当在CancelAsync()调用和RunWorkerAsync()调用之间只有非常小的间隔时,我在使用VB.net停止然后启动后台工作程序时遇到一些困难 . 我已经创建了一个示例来说明下面的问题 . 如果单击按钮一次然后快速连续单击两次,则会出现此示例中的问题 . 从本质上讲,正如我所理解的那样,问题是后台工作者仍在迭代for循环(包括模拟需要一些时间运行的代码)并且还没有机会检查取消是否正在等待 .
我试图使用的解决方案是等待后台工作程序关闭然后再次启动工作程序 . 但是,这个while循环无限循环 - 后台工作程序永远不会终止 . 我假设将主线程置于睡眠状态也会使后台工作线程进入休眠状态 . 它是否正确?
问题:什么是建议的方法来阻止后台工作人员,然后可能需要在几分之一秒后再次启动它,当检查待处理的取消时,不能比它更经常地合理地完成?
建议和评论非常感谢 .
Public Class Form1
Dim WithEvents bgWorker As System.ComponentModel.BackgroundWorker = New System.ComponentModel.BackgroundWorker
Friend WithEvents startStopButton As Button = New Button
Dim workerShouldBeRunning As Boolean = False
Sub startStopButton_click() Handles startStopButton.Click
If workerShouldBeRunning Then
bgWorker.CancelAsync()
Else
While bgWorker.IsBusy
Threading.Thread.Sleep(1)
End While
bgWorker.RunWorkerAsync()
End If
workerShouldBeRunning = Not workerShouldBeRunning
End Sub
Sub bgWorker_doWork() Handles bgWorker.DoWork
While Not bgWorker.CancellationPending
Dim sum As Long
For counter = 1 To 100000
sum += counter
Next
Threading.Thread.Sleep(1000)
End While
End Sub
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
startStopButton.Location = New Point(10, 100)
startStopButton.Size = New System.Drawing.Size(200, 23)
startStopButton.Text = "Click" 'Click to start or stop the background dummy process.
Me.Controls.Add(startStopButton)
bgWorker.WorkerSupportsCancellation = True
End Sub
End Class
编辑:
使用Ross Presser的建议,我改进了示例代码 . 但是,解决方案似乎有点差 .
Public Class Form1
Dim WithEvents bgWorker As System.ComponentModel.BackgroundWorker = New System.ComponentModel.BackgroundWorker
Friend WithEvents startStopButton As Button = New Button
Dim workerShouldBeRunning As Boolean = False
Dim startQueued As Boolean = False
Sub startStopButton_click() Handles startStopButton.Click
If workerShouldBeRunning Then
bgWorker.CancelAsync()
Else
If bgWorker.IsBusy Then
startQueued = True
Else
bgWorker.RunWorkerAsync()
End If
End If
workerShouldBeRunning = Not workerShouldBeRunning
End Sub
Sub bgWorker_doWork() Handles bgWorker.DoWork
While Not bgWorker.CancellationPending
Dim sum As Long
For counter = 1 To 100000
sum += counter
Next
Threading.Thread.Sleep(1000)
End While
End Sub
Sub bgWorkerCompleted() Handles bgWorker.RunWorkerCompleted
If startQueued Then
startQueued = False
bgWorker.RunWorkerAsync()
End If
End Sub
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
startStopButton.Location = New Point(10, 100)
startStopButton.Size = New System.Drawing.Size(200, 23)
startStopButton.Text = "Click" 'Click to start or stop the background dummy process.
Me.Controls.Add(startStopButton)
bgWorker.WorkerSupportsCancellation = True
End Sub
End Class
2 回答
而不是检查
IsBusy
,我会处理BackgroundWorker.RunWorkerCompleted
event并推迟重新启动worker到此事件的处理程序 .
这种方法怎么样?...我们只需用新的替换旧的背景工作者: