Procedimiento Evitar que una tarea secundaria se adjunte a su elemento primario
En este documento se explica cómo evitar que una tarea secundaria se adjunte a la tarea principal. Impedir que una tarea secundaria se adjunte a su elemento principal es útil cuando se llama a un componente que está escrito por un tercero y que también usa las tareas. Por ejemplo, un componente de terceros que utiliza la opción TaskCreationOptions.AttachedToParent para crear un objeto Task o Task<TResult> puede causar problemas en el código si es de larga duración o produce una excepción no controlada.
Ejemplo
En el ejemplo siguiente se comparan los efectos del uso de las opciones predeterminadas con los efectos de impedir que una tarea secundaria se adjunte al elemento principal. En el ejemplo se crea un objeto Task que llama a una biblioteca de terceros que también usa un objeto Task. La biblioteca de otro fabricante utiliza la opción AttachedToParent para crear el objeto Task. La aplicación utiliza la opción TaskCreationOptions.DenyChildAttach para crear la tarea principal. Esta opción indica el tiempo de ejecución para quitar la especificación AttachedToParent de las tareas secundarias.
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
// Defines functionality that is provided by a third-party.
// In a real-world scenario, this would likely be provided
// in a separate code file or assembly.
namespace Contoso
{
public class Widget
{
public Task Run()
{
// Create a long-running task that is attached to the
// parent in the task hierarchy.
return Task.Factory.StartNew(() =>
{
// Simulate a lengthy operation.
Thread.Sleep(5000);
}, TaskCreationOptions.AttachedToParent);
}
}
}
// Demonstrates how to prevent a child task from attaching to the parent.
class DenyChildAttach
{
static void RunWidget(Contoso.Widget widget,
TaskCreationOptions parentTaskOptions)
{
// Record the time required to run the parent
// and child tasks.
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Console.WriteLine("Starting widget as a background task...");
// Run the widget task in the background.
Task<Task> runWidget = Task.Factory.StartNew(() =>
{
Task widgetTask = widget.Run();
// Perform other work while the task runs...
Thread.Sleep(1000);
return widgetTask;
}, parentTaskOptions);
// Wait for the parent task to finish.
Console.WriteLine("Waiting for parent task to finish...");
runWidget.Wait();
Console.WriteLine("Parent task has finished. Elapsed time is {0} ms.",
stopwatch.ElapsedMilliseconds);
// Perform more work...
Console.WriteLine("Performing more work on the main thread...");
Thread.Sleep(2000);
Console.WriteLine("Elapsed time is {0} ms.", stopwatch.ElapsedMilliseconds);
// Wait for the child task to finish.
Console.WriteLine("Waiting for child task to finish...");
runWidget.Result.Wait();
Console.WriteLine("Child task has finished. Elapsed time is {0} ms.",
stopwatch.ElapsedMilliseconds);
}
static void Main(string[] args)
{
Contoso.Widget w = new Contoso.Widget();
// Perform the same operation two times. The first time, the operation
// is performed by using the default task creation options. The second
// time, the operation is performed by using the DenyChildAttach option
// in the parent task.
Console.WriteLine("Demonstrating parent/child tasks with default options...");
RunWidget(w, TaskCreationOptions.None);
Console.WriteLine();
Console.WriteLine("Demonstrating parent/child tasks with the DenyChildAttach option...");
RunWidget(w, TaskCreationOptions.DenyChildAttach);
}
}
/* Sample output:
Demonstrating parent/child tasks with default options...
Starting widget as a background task...
Waiting for parent task to finish...
Parent task has finished. Elapsed time is 5014 ms.
Performing more work on the main thread...
Elapsed time is 7019 ms.
Waiting for child task to finish...
Child task has finished. Elapsed time is 7019 ms.
Demonstrating parent/child tasks with the DenyChildAttach option...
Starting widget as a background task...
Waiting for parent task to finish...
Parent task has finished. Elapsed time is 1007 ms.
Performing more work on the main thread...
Elapsed time is 3015 ms.
Waiting for child task to finish...
Child task has finished. Elapsed time is 5015 ms.
*/
Imports System.Diagnostics
Imports System.Threading
Imports System.Threading.Tasks
' Defines functionality that is provided by a third-party.
' In a real-world scenario, this would likely be provided
' in a separate code file or assembly.
Namespace Contoso
Public Class Widget
Public Function Run() As Task
' Create a long-running task that is attached to the
' parent in the task hierarchy.
Return Task.Factory.StartNew(Sub() Thread.Sleep(5000), TaskCreationOptions.AttachedToParent)
' Simulate a lengthy operation.
End Function
End Class
End Namespace
' Demonstrates how to prevent a child task from attaching to the parent.
Friend Class DenyChildAttach
Private Shared Sub RunWidget(ByVal widget As Contoso.Widget, ByVal parentTaskOptions As TaskCreationOptions)
' Record the time required to run the parent
' and child tasks.
Dim stopwatch As New Stopwatch()
stopwatch.Start()
Console.WriteLine("Starting widget as a background task...")
' Run the widget task in the background.
Dim runWidget As Task(Of Task) = Task.Factory.StartNew(Function()
' Perform other work while the task runs...
Dim widgetTask As Task = widget.Run()
Thread.Sleep(1000)
Return widgetTask
End Function, parentTaskOptions)
' Wait for the parent task to finish.
Console.WriteLine("Waiting for parent task to finish...")
runWidget.Wait()
Console.WriteLine("Parent task has finished. Elapsed time is {0} ms.", stopwatch.ElapsedMilliseconds)
' Perform more work...
Console.WriteLine("Performing more work on the main thread...")
Thread.Sleep(2000)
Console.WriteLine("Elapsed time is {0} ms.", stopwatch.ElapsedMilliseconds)
' Wait for the child task to finish.
Console.WriteLine("Waiting for child task to finish...")
runWidget.Result.Wait()
Console.WriteLine("Child task has finished. Elapsed time is {0} ms.", stopwatch.ElapsedMilliseconds)
End Sub
Shared Sub Main(ByVal args() As String)
Dim w As New Contoso.Widget()
' Perform the same operation two times. The first time, the operation
' is performed by using the default task creation options. The second
' time, the operation is performed by using the DenyChildAttach option
' in the parent task.
Console.WriteLine("Demonstrating parent/child tasks with default options...")
RunWidget(w, TaskCreationOptions.None)
Console.WriteLine()
Console.WriteLine("Demonstrating parent/child tasks with the DenyChildAttach option...")
RunWidget(w, TaskCreationOptions.DenyChildAttach)
End Sub
End Class
' Sample output:
'Demonstrating parent/child tasks with default options...
'Starting widget as a background task...
'Waiting for parent task to finish...
'Parent task has finished. Elapsed time is 5014 ms.
'Performing more work on the main thread...
'Elapsed time is 7019 ms.
'Waiting for child task to finish...
'Child task has finished. Elapsed time is 7019 ms.
'
'Demonstrating parent/child tasks with the DenyChildAttach option...
'Starting widget as a background task...
'Waiting for parent task to finish...
'Parent task has finished. Elapsed time is 1007 ms.
'Performing more work on the main thread...
'Elapsed time is 3015 ms.
'Waiting for child task to finish...
'Child task has finished. Elapsed time is 5015 ms.
'
Dado que una tarea primaria no finaliza hasta que finalizan todas las tareas secundarias, una tarea secundaria que se ejecute durante mucho tiempo puede provocar que el rendimiento general de la aplicación sea bajo. En este ejemplo, cuando la aplicación usa las opciones predeterminadas para crear la tarea principal, la tarea secundaria debe finalizar antes de que finalice la principal. Cuando la aplicación utiliza la opción TaskCreationOptions.DenyChildAttach, el elemento secundario no está asociado al principal. Por lo tanto, la aplicación puede realizar un trabajo adicional después de que finalice la tarea principal y antes debe esperar a que finalice la tarea secundaria.
