TaskExtensions.Unwrap Método

Definição

Namespace:

System.Threading.Tasks

Assembly:

System.Runtime.dll

Sobrecargas

Unwrap(Task<Task>)	Cria um proxy Task que representa a operação assíncrona de um Task<Task> (C#) ou Task (Of Task) (Visual Basic).
Unwrap<TResult>(Task<Task<TResult>>)	Cria um proxy Task que representa a operação assíncrona de um Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic).

Unwrap(Task<Task>)

Origem:

TaskExtensions.cs

Cria um proxy Task que representa a operação assíncrona de um Task<Task> (C#) ou Task (Of Task) (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

Parâmetros

task

Task<Task>

O Task<Task> (C#) ou Task (Of Task) (Visual Basic) a ser descompactado.

Retornos

Task

Uma tarefa que representa a operação assíncrona do System.Threading.Tasks.Task(Of Task) fornecido.

Exceções

ArgumentNullException

A exceção lançada se o argumento task for nulo.

Exemplos

O exemplo a seguir mostra como desembrulhar uma tarefa:

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

Comentários

Geralmente, é útil poder retornar uma Tarefa de um Task<TResult>, em que a Tarefa interna representa o trabalho feito como parte do externo Task<TResult>. No entanto, isso resulta em um Task<Task> (C#) ou Task (Of Task) (Visual Basic), que, se não for tratado com cuidado, pode produzir um comportamento inesperado. Desembrulhar resolve esse problema criando uma Tarefa proxy que representa toda a operação assíncrona de tal tarefa.

Confira também

• Biblioteca de tarefas paralelas (TPL)
• Programação assíncrona baseada em tarefas
• Como: Desencapsular uma tarefa aninhada

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

Origem:

TaskExtensions.cs

Cria um proxy Task que representa a operação assíncrona de um Task<Task<T>> (C#) ou Task (Of Task(Of T)) (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)

Parâmetros de tipo

TResult

O tipo de resultado da tarefa.

Parâmetros

task

Task<Task<TResult>>

O Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic) a ser descompactado.

Retornos

Task<TResult>

Um Task que representa a operação assíncrona do Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic) fornecido.

Exceções

ArgumentNullException

A exceção lançada se o argumento task for nulo.

Comentários

Geralmente, é útil poder retornar um Task de um Task, em que a parte interna Task representa o trabalho feito como parte do externo Task. No entanto, isso resulta em um Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic), que, se não for tratado com cuidado, pode produzir um comportamento inesperado. Desembrulhar resolve esse problema criando um proxy Task<TResult> que representa toda a operação assíncrona de um Task<Task<T>> (C#) ou Task (Of Task(Of T)) (Visual Basic).

Confira também

• Biblioteca de tarefas paralelas (TPL)
• Programação assíncrona baseada em tarefas
• Como: Desencapsular uma tarefa aninhada