多线程

Question

我正在开发一个应用程序(在C#中)。它基本上是一个文件上传/下载应用程序(就像filezila一样)。

但它有一个特殊的功能(文件下载)：

我们可以将一个文件分成不同的段(最多100个)。并且可以按不同的周期重复该过程(意味着我们可以将文件分成不同的段，并且可以同时重复该过程不止一次(按周期))。

我在that.In中使用线程的概念，这个应用程序有一些进度条和标签来显示上传/下载状态。

我的问题是：

如果我执行此过程(下载)以获取更多号码，例如:-

100个周期和(周期可以超过100个)

100个细分市场

这意味着我们将一个文件分成100个部分(段)，同样的过程将工作100次(周期)。

意味着100 * 100 =10000个文件将通过相同的进程同时下载。

但我面临的问题是，如果我为这个任务取大数字，那么应该会有更多的线程打开。

如果有100个TCP端口/线程同时运行，则应用程序将挂起。

我尝试了很多方法，但都没有成功yet.Like -

异步委托、ThreadPool等

我在更新进度条和标签时遇到了一个主要问题(因为当前的功能是使用异步委托)。

请给我一些解决这个问题的方法。

Answer 1

由于所有这些线程都希望将数据传递给UI线程以显示进度，因此UI线程正在成为应用程序的瓶颈。

您可以添加一个计时器，该计时器会不时地使UI线程检查作业的进度。

这样，UI线程不是由大量的线程驱动的，而是由时间驱动的。

如果您需要更多详细信息，请发布一些代码。

Answer 2

你好，Erno，我正在发送一些代码，以便更好地理解：

这是下载函数：

Public Sub FileDownload()

    txtBytesToDownload.Text = totalBytesToDownload.ToString("N", nfi)  'set textbox with total file size

    del = New MyDelegate(AddressOf DownloadDataInRange)

    callback = New AsyncCallback(AddressOf CalcCallback)


    TotalBytesToDownloadForEachCycle = totalBytesToDownload
    downloadedBytes = 0
    dlStopWatch = Stopwatch.StartNew()

    Dim flag As Integer = 0

    Dim segment As Integer = nuSegment.Value          'total segments
    Dim cyl = cycleNumericUpDown.Value                'total cycles

    'ServicePointManager.DefaultConnectionLimit = segment

    If UtilityFunctions.CheckRangeSupported(dlUrlHttpTextBox.Text) Then

        Dim segmentSize As Integer = 0
        segmentSize = TotalBytesToDownloadForEachCycle / segment

        ' For cy As Integer = 0 To (cyl - 1)

        For ctr As Integer = 0 To (segment - 1)        'loop for total Segments

            GC.Collect()
            flag += 1

            Dim fileValues As New FileValues()

            If ctr = 0 Then
                fileValues.StartPoint = 0               'starting point of each segment (in bytes)
            Else
                fileValues.StartPoint = segmentSize * ctr + 1
            End If

            fileValues.EndPoint = fileValues.StartPoint + segmentSize   'end point of each segment (in bytes)

            If (ctr = (segment - 1)) Then
                fileValues.EndPoint += TotalBytesToDownloadForEachCycle Mod segment
            End If

            fileValues.URL = dlUrlHttpTextBox.Text                         'downloading file url
            Dim str As String = ctr.ToString() + "_" + flag.ToString()

            ' del.BeginInvoke(fileValues, callback, Nothing)


            newThread = New System.Threading.Thread(AddressOf DownloadBytes)      'Thread starts here
            newThread.Priority = ThreadPriority.Highest
            newThread.IsBackground = True
            newThread.Start(fileValues)

            'ThreadPool.QueueUserWorkItem(AddressOf DownloadBytes, fileValues)

            fileValues = Nothing

        Next

        ' ProgressBarTotal.Value += 1

        ' Next

    Else
        Dim fileValues As New FileValues()
        fileValues.StartPoint = 0
        fileValues.EndPoint = TotalBytesToDownloadForEachCycle
        fileValues.URL = dlUrlHttpTextBox.Text
        Dim newThread As New System.Threading.Thread(AddressOf DownloadBytes)
        newThread.Name = "Thread1"
        newThread.Start(fileValues)
        'ThreadPool.QueueUserWorkItem(AddressOf DownloadBytes, fileValues)
        fileValues = Nothing

    End If

    Console.WriteLine("Http Downloload End")
    Debug.Print("thread List 1 count =" + _threadsList1.Count.ToString() + ", thread list 2 count =" + _threadsList2.Count.ToString() + ", thread list 3 count =" + _threadsList3.Count.ToString())

    'MessageBox.Show("finished - flag=" + flag.ToString())

    'After all Cycles Complete 
    'startButton.Enabled = True
    'abortButton.Enabled = False
    'skipButton.Enabled = False
    'DataGridViewDLOrPing.Enabled = True
    'DataGridViewUL.Enabled = True

    'protocolComboBox.Enabled = True
    'modelComboBox.Enabled = True
    'testTypeComboBox.Enabled = True
    'measurementComboBox.Enabled = True
    'cycleNumericUpDown.Enabled = True
    'DelayNumericUpDown.Enabled = True
    'InputBoxPrivilege()

End Sub

这是Thread将调用以读取字节的函数：

Public Sub DownloadBytes(ByVal p_fileValues As FileValues)

    Dim httpWebRequest As HttpWebRequest
    Dim httpWebResponse As HttpWebResponse
    Dim responseStream As Stream

    Dim threadName = threadID

    Try
        Console.WriteLine("Start " + Thread.CurrentThread.Name)
        httpWebRequest = DirectCast(WebRequest.Create(p_fileValues.URL), HttpWebRequest)
        'httpWebRequest.ProtocolVersion = HttpVersion.Version11
        httpWebRequest.KeepAlive = False
        httpWebRequest.AddRange(p_fileValues.StartPoint, p_fileValues.EndPoint)
        httpWebRequest.Credentials = CredentialCache.DefaultCredentials
        httpWebRequest.Proxy = WebRequest.DefaultWebProxy
        httpWebResponse = CType(httpWebRequest.GetResponse(), HttpWebResponse)
        responseStream = httpWebResponse.GetResponseStream()

        Dim bytesSize As Integer = 0
        ' A buffer for storing and writing the data retrieved from the server
        Dim downBuffer As Byte() = New Byte(2047) {}
        Dim bytesAlreadyDownloaded As Int64 = p_fileValues.StartPoint

        ' Loop through the buffer until the buffer is empty
        While (True)

            'end while loop if the Abort button is clicked
            If (isActionAborted = True) Then
                Exit While
            End If

            'currentCycle is > total Cycles ,then end while
            If (currentCycleDownload > cycleNumericUpDown.Value) Then
                Exit While
            End If

            bytesSize = responseStream.Read(downBuffer, 0, downBuffer.Length)

            bytesAlreadyDownloaded += bytesSize

            'speedtimer.Start()

            If (bytesSize <= 0) Then
                If (downloadedBytes < totalBytesToDownload) Then
                    Me.Invoke(New UploadProgressCallback(AddressOf Me.UpdateDownloadProgress), New Object() {(totalBytesToDownload - downloadedBytes), totalBytesToDownload})
                End If

                Exit While
            End If

            ' Invoke the method that updates the form's label and progress bar
            Me.Invoke(New DownloadProgressCallback(AddressOf Me.UpdateDownloadProgress), New Object() {bytesSize, TotalBytesToDownloadForEachCycle})

            If (bytesAlreadyDownloaded > p_fileValues.EndPoint) Then
                'Console.WriteLine("Downloading part files Exit " + p_fileValues.StartPoint.ToString() + "," + p_fileValues.EndPoint.ToString())
                Exit While
            End If

        End While

        responseStream.Flush()
        responseStream.Close()
        httpWebResponse.Close()
        responseStream.Dispose()
        responseStream = Nothing
        httpWebResponse = Nothing
        Console.WriteLine("End " + Thread.CurrentThread.Name)

        'ProgressDownload.Value = Convert.ToInt32((downloadedBytes * 100) / totalBytesToDownload)
        ' downloadedBytesTextBox.Text = downloadedBytes.ToString("N", nfi)

    Catch ex As Exception

        Console.WriteLine("Error " + Thread.CurrentThread.Name)
        Console.WriteLine(ex)

    Finally
        Console.WriteLine("Finally " + Thread.CurrentThread.Name)

        GC.Collect()

        ' GC.WaitForPendingFinalizers()
        'newThread.Abort()


        'Try
        'Thread.CurrentThread.Abort()

        'Catch ex1 As Exception

        'End Try
    End Try

    'Return 1

End Sub

此函数将更新表单上的进度条和其他标签：

Private Sub UpdateDownloadProgress(ByVal BytesRead As Int64, ByVal TotalBytes As Int64)
    If Not swDL Is Nothing AndAlso swDL.IsRunning Then
        swDL.Stop()
        If swDL.ElapsedMilliseconds > 0 Then
            resultGrid.Rows.Item(HandoverGridCounter - 1).Cells(4).Value &= "DL: " & swDL.ElapsedMilliseconds & " ms"
        End If
        swDL = Nothing
    End If


    If (dlCurrentspeed > 0) Then
        'txtCurrentSpeedDL.Text = Math.Round((dlCurrentspeed / 1024), 0) & " KB/s"
    End If


    downloadedBytes += BytesRead
    If downloadedBytes >= totalBytesToDownload Then
        downloadedBytes = totalBytesToDownload
    End If

    ProgressDownload.Value = Convert.ToInt32((downloadedBytes * 100) / TotalBytes)
    downloadedBytesTextBox.Text = downloadedBytes.ToString("N", nfi)  ' & " bytes"

    If totalBytesToDownload = 0 Then
        totalBytesToDownload = TotalBytes
        txtBytesToDownload.Text = totalBytesToDownload.ToString("N", nfi)
    End If

    If downloadedBytes >= totalBytesToDownload Then
        dlCurrentspeed = 0
        dlStopWatch.Stop()

        testEndTickDownload = My.Computer.Clock.TickCount
        testDeltaDownload = (testEndTickDownload - testStartTickDownload) / 1000
        If DLtimedOut = True Then
            DownloadCompleted(TestStatus.Cancelled.ToString(), "")
        Else
            DownloadCompleted(TestStatus.Completed.ToString(), "")
        End If
        If currentCycleDownload <= cycleNumericUpDown.Value Then
            If protocolComboBox.Text = "HTTP" Then
                StartHttpDownload()
            Else
                StartFtpDownload()
            End If
        End If
    End If
End Sub

Answer 3

要从工作线程(无论是显式创建的、排队到线程池的工作项还是来自异步应用编程接口的回调)异步更新UI，请使用Control.BeginInvoke。

这不会在等待UI线程处理操作时阻塞辅助线程。

但请记住，UI线程不能假定异步操作完成的特定顺序(以特定顺序启动的两个对等的下载不太可能按该顺序完成:太多的外部因素会影响下载速度)。

最后，大多数BeginABC方法都需要调用相应的EndABC，但(有帮助的) Control.BeginInvoke不需要。