TaskExtensions.Unwrap 方法

定义

重载

Unwrap(Task<Task>)

创建一个表示 Task 的异步操作的代理 TryExecuteTaskInline(Task, Boolean)Creates a proxy Task that represents the asynchronous operation of a TryExecuteTaskInline(Task, Boolean).

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

创建一个表示 Task 的异步操作的代理 Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic)。Creates a proxy Task that represents the asynchronous operation of a Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic).

Unwrap(Task<Task>)

创建一个表示 Task 的异步操作的代理 TryExecuteTaskInline(Task, Boolean)Creates a proxy Task that represents the asynchronous operation of a TryExecuteTaskInline(Task, Boolean).

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

参数

task
Task<Task>

要解包的 Task<Task> (C#) 或者 Task (Of Task) (Visual Basic)。The Task<Task> (C#) or Task (Of Task) (Visual Basic) to unwrap.

返回

Task

表示所提供的 System.Threading.Tasks.Task(Of Task) 的异步操作的 Task。A Task that represents the asynchronous operation of the provided System.Threading.Tasks.Task(Of Task).

例外

task 参数为 null 时引发的异常。The exception that is thrown if the task argument is null.

示例

下面的示例演示如何解包任务:The following example shows how to unwrap a task:

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

注解

如果能够从中返回任务,则这通常很有用 Task<TResult> ,其中内部任务表示作为外部工作完成的工作 Task<TResult>It is often useful to be able to return a Task from a Task<TResult>, where the inner Task represents work done as part of the outer Task<TResult>. 不过,这样做 Task<Task> 会导致(c #)或 Task (Of Task) (Visual Basic),如果不仔细处理此操作,可能会产生意外行为。However, doing so results in a Task<Task> (C#) or Task (Of Task) (Visual Basic), which, if not dealt with carefully, could produce unexpected behavior. 解包通过创建代表此类任务的整个异步操作的代理任务来解决此问题。Unwrap solves this problem by creating a proxy Task that represents the entire asynchronous operation of such a task.

另请参阅

适用于

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

创建一个表示 Task 的异步操作的代理 Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic)。Creates a proxy Task that represents the asynchronous operation of a Task<Task<T>> (C#) or 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)

类型参数

TResult

任务结果的类型。The type of the task's result.

参数

task
Task<Task<TResult>>

要解包的 Task<Task<T>> (C#) 或者 Task (Of Task(Of T)) (Visual Basic)。The Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic) to unwrap.

返回

Task<TResult>

一个 Task 它表示所提供的 Task<Task<T>> (C#) 或 Task (Of Task(Of T)) (Visual Basic) 的异步运算。A Task that represents the asynchronous operation of the provided Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic).

例外

task 参数为 null 时引发的异常。The exception that is thrown if the task argument is null.

注解

通常 Task ,能够从返回 Task ,其中内部 Task 表示作为外部工作完成的工作 TaskIt is often useful to be able to return a Task from a Task, where the inner Task represents work done as part of the outer Task. 不过,这样做 Task<Task<T>> 会导致(c #)或 Task (Of Task(Of T)) (Visual Basic),如果不仔细处理此操作,可能会产生意外行为。However, doing so results in a Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic), which, if not dealt with carefully, could produce unexpected behavior. 解包通过创建 Task<TResult> 表示此类 Task<Task<T>> (c #)或(Visual Basic)的整个异步操作的代理来解决此问题 Task (Of Task(Of T))Unwrap solves this problem by creating a proxy Task<TResult> that represents the entire asynchronous operation of such a Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic).

另请参阅

适用于