vb.net - 这是异步工作的好习惯吗？

Question

首先，我在这里搜索并看到了很多类似的问题，但没有一个是我想要的。

我有一个需要一些时间才能返回值的函数为了简化，我们假设它是:

Private Function longProcess() As Boolean
    Threading.Thread.Sleep(10000)
    Return True
End Function

我想运行它并获取它的值，假设单击 Button1

我尝试了以下代码，它运行良好

Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    'some stuff
    Dim output As Boolean = Await Task.Run(Of Boolean)(Function() longProcess())
    'continue another stuff when the longProcess completes
End Sub

这种方式是否足够好？如果没有，可能存在什么问题？

我使用了另一种方法，但由于 Application.DoEvents()

，它使 CPU 使用率更高

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    'some stuff
    Dim awaiter = Task.Run(Of Boolean)(Function() longProcess()).GetAwaiter()
    Do While Not awaiter.IsCompleted
        Application.DoEvents()
    Loop
    Dim output As Boolean = awaiter.GetResult()
    'continue another stuff when the longProcess completes
End Sub

Answer 1

根据评论，您的“长时间运行”函数发送http请求，您应该使用“完全”异步方法，而不需要Task.Run提供额外的线程

Private Async Function SendRequest() As Task(Of Boolean)
    Using (client As New HttpClient())
        client.BaseAddress = new Uri("http://your:api/")

        Dim response As HttpResponseMessage = Await client.GetAsync(pathToResource)

        Return response.IsSuccessStatusCode
    End Using
End Function

然后点击按钮

Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    'some stuff
    Dim output As Boolean = Await SendRequest()
    'continue another stuff when the longProcess completes
End Sub

上面的方法比你使用的Task.Run更好，因为当你从另一个线程发送请求时，该线程什么都不做，只是等待响应。通过使用 HttpClient(或其他一些类)的异步 async-await 方法，整个工作将在一个线程上完成，而不会阻塞应用程序的主 UI 线程。

关于 HttpClient 的注意事项:即使在 Using block 中使用的 HttpClient 示例中，您也应该在应用程序生命周期内仅使用一个实例.

来自微软文档:

HttpClient is intended to be instantiated once and re-used throughout the life of an application. Especially in server applications, creating a new HttpClient instance for every request will exhaust the number of sockets available under heavy loads. This will result in SocketException errors.