Question

我有这个奇怪的问题。我需要从后台工作程序中调用一个进程

Private Shared _process As Process
Private Shared _StartInfo As ProcessStartInfo
Private WithEvents _bwConvertMedia As New BackgroundWorker

以下是DoWorkAsync中的工作

Private Async Sub _bwConvertMedia_DoWorkAsync(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles _bwConvertMedia.DoWork
  For AI = 1 To 100
    _StartInfo = New ProcessStartInfo(".\mycmd.exe", "-1")
    _StartInfo.RedirectStandardOutput = True
    _StartInfo.UseShellExecute = False
    _StartInfo.CreateNoWindow = True
    _StartInfo.RedirectStandardError = True

    _process = New Process() With {.EnableRaisingEvents = True, .StartInfo = _StartInfo}
    AddHandler _process.OutputDataReceived, AddressOf OutputHandler
    AddHandler _process.ErrorDataReceived, AddressOf ErrorHandler
    AddHandler _process.Exited, AddressOf Exited
    Try
      aSuccess = Await AwaitProcess()
    Catch ex As Exception
    End Try
    _bwConvertMedia.ReportProgress(ai)
  Next

在这里

Private Shared Async Function AwaitProcess() As Task(Of Integer)
  _tcs = New TaskCompletionSource(Of Integer)
  _status.Converting = True
  _Error.Clear()
  _process.Start()
  _process.BeginErrorReadLine()
  _process.BeginOutputReadLine()    
  Return Await _tcs.Task
End Function

问题是，当执行Await _tcs.Task时，会执行_bwConvertMedia RunWorkerCompleted过程，所以当我调用_bwConvertMedia.ReportProgress（ai）时

我收到工人已经完成的错误。

为什么？你能救我吗？

会发生什么

DoWork - 迭代1
在等待过程1
RunWorkerComplete
DoWork迭代2-100

正确的行为是后台工作程序调用该过程100次，然后它完成执行并调用RunWorkerCompleted

Answer 1

我对之前链接的代码进行了一些修改，这里是使用Task.Factory的顺序非阻塞Async / Await过程和非阻塞并行过程的两个示例。

由于我无法测试您的程序，因此我只使用了Tracert.exe 模拟stdout结果以更新用户界面。

为了使正在运行的任务/线程与UI同步，我在第一种情况下使用了进程的.SynchronizingObject，在第二种情况下使用了TaskScheduler方法TaskScheduler.FromCurrentSynchronizationContext()。

Tracert.exe的输出传递给两个TextBox。在并行示例中，我在Tasks之间插入了1秒的延迟，以查看两个TextBox如何更新。

Async / Await示例可以修改为以不同方式工作，因为您无需等待任务完成以启动另一个任务。

使用ProcessStartInfo和Process将List(Of ProcessStartInfo)和List(Of Process)个对象添加到池。

这两个例子都使用了这些。定义正确的范围。

Public psInfoPool As List(Of ProcessStartInfo)
Public ProcessPool As List(Of Process)

顺序异步/等待

委托与SynchronizingObject.BeginInvoke if一起使用 InvokeRequired = true

Public Delegate Sub UpdUI(_object As TextBox, _value As String)

Public Sub UpdateUIDelegate(control As TextBox, _input As String)
    control.AppendText(_input)
End Sub

    Dim NumberOfProcesses As Integer
    For x = 0 To 1
        Dim OutCtl As TextBox = If(x = 0, Me.TextBox1, Me.TextBox2)
        Dim _result As Integer = Await Task.Run(Async Function() As Task(Of Integer)
                                     Return Await Test_SequentialAsync("192.168.1.1", OutCtl)
                                 End Function)
        NumberOfProcesses += _result
    Next

MediaToConvert参数将是文件的名称根据需要调整示例时进行转换。 OutCtl 参数只是用于输出的TextBox

Public Async Function Test_SequentialAsync(ByVal MediaToConvert As String, OutCtl As TextBox) As Task(Of Integer)
    Dim _CurrentProcessInfo As Integer
    Dim _CurrentProcess As Integer

    Dim ExitCode As Integer = Await Task.Run(Function() As Integer

        Dim _processexitcode As Integer

        psInfoPool.Add(New ProcessStartInfo)
        _CurrentProcessInfo = psInfoPool.Count - 1
        psInfoPool(_CurrentProcessInfo).RedirectStandardOutput = True
        psInfoPool(_CurrentProcessInfo).CreateNoWindow = True
        psInfoPool(_CurrentProcessInfo).UseShellExecute = False
        'Name of the executable to start
        psInfoPool(_CurrentProcessInfo).FileName = "Tracert"    'psInfo.FileName = ".\mycmd.exe"""
        'Parameter(s) to pass to the executable
        psInfoPool(_CurrentProcessInfo).Arguments = MediaToConvert
        psInfoPool(_CurrentProcessInfo).WindowStyle = ProcessWindowStyle.Hidden

        ProcessPool.Add(New Process)
        _CurrentProcess = ProcessPool.Count - 1

        ProcessPool(_CurrentProcess) = New Process() With {.StartInfo = psInfoPool(_CurrentProcessInfo),
                                                           .EnableRaisingEvents = True,
                                                           .SynchronizingObject = Me}

        ProcessPool(_CurrentProcess).Start()
        ProcessPool(_CurrentProcess).BeginOutputReadLine()
        AddHandler ProcessPool(_CurrentProcess).OutputDataReceived,
            Sub(sender As Object, e As DataReceivedEventArgs)
                    If e.Data IsNot Nothing Then
                        If ProcessPool(_CurrentProcess).SynchronizingObject.InvokeRequired Then
                            ProcessPool(_CurrentProcess).SynchronizingObject.BeginInvoke(
                                                         New UpdUI(AddressOf UpdateUIDelegate),
                                                         New Object() {OutCtl,
                                                         e.Data + Environment.NewLine})
                        Else
                            OutCtl.AppendText(e.Data + Environment.NewLine)
                        End If
                    End If
            End Sub

        'Add an event handler for the Exited event
        AddHandler ProcessPool(_CurrentProcess).Exited,
                Sub(source As Object, ev As EventArgs)
                    _processexitcode = ProcessPool(_CurrentProcess).ExitCode
                    Console.WriteLine("The process has exited. Code: {0}  Time: {1}",
                    _processexitcode,
                    ProcessPool(_CurrentProcess).ExitTime)
                End Sub

        ProcessPool(_CurrentProcess).WaitForExit()
        ProcessPool(_CurrentProcess).Close()
        Return _processexitcode
    End Function)

    Return If(ExitCode = 0, 1, 0)

End Function

使用Task.Fatory的并行进程

定义计划程序并将其与当前上下文相关联

Public _Scheduler As TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext()

要使用Await Task.Delay(1000)，您必须使用Async方法，但是它只是用于测试输出，不需要它。

For x = 0 To 1
    Dim OutCtl As TextBox = If(x = 0, Me.TextBox1, Me.TextBox2)
    Dim _result As Integer = Test_ParallelTasks("192.168.1.1", OutCtl)
    Await Task.Delay(1000)
    NumberOfProcesses += _result
Next

请注意，OutputDataReceived事件时会创建一个新任务处理程序报告已收到新数据。用户界面已更新相应地使用DataReceivedEventArgs e.Data。

Private Function Test_ParallelTasks(ByVal MediaToConvert As String, OutCtl As TextBox) As Integer
    Dim _processexitcode As Integer
    Dim _CurrentProcessInfo As Integer
    Dim _CurrentProcess As Integer

    Task.Factory.StartNew(Function()
        psInfoPool.Add(New ProcessStartInfo)
        _CurrentProcessInfo = psInfoPool.Count - 1
        psInfoPool(_CurrentProcessInfo).RedirectStandardOutput = True
        psInfoPool(_CurrentProcessInfo).CreateNoWindow = True
        psInfoPool(_CurrentProcessInfo).UseShellExecute = False
        psInfoPool(_CurrentProcessInfo).FileName = "Tracert"  'psInfo.FileName = ".\mycmd.exe"
        psInfoPool(_CurrentProcessInfo).Arguments = MediaToConvert
        psInfoPool(_CurrentProcessInfo).WindowStyle = ProcessWindowStyle.Hidden

        ProcessPool.Add(New Process)
        _CurrentProcess = ProcessPool.Count - 1
        ProcessPool(_CurrentProcess) = New Process() With {.StartInfo = psInfoPool(_CurrentProcessInfo),
                                                           .EnableRaisingEvents = True,
                                                           .SynchronizingObject = Me}

        ProcessPool(_CurrentProcess).Start()
        ProcessPool(_CurrentProcess).BeginOutputReadLine()

        AddHandler ProcessPool(_CurrentProcess).OutputDataReceived,
            Sub(sender As Object, e As DataReceivedEventArgs)
                If e.Data IsNot Nothing Then
                    Try
                        'Update the UI or report progress 
                        Dim UpdateUI As Task = Task.Factory.StartNew(Sub()
                        Try
                            OutCtl.AppendText(e.Data + Environment.NewLine)
                        Catch exp As Exception
                              'An exception may raise if the form is closed
                        End Try

                        End Sub, CancellationToken.None, TaskCreationOptions.PreferFairness, _Scheduler)
                        UpdateUI.Wait()

                    Catch exp As Exception
                       'Do something here
                    End Try
                End If
            End Sub

        'Add an event handler for the Exited event
        AddHandler ProcessPool(_CurrentProcess).Exited,
                Sub(source As Object, ev As EventArgs)
                    _processexitcode = ProcessPool(_CurrentProcess).ExitCode
                    Console.WriteLine("The process has exited. Code: {0}  Time: {1}",
                    _processexitcode,
                    ProcessPool(_CurrentProcess).ExitTime)
                End Sub

        ProcessPool(_CurrentProcess).WaitForExit()
        ProcessPool(_CurrentProcess).Close()
        Return _processexitcode
    End Function, TaskCreationOptions.LongRunning, CancellationToken.None)

    Return If(_processexitcode = 0, 1, 0)
End Function

在BackgroundWorker中使用Await会导致引发WorkerComplete事件

1 个答案: