Практическое руководство. Запрет присоединения дочерней задачи к ее родительской задачеHow to: Prevent a Child Task from Attaching to its Parent

В этом документе показано, как предотвратить прикрепление дочерней задачи к родительской.This document demonstrates how to prevent a child task from attaching to the parent task. Предотвращение прикрепления дочерней задачи к родительской полезно при вызове компонента, написанного сторонним разработчиком и также использующим задачи.Preventing a child task from attaching to its parent is useful when you call a component that is written by a third party and that also uses tasks. Например, компонент стороннего разработчика, использующий параметр TaskCreationOptions.AttachedToParent для создания объекта Task или Task<TResult>, может вызвать проблемы в коде, если он продолжительный или создает необрабатываемое исключение.For example, a third-party component that uses the TaskCreationOptions.AttachedToParent option to create a Task or Task<TResult> object can cause problems in your code if it is long-running or throws an unhandled exception.

ПримерExample

В следующем примере сравниваются последствия использования параметров по умолчанию с последствиями предотвращения прикрепления дочерней задачи к родительской.The following example compares the effects of using the default options to the effects of preventing a child task from attaching to the parent. В примере создается объект Task, вызывающий библиотеку стороннего разработчика, которая также использует объект Task.The example creates a Task object that calls into a third-party library that also uses a Task object. Библиотека стороннего разработчика использует параметр AttachedToParent для создания объекта Task.The third-party library uses the AttachedToParent option to create the Task object. Приложение использует параметр TaskCreationOptions.DenyChildAttach для создания родительской задачи.The application uses the TaskCreationOptions.DenyChildAttach option to create the parent task. Этот параметр выдает среде выполнения указание удалить спецификацию AttachedToParent в дочерних задачах.This option instructs the runtime to remove the AttachedToParent specification in child tasks.

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.
'

Поскольку родительская задача не завершается, пока не завершатся все дочерние задачи, длительная дочерняя задача может привести к ухудшению производительности приложения в целом.Because a parent task does not finish until all child tasks finish, a long-running child task can cause the overall application to perform poorly. В этом примере, когда приложение использует параметры по умолчанию для создания родительской задачи, дочерняя задача должна выполниться до завершения родительской задачи.In this example, when the application uses the default options to create the parent task, the child task must finish before the parent task finishes. Если приложение использует параметр TaskCreationOptions.DenyChildAttach, дочерняя задача не будет прикреплена к родительской.When the application uses the TaskCreationOptions.DenyChildAttach option, the child is not attached to the parent. Поэтому приложение может выполнять дополнительную работу после завершения родительской задачи и до ожидания завершения дочерней задачи.Therefore, the application can perform additional work after the parent task finishes and before it must wait for the child task to finish.

См. такжеSee also