VB.NET中Delegate与Await机制及异步重试函数问题咨询

我需要从网络获取URL内容，失败时重试2次，于是编写了接受委托的重试函数，用于在指定次数内重复执行操作直至成功。在调用和实现TryWithRetriesUntilAsync过程中遇到以下疑问：

• 不理解ChatGPT建议添加Return Task.CompletedTask的原因，以及Task.CompletedTask的作用；
• 单行异步Lambda表达式Async Function() result = Await func()的类型为Task(Of Boolean)，而添加Return Task.CompletedTask的多行异步Lambda类型为Task(Of Task)，不清楚类型差异的原因；
• 预期传入Func(Of Task)类型，但实际传入的是Delegate Function类型，对此存在疑惑；
• 多行版异步Lambda能正常运行，但单行版却无法工作，不理解语法差异导致的问题。

相关代码示例 #

基础调用示例 #

Dim jsonstring1 = Await jsonHelper.TryWithRetriesUntilAsync(
    Async Function()
        Await Task.Delay(1000)
        Return "hello world"
    End Function) 

实际使用场景示例 #

Dim jsonstring1 = Await jsonHelper.TryWithRetriesUntilAsync(
    Async Function() 
        Await GetContentFromSomeURL(url)
    End Function) 

重试函数实现 #

Public Shared Async Function TryWithRetriesUntilAsync(action As Func(Of Task), successCondition As Func(Of Boolean), Optional retries As Integer = 3, Optional delayMs As Integer = 2000) As Task
    For attempt As Integer = 1 To retries
        Try
            Await action()
        Catch ex As Exception
            Dim b = 1
            ' 可在此处记录异常
        End Try

        If successCondition() Then
            Exit For
        Else
            Await Task.Delay(delayMs)
        End If
    Next
End Function

Public Shared Async Function TryWithRetriesUntilAsync(func As Func(Of Task(Of String)), Optional retries As Integer = 2, Optional delayMs As Integer = 2000) As Task(Of String)
    Dim result = ""
    Await TryWithRetriesUntilAsync(Async Function() result = Await func(), Function() Not somethingIsWrong(result), retries, delayMs)
    Return result
End Function

ChatGPT建议修改后的代码 #

Await TryWithRetriesUntilAsync(
    Async Function()
        result = Await func()
        Return Task.CompletedTask
    End Function, 
    Function() Not somethingIsWrong(result), retries, delayMs)

类型测试代码 #

Public Shared Async Function TryWithRetriesUntilAsync(func As Func(Of Task(Of String)), Optional retries As Integer = 2, Optional delayMs As Integer = 2000) As Task(Of String)
    Dim result = ""
    Dim hello = Async Function() result = Await func()
    Dim hello1 = Async Function()
                     result = Await func()
                     Return Task.CompletedTask
                 End Function

运行差异示例 #

可正常运行的多行版

Await TryWithRetriesUntilAsync(Async Function()
                                   result = Await func()
                               End Function, Function() Not somethingIsWrong(result), retries, delayMs)

无法工作的单行版

Await TryWithRetriesUntilAsync(Async Function() result = Await func(), Function() Not somethingIsWrong(result), retries, delayMs)

内容的提问来源于stack exchange，提问作者user4951