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在TPL中快速抛出未处理的异常

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我的问题：我想在.NET 4和_644366下的WinForms应用程序中使用TPL吗？有可能吗？

在支持 async/await 支持的.NET 4.5中，可以编写：

Public Class AwaitForm
    Inherits Form

    Private Async Sub Execute()
        Dim uiScheduler = TaskScheduler.FromCurrentSynchronizationContext()

        Try
            Await Me.LongWork().
                ContinueWith(Sub(t) Me.LongWorkCompleted(), uiScheduler)

        Catch ex As Exception
            ' yay, possible to handle here
            ' eg. MsgBox(ex.Message)
            Throw
        End Try
    End Sub

    Private Async Function LongWork() As Task
        Await Task.Delay(1000)
    End Function

    Private Sub LongWorkCompleted()
        Throw New Exception("Ups")
    End Sub

End Class

如果未在 Excecute 方法中处理，则会立即抛出continuation中的异常 .

如何在没有 async/await 支持的情况下在.NET 4中实现相同的行为？

.net vb.net asynchronous task-parallel-library

2 回答

  • 1

    首先，您应该知道可以使用async-await与.Net 4.0一起使用Microsoft.Bcl.Async

    但是没有它，你可以使用 ContinueWith 为任务添加一个延续，并让它只在 TaskContinuationOptions.OnlyOnFaulted 出现异常时运行

    Me.LongWork().ContinueWith(Sub(task) MsgBox(task.Exception.Message), CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted)
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  • 1

    1）可以使用 Microsoft.Bcl.Async 作为i3arnon建议 .

    2）或者，如果您不想引用额外的库，我已经提出了基于 async/await 的解决方案 . 背后的魔力是令人讨厌的，但它已经得到了 .

    Imports System.Reflection
Imports System.Runtime.CompilerServices
Imports System.Threading


Public Module TaskExtensions

    ''' <summary>Throws the exception on the current SynchronizationContext or ThreadPool if there is none.</summary>
    ''' <param name="task">Task whose faulted continuation should throw exception.</param>
    <Extension()>
    Public Sub ThrowOnFaulted(task As Task)
        Dim context = SynchronizationContext.Current
        ThrowOnFaulted(task, context)
    End Sub


    ''' <summary>Throws the exception on the ThreadPool in given context.</summary>
    ''' <param name="task">Task whose faulted continuation should throw exception.</param>
    ''' <param name="targetContext">The target context on which to propagate the exception. Null to use the ThreadPool.</param>
    <Extension()>
    Public Sub ThrowOnFaulted(task As Task, targetContext As SynchronizationContext)
        task.ContinueWith(Sub(t) ThrowOnFaultedCore(t, targetContext), TaskContinuationOptions.OnlyOnFaulted)
    End Sub


    ''' <remarks>Taken from System.RunTime.CompilerServices.AsyncServices.</remarks>
    Private Sub ThrowOnFaultedCore(task As Task, targetContext As SynchronizationContext)
        Dim exception = task.Exception

        If targetContext IsNot Nothing Then
            Try
                targetContext.Post(Sub(state) Throw DirectCast(state, Exception), exception)
                Return
            Catch ex As Exception
                exception = New AggregateException({exception, ex})
            End Try
        End If

        ThreadPool.QueueUserWorkItem(Sub(state) Throw DirectCast(state, Exception), exception)
    End Sub

End Module

    它符合要求 - 抛出异常"fast"并且可以处理 . 异常是 Post 编辑到目标 SynchronizationContext ，因此远离快速和同步的TPL 's exception trapping mechanism. It'，但至少它比等待任务处理更好 .

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