TaskExtensions.Unwrap Méthode

Définition

Espace de noms:

System.Threading.Tasks

Assembly:

System.Runtime.dll

Surcharges

Unwrap(Task<Task>)	Crée un proxy Task qui représente l'opération asynchrone d'un Task<Task> (en C#) ou Task (Of Task) (en Visual Basic).
Unwrap<TResult>(Task<Task<TResult>>)	Crée un proxy Task qui représente l'opération asynchrone d'un Task<Task<T>> (en C#) ou Task (Of Task(Of T)) (en Visual Basic).

Unwrap(Task<Task>)

Source:

TaskExtensions.cs

Crée un proxy Task qui représente l'opération asynchrone d'un Task<Task> (en C#) ou Task (Of Task) (en Visual Basic).

public:
[System::Runtime::CompilerServices::Extension]
 static System::Threading::Tasks::Task ^ Unwrap(System::Threading::Tasks::Task<System::Threading::Tasks::Task ^> ^ task);

public static System.Threading.Tasks.Task Unwrap (this System.Threading.Tasks.Task<System.Threading.Tasks.Task> task);

static member Unwrap : System.Threading.Tasks.Task<System.Threading.Tasks.Task> -> System.Threading.Tasks.Task

<Extension()>
Public Function Unwrap (task As Task(Of Task)) As Task

Paramètres

task

Task<Task>

Le Task<Task> (C#) ou Task (Of Task) (Visual Basic) à défaire.

Retours

Task

Tâche qui représente l'opération asynchrone de la System.Threading.Tasks.Task(Of Task) fournie.

Exceptions

ArgumentNullException

L'exception levée si l'argument task est null.

Exemples

L’exemple suivant montre comment désencapsuler une tâche :

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

class UnWrapDemo
{
     // Demonstrated features:
        //		Task.Unwrap()
        // 		Task.Factory.StartNew()
        //		Task.ContinueWith()
        // Expected results:
        // 		Indicates that continuation chains can be set up virtually instantaneously using Unwrap(), and then left to run on their own.
        //      The results of the RemoteIncrement(0) chain and the RemoteIncrement(4) chain may be intermixed with each other.
        //		The results of the sequence that starts with RemoteIncrement(4) are in strict order.
        // Documentation:
        //		http://msdn.microsoft.com/library/dd781129(VS.100).aspx
        // More information:
        //		http://blogs.msdn.com/pfxteam/archive/2009/11/04/9917581.aspx
        // Other notes:
        //		The combination of Task<T>, ContinueWith() and Unwrap() can be particularly useful for setting up a chain of long-running
        //      tasks where each task uses the results of its predecessor.
        static void Main()
        {
            // Invoking individual tasks is straightforward
            Task<int> t1 = RemoteIncrement(0);
            Console.WriteLine("Started RemoteIncrement(0)");

            // Chain together the results of (simulated) remote operations.
            // The use of Unwrap() instead of .Result below prevents this thread from blocking while setting up this continuation chain.
            Task<int> t2 = RemoteIncrement(4)
                .ContinueWith(t => RemoteIncrement(t.Result))			// RemoteIncrement() returns Task<int> so no unwrapping is needed for the first continuation.
                .Unwrap().ContinueWith(t => RemoteIncrement(t.Result))	// ContinueWith() returns Task<Task<int>>. Therefore unwrapping is needed.
                .Unwrap().ContinueWith(t => RemoteIncrement(t.Result))	// and on it goes...
                .Unwrap();
            Console.WriteLine("Started RemoteIncrement(...(RemoteIncrement(RemoteIncrement(4))...)");

            try
            {
                t1.Wait();
                Console.WriteLine("Finished RemoteIncrement(0)\n");

                t2.Wait();
                Console.WriteLine("Finished RemoteIncrement(...(RemoteIncrement(RemoteIncrement(4))...)");
            }
            catch (AggregateException e)
            {
                Console.WriteLine("A task has thrown the following (unexpected) exception:\n{0}", e);
            }
        }
        // This method represents a remote API.
        static Task<int> RemoteIncrement(int n)
        {
            return Task<int>.Factory.StartNew(
                (obj) =>
                {
                    // Simulate a slow operation
                    Thread.Sleep(1 * 1000);

                    int x = (int)obj;
                    Console.WriteLine("Thread={0}, Next={1}", Thread.CurrentThread.ManagedThreadId, ++x);
                    return x;
                },
                n);
        }
}

Imports System.Threading
Imports System.Threading.Tasks

Module UnwrapDemo
    ' Demonstrated features:
    '   Task.Unwrap()
    '    Task.Factory.StartNew()
    '   Task.ContinueWith()
    ' Expected results:
    ' 	Indicates that continuation chains can be set up virtually instantaneously using Unwrap(), and then left to run on their own.
    '   The results of the RemoteIncrement(0) chain and the RemoteIncrement(4) chain may be intermixed with each other.
    '   The results of the sequence that starts with RemoteIncrement(4) are in strict order.
    ' Documentation:
    '   http://msdn.microsoft.com/library/dd781129(VS.100).aspx
    ' More information:
    '   http://blogs.msdn.com/pfxteam/archive/2009/11/04/9917581.aspx
    ' Other notes:
    '   The combination of Task<T>, ContinueWith() and Unwrap() can be particularly useful for setting up a chain of long-running
    '   tasks where each task uses the results of its predecessor.

    Sub Main()
        ' Invoking individual tasks is straightforward
        Dim t1 As Task(Of Integer) = RemoteIncrement(0)
        Console.WriteLine("Started RemoteIncrement(0)")

        ' Chain together the results of (simulated) remote operations.
        ' The use of Unwrap() instead of .Result below prevents this thread from blocking while setting up this continuation chain.
        ' RemoteIncrement() returns Task<int> so no unwrapping is needed for the first continuation.
        ' ContinueWith() here returns Task<Task<int>>. Therefore unwrapping is needed.
        ' and on it goes...
        Dim t2 As Task(Of Integer) = RemoteIncrement(4).ContinueWith(Function(t) RemoteIncrement(t.Result)).Unwrap().ContinueWith(Function(t) RemoteIncrement(t.Result)).Unwrap().ContinueWith(Function(t) RemoteIncrement(t.Result)).Unwrap()
        Console.WriteLine("Started RemoteIncrement(...(RemoteIncrement(RemoteIncrement(4))...)")

        Try
            t1.Wait()
            Console.WriteLine("Finished RemoteIncrement(0)" & vbLf)

            t2.Wait()
            Console.WriteLine("Finished RemoteIncrement(...(RemoteIncrement(RemoteIncrement(4))...)")
        Catch e As AggregateException
            Console.WriteLine("A task has thrown the following (unexpected) exception:" & vbLf & "{0}", e)

        End Try
    End Sub

    ' This method represents a remote API.
    Function RemoteIncrement(ByVal n As Integer) As Task(Of Integer)
        Return Task(Of Integer).Factory.StartNew(Function(obj)
                                                     ' Simulate a slow operation
                                                     Thread.Sleep(1 * 1000)

                                                     Dim x As Integer = CInt(obj)
                                                     Console.WriteLine("Thread={0}, Next={1}", Thread.CurrentThread.ManagedThreadId, System.Threading.Interlocked.Increment(x))
                                                     Return x
                                                 End Function, n)
    End Function


End Module

Remarques

Il est souvent utile de pouvoir retourner une tâche à partir d’un Task<TResult>, où la tâche interne représente le travail effectué dans le cadre du .Task<TResult> Toutefois, cela entraîne un Task<Task> (C#) ou Task (Of Task) (Visual Basic), qui, s’il n’est pas traité avec soin, peut produire un comportement inattendu. Unwrap résout ce problème en créant une tâche proxy qui représente l’ensemble de l’opération asynchrone d’une telle tâche.

Voir aussi

• Bibliothèque parallèle de tâches
• Programmation asynchrone basée sur les tâches
• Procédure : désencapsuler une tâche imbriquée

Unwrap<TResult>(Task<Task<TResult>>)

Source:

TaskExtensions.cs

Crée un proxy Task qui représente l'opération asynchrone d'un Task<Task<T>> (en C#) ou Task (Of Task(Of T)) (en Visual Basic).

public:
generic <typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Threading::Tasks::Task<TResult> ^ Unwrap(System::Threading::Tasks::Task<System::Threading::Tasks::Task<TResult> ^> ^ task);

public static System.Threading.Tasks.Task<TResult> Unwrap<TResult> (this System.Threading.Tasks.Task<System.Threading.Tasks.Task<TResult>> task);

static member Unwrap : System.Threading.Tasks.Task<System.Threading.Tasks.Task<'Result>> -> System.Threading.Tasks.Task<'Result>

<Extension()>
Public Function Unwrap(Of TResult) (task As Task(Of Task(Of TResult))) As Task(Of TResult)

Paramètres de type

TResult

Type du résultat de la tâche.

Paramètres

task

Task<Task<TResult>>

Le Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic) à défaire.

Retours

Task<TResult>

Un Task qui représente l'opération asynchrone du Task<Task<T>> fourni (C#) ou Task (Of Task(Of T)) (Visual Basic).

Exceptions

ArgumentNullException

L'exception levée si l'argument task est null.

Remarques

Il est souvent utile de pouvoir retourner un Task à partir d’un Task, où l’interne Task représente le travail effectué dans le cadre du .Task Toutefois, cela entraîne un Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic), qui, s’il n’est pas traité avec soin, peut produire un comportement inattendu. Unwrap résout ce problème en créant un proxy Task<TResult> qui représente l’ensemble de l’opération asynchrone d’un Task<Task<T>> tel (C#) ou Task (Of Task(Of T)) (Visual Basic).

Voir aussi

• Bibliothèque parallèle de tâches
• Programmation asynchrone basée sur les tâches
• Procédure : désencapsuler une tâche imbriquée