【发布时间】：2014-11-13 16:19:05
【问题描述】：
基本上我正在异步启动Process，我正在等待Process 使用Task 退出，下面的代码没有任何问题，但我发现了一点我想了解的问题...
问题是，如果我使用 process.WaitForExit() 方法并尝试取消 Task （或者相同的方法，杀死进程），那么进程永远不会退出，因此子线程将永远挂起，而不是如果我使用 process.WaitForExit(Integer.MaxValue) 方法，一切都会完美。
为什么会这样？，有什么区别导致进程无法识别进程已经退出？。
Process 实例：
''' <summary>
''' The CMD <see cref="System.Diagnostics.Process"/> instance.
''' </summary>
Private WithEvents cmdProcess As New Process With
{
.EnableRaisingEvents = True,
.StartInfo = New ProcessStartInfo With
{
.FileName = "cmd.exe",
.Arguments = String.Empty,
.RedirectStandardInput = False,
.RedirectStandardOutput = True,
.RedirectStandardError = True,
.UseShellExecute = False,
.CreateNoWindow = True
}
}
Task 初始化器：
Private Sub StartTask()
Me.cmdTask = Task.Factory.StartNew(AddressOf CMDAutomate)
Me.cmdTaskCTS = New Threading.CancellationTokenSource
Me.cmdTaskCT = cmdTaskCTS.Token
End Sub
Task 所做的工作：
Private Sub CMDAutomate()
With Me.cmdProcess
.StartInfo.Arguments = String.Format("/C ""{0}""", Me.PingArguments)
.Start()
.BeginOutputReadLine()
.BeginErrorReadLine()
.WaitForExit(Integer.MaxValue)
End With
End Sub
还有Task 取消器：
Private Sub CancelTask()
If Not Me.cmdProcess.HasExited Then
With Me.cmdProcess
.CancelOutputRead()
.CancelErrorRead()
.Kill() ' kill process (cmd.exe)
End With
' cancel the task.
Me.cmdTaskCTS.Cancel()
' wait for the task cancellation finishes.
Me.cmdTask.Wait()
End If
End Sub
如果需要，这是整个代码：
Imports System.Threading
Imports System.Threading.Tasks
Public Class Form1
Private cmdTask As Task
Private cmdTaskCTS As New CancellationTokenSource
Private cmdTaskCT As CancellationToken
''' <summary>
''' The CMD <see cref="System.Diagnostics.Process"/> instance.
''' </summary>
Private WithEvents cmdProcess As New Process With
{
.EnableRaisingEvents = True,
.StartInfo = New ProcessStartInfo With
{
.FileName = "cmd.exe",
.Arguments = String.Empty,
.RedirectStandardInput = False,
.RedirectStandardOutput = True,
.RedirectStandardError = True,
.UseShellExecute = False,
.CreateNoWindow = True
}
}
''' <summary>
''' Gets the ping commandline arguments.
''' </summary>
Private ReadOnly Property PingArguments As String
Get
Return String.Format("ping.exe -t ""{0}.{1}.{2}.{3}""",
TextBox1.Text, TextBox2.Text,
TextBox3.Text, TextBox4.Text)
End Get
End Property
Private Sub btnSend_Click(ByVal sender As Object, ByVal e As EventArgs) _
Handles btnsend.Click
Me.StartTask()
End Sub
Private Sub CMDAutomate()
With Me.cmdProcess
.StartInfo.Arguments = String.Format("/C ""{0}""", Me.PingArguments)
.Start()
.BeginOutputReadLine()
.BeginErrorReadLine()
.WaitForExit(Integer.MaxValue)
End With
End Sub
''' <summary>
''' Occurs when an application writes to its redirected <see cref="System.Diagnostics.Process.StandardOutput"/> stream.
''' Occurs when an application writes to its redirected <see cref="System.Diagnostics.Process.StandardError"/> stream.
''' </summary>
Private Sub cmdProcess_OutputDataReceived(ByVal sender As Object, ByVal e As DataReceivedEventArgs) _
Handles cmdProcess.OutputDataReceived,
cmdProcess.ErrorDataReceived
Select Case txtresults.InvokeRequired
Case True
txtresults.Invoke(Sub() txtresults.AppendText("" & e.Data))
txtresults.Invoke(Sub() txtresults.AppendText(Environment.NewLine))
Case Else
txtresults.AppendText(e.Data)
txtresults.AppendText(Environment.NewLine)
End Select
#If DEBUG Then
' Debug.WriteLine(e.Data)
#End If
End Sub
''' <summary>
''' Occurs when a <see cref="System.Diagnostics.Process"/> exits.
''' </summary>
Private Sub cmdProcess_Exited(ByVal sender As Object, ByVal e As EventArgs) _
Handles cmdProcess.Exited
Debug.WriteLine(String.Format("cmdProcess has exited with exit code: {0}",
DirectCast(sender, Process).ExitCode))
End Sub
Private Sub LinkLabel1_LinkClicked(sender As Object, e As LinkLabelLinkClickedEventArgs) _
Handles LinkLabel1.LinkClicked
' limpio el texto de cada textbox.
For Each tb As TextBox In Me.Controls.OfType(Of TextBox)()
tb.Clear()
Next tb
' cancelo la tarea en segundo plano.
Me.CancelTask()
End Sub
Private Sub StartTask()
Me.cmdTask = Task.Factory.StartNew(AddressOf CMDAutomate)
Me.cmdTaskCTS = New Threading.CancellationTokenSource
Me.cmdTaskCT = cmdTaskCTS.Token
End Sub
Private Sub CancelTask()
' Si el proceso no se ha detenido...
If Not Me.cmdProcess.HasExited Then
With Me.cmdProcess
' cancelo la lectura de los outputs.
.CancelOutputRead()
.CancelErrorRead()
.Kill() ' mato el proceso (cmd.exe)
End With
' Cancelo la tarea en segundo plano.
Me.cmdTaskCTS.Cancel()
' Espero a que la tarea se haya cancelado.
Me.cmdTask.Wait()
End If
End Sub
End Class
【问题讨论】：
-
尝试设置 Process.SynchronizingObject：msdn.microsoft.com/en-us/library/…
标签： .net vb.net multithreading asynchronous process