非阻塞 webrequests vb.net [英] non blocking webrequests vb.net

问题描述

我正在制作一个必须尽快处理大约 5000 个字符串的程序.其中大约 2000 个字符串必须通过网络请求翻译到 mymemory.translated.net.(见下面的代码，这里不需要 JSON 部分)

I am making a program that must process about 5000 strings as quickly as possible. about 2000 of these strings must be translated via a webrequest to mymemory.translated.net. (see code below, JSON part removed since not needed here)

Try

          url = "http://api.mymemory.translated.net/get?q=" & Firstpart & "!&langpair=de|it&de=[e-mail]"

          request = DirectCast(WebRequest.Create(url), HttpWebRequest)
          response = DirectCast(request.GetResponse(), HttpWebResponse)
          myreader = New StreamReader(response.GetResponseStream())

          Dim rawresp As String
          rawresp = myreader.ReadToEnd()
          Debug.WriteLine("Raw:" & rawresp)


          Catch ex As Exception
              MessageBox.Show(ex.ToString)

          End Try

代码本身工作正常，问题是它是一个阻塞代码，每个字符串需要大约 1 秒.对于我的所有琴弦，这多于半小时.我需要将此代码转换为非阻塞代码并同时进行多个调用.有人可以告诉我我该怎么做吗?我正在考虑使用后台工作者，但这不会加快速度......它只会在不同的线程上执行代码......

the code itself is working fine, problem is it is a blocking code and needs about 1 second per string. Thats more then half an hour for all my strings. i would need to convert this code to a non blocking one and make multiple calls on the same time. Could somebody please tell me how i could do that? I was thinking of a background worker but that wouldnt speed things up.. it would just execute the code on a different thread...

谢谢！

推荐答案

问题在于，您不仅仅被并发操作的最大数量所阻碍.HttpWebRequests 受到自然限制(我相信默认策略在任何给定时间只允许 2 个)，因此您也必须覆盖该行为.请参考下面的代码.

The problem is you aren't just being held back by the maximum number of concurrent operations. HttpWebRequests are throttled by nature (I believe the default policy allows only 2 at any given time), so you have to override that behaviour too. Please refer to the code below.

Imports System.Diagnostics
Imports System.IO
Imports System.Net
Imports System.Threading
Imports System.Threading.Tasks

Public Class Form1

  ''' <summary>
  ''' Test entry point.
  ''' </summary>
  Private Sub Form1_Load() Handles MyBase.Load
    ' Generate enough words for us to test thoroughput.
    Dim words = Enumerable.Range(1, 100) _
      .Select(Function(i) "Word" + i.ToString()) _
      .ToArray()

    ' Maximum theoretical number of concurrent requests.
    Dim maxDegreeOfParallelism = 24
    Dim sw = Stopwatch.StartNew()

    ' Capture information regarding current SynchronizationContext
    ' so that we can perform thread marshalling later on.
    Dim uiScheduler = TaskScheduler.FromCurrentSynchronizationContext()
    Dim uiFactory = New TaskFactory(uiScheduler)

    Dim transformTask = Task.Factory.StartNew(
      Sub()
        ' Apply the transformation in parallel.
        ' Parallel.ForEach implements clever load
        ' balancing, so, since each request won't
        ' be doing much CPU work, it will spawn
        ' many parallel streams - likely more than
        ' the number of CPUs available.
        Parallel.ForEach(words, New ParallelOptions With {.MaxDegreeOfParallelism = maxDegreeOfParallelism},
          Sub(word)
            ' We are running on a thread pool thread now.
            ' Be careful not to access any UI until we hit
            ' uiFactory.StartNew(...)

            ' Perform transformation.
            Dim url = "http://api.mymemory.translated.net/get?q=" & word & "!&langpair=de|it&de=[e-mail]"
            Dim request = DirectCast(WebRequest.Create(url), HttpWebRequest)

            ' Note that unless you specify this explicitly,
            ' the framework will use the default and you
            ' will be limited to 2 parallel requests
            ' regardless of how many threads you spawn.
            request.ServicePoint.ConnectionLimit = maxDegreeOfParallelism

            Using response = DirectCast(request.GetResponse(), HttpWebResponse)
              Using myreader As New StreamReader(response.GetResponseStream())
                Dim rawresp = myreader.ReadToEnd()

                Debug.WriteLine("Raw:" & rawresp)

                ' Transform the raw response here.
                Dim processed = rawresp

                uiFactory.StartNew(
                  Sub()
                    ' This is running on the UI thread,
                    ' so we can access the controls,
                    ' i.e. add the processed result
                    ' to the data grid.
                    Me.Text = processed
                  End Sub, TaskCreationOptions.PreferFairness)
              End Using
            End Using
          End Sub)
      End Sub)

    transformTask.ContinueWith(
      Sub(t As Task)
        ' Always stop the stopwatch.
        sw.Stop()

        ' Again, we are back on the UI thread, so we
        ' could access UI controls if we needed to.
        If t.Status = TaskStatus.Faulted Then
          Debug.Print("The transformation errored: {0}", t.Exception)
        Else
          Debug.Print("Operation completed in {0} s.", sw.ElapsedMilliseconds / 1000)
        End If
      End Sub,
      uiScheduler)
  End Sub

End Class

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