问题是您不仅受到最大并发操作数的阻碍。HttpWebRequests本质上会受到限制（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。
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=somemail@christmas.com"
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