive part of the scheduler pair.
            Dim taskSchedulerPair = New ConcurrentExclusiveSchedulerPair()

            ' Create an ActionBlock<int> object for each reader CheckBox object.
            ' Each ActionBlock<int> object represents an action that can read 
            ' from a resource in parallel to other readers.
            ' Specifying the concurrent part of the scheduler pair enables the 
            ' reader to run in parallel to other actions that are managed by 
            ' that scheduler.
            Dim readerActions = From checkBox In New CheckBox() {checkBox1, checkBox2, checkBox3} _
                                Select New ActionBlock(Of Integer)(Sub(milliseconds)
                                                       ' Toggle the check box to the checked state.
                                                       ' Perform the read action. For demonstration, suspend the current
                                                       ' thread to simulate a lengthy read operation.
                                                       ' Toggle the check box to the unchecked state.
                                                       toggleCheckBox.Post(checkBox)
                                                                       Thread.Sleep(milliseconds)
                                                                       toggleCheckBox.Post(checkBox)
                                                                   End Sub, New ExecutionDataflowBlockOptions With {.TaskScheduler = taskSchedulerPair.ConcurrentScheduler})

            ' Create an ActionBlock<int> object for the writer CheckBox object.
            ' This ActionBlock<int> object represents an action that writes to 
            ' a resource, but cannot run in parallel to readers.
            ' Specifying the exclusive part of the scheduler pair enables the 
            ' writer to run in exclusively with respect to other actions that are 
            ' managed by the scheduler pair.
            Dim writerAction = New ActionBlock(Of Integer)(Sub(milliseconds)
                                                               ' Toggle the check box to the checked state.
                                                               ' Perform the write action. For demonstration, suspend the current
                                                               ' thread to simulate a lengthy write operation.
                                                               ' Toggle the check box to the unchecked state.
                                                               toggleCheckBox.Post(checkBox4)
                                                               Thread.Sleep(milliseconds)
                                                               toggleCheckBox.Post(checkBox4)
                                                           End Sub, New ExecutionDataflowBlockOptions With {.TaskScheduler = taskSchedulerPair.ExclusiveScheduler})

            ' Link the broadcaster to each reader and writer block.
            ' The BroadcastBlock<T> class propagates values that it 
            ' receives to all connected targets.
            For Each readerAction In readerActions
                broadcaster.LinkTo(readerAction)
            Next readerAction
            broadcaster.LinkTo(writerAction)

            ' Start the timer.
            timer1.Start()
        End Sub

        ' Event handler for the timer.
        Private Sub timer1_Tick(ByVal sender As Object, ByVal e As EventArgs) Handles timer1.Tick
            ' Post a value to the broadcaster. The broadcaster
            ' sends this message to each target. 
            broadcaster.Post(1000)
        End Sub
    End Class
End Namespace

Vea también