"Don" <D**@discussions.microsoft.com> wrote in message
news:B71E1C98-EB63-486E-AA86-1DF9DD0123A9@microsoft.com...
> How to stop a process which is running in a separate thread!!!
>
> I've got a class which performs some lengthy process in a background
> (separate) thread. And this lengthy process raises events regularly to
> inform
> the main thread of the progress (which is then displayed to the user).
> Since the event is raised from another thread, i've used me.Invoke() to
> update the ui properly.
>
> However, my problem is in cancelling the process.
> I need to be able to execute a method such as Cancel() which will return
> only when the process has been cancelled.
> Below is the code i've implemented.
>
> How ever, the WaitOne() method will ALWAYS return FALSE.
> I'm assuming this is becuase the WaitOne causes the current thread to wait
> untill it receives a signal. & since the current thread is also in the
> process of updating the UI, the background process thread is not able to
> send
> the signal.
> Hence a dead lock (if not for the timeout in the WaitOne())
>
> I'm sure this HAS to be possible.
> I need a mechanism to cancel the background process and WAIT till it
> confirms that the process has been cancelled (i.e. wait till the process
> notifies the main thread that the process has been cancelled).
>
> How can this be done?
>
> Below is a sample the code which outlies the above issue:
>
>
> Public Class frmThreads
>    Inherits System.Windows.Forms.Form
>
> #Region " Windows Form Designer generated code "
>
>    Public Sub New()
>        MyBase.New()
>
>        'This call is required by the Windows Form Designer.
>        InitializeComponent()
>
>        'Add any initialization after the InitializeComponent() call
>
>    End Sub
>
>    'Form overrides dispose to clean up the component list.
>    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
>        If disposing Then
>            If Not (components Is Nothing) Then
>                components.Dispose()
>            End If
>        End If
>        MyBase.Dispose(disposing)
>    End Sub
>
>    'Required by the Windows Form Designer
>    Private components As System.ComponentModel.IContainer
>
>    'NOTE: The following procedure is required by the Windows Form Designer
>    'It can be modified using the Windows Form Designer.
>    'Do not modify it using the code editor.
>    Friend WithEvents Button1 As System.Windows.Forms.Button
>    Friend WithEvents Button2 As System.Windows.Forms.Button
>    Friend WithEvents Label1 As System.Windows.Forms.Label
>    <System.Diagnostics.DebuggerStepThrough()> Private Sub
> InitializeComponent()
>        Me.Button1 = New System.Windows.Forms.Button
>        Me.Button2 = New System.Windows.Forms.Button
>        Me.Label1 = New System.Windows.Forms.Label
>        Me.SuspendLayout()
>        '
>        'Button1
>        '
>        Me.Button1.Location = New System.Drawing.Point(40, 120)
>        Me.Button1.Name = "Button1"
>        Me.Button1.TabIndex = 0
>        Me.Button1.Text = "Button1"
>        '
>        'Button2
>        '
>        Me.Button2.Location = New System.Drawing.Point(128, 120)
>        Me.Button2.Name = "Button2"
>        Me.Button2.TabIndex = 1
>        Me.Button2.Text = "Button2"
>        '
>        'Label1
>        '
>        Me.Label1.Location = New System.Drawing.Point(32, 24)
>        Me.Label1.Name = "Label1"
>        Me.Label1.TabIndex = 2
>        Me.Label1.Text = "Label1"
>        '
>        'frmThreads
>        '
>        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
>        Me.ClientSize = New System.Drawing.Size(292, 266)
>        Me.Controls.Add(Me.Label1)
>        Me.Controls.Add(Me.Button2)
>        Me.Controls.Add(Me.Button1)
>        Me.Name = "frmThreads"
>        Me.Text = "frmThreads"
>        Me.ResumeLayout(False)
>
>    End Sub
>
> #End Region
>
>    Private _lengthyProcess As LengthyProcess
>    Private _counter As Integer
>    Private dlgIvokeProgress As New dlgProgress(AddressOf ShowProgress)
>
>    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>        _lengthyProcess = New LengthyProcess
>        AddHandler _lengthyProcess.Progress, AddressOf
> LengthyProcess_Progress
>
>        Dim start As New Threading.Thread(AddressOf StartProcess)
>        start.Start()
>    End Sub
>
>    Private Sub StartProcess()
>        _lengthyProcess.Start()
>    End Sub
>
>    Private Sub LengthyProcess_Progress(ByVal counter As Integer)
>        _counter = counter
>        Me.Invoke(dlgIvokeProgress)
>    End Sub
>
>    Private Delegate Sub dlgProgress()
>    Private Sub ShowProgress()
>        Me.Label1.Text = _counter
>    End Sub
>
>    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button2.Click
>        MsgBox(_lengthyProcess.Cancel)
>    End Sub
> End Class
>
> Public Class LengthyProcess
>
>    Public Event Progress(ByVal counter As Integer)
>
>    Private _counter As Integer
>    Private _cancelled As Boolean
>    Private _stopped As Threading.ManualResetEvent
>
>    Public Sub Start()
>        Do While _cancelled = False
>            _counter += 1
>
>            Threading.Thread.Sleep(100)
>            RaiseEvent Progress(_counter)
>        Loop
>
>        If _cancelled = True Then
>            _stopped.Set()
>        End If
>    End Sub
>
>    Public Function Cancel() As Boolean
>        _stopped = New Threading.ManualResetEvent(False)
>        _cancelled = True
>
>
>        'this will ALWAYS return FALSE
>        'how ever if i were to display a messagebox here and THEN
>        'execute the WaitOne(), it will return TRUE
>        'MsgBox("WaitOne will now return TRUE")
>
>        Return _stopped.WaitOne(5000, False)
>    End Function
> End Class

"Stephany Young" wrote:

> I think that you've tried to over-engineer it a tad and in the process have
> confused yourself. Try this very simple code and then take it from there:
>
> Note that the thread is now completely encapsulated within the
> LengthyProcess class and the calling process does not need to know anything
> about the thread. It only needs to know that the LengthyProcess class has a
> Start method, a Cancel method and raises a Progress event.
>
> In the LengthyProcess.Cancel method the call to _process.Join() has the
> effect of waiting until the thread has actually finished which should be
> somewhere up to 100 milliseconds plus the overhead for raising the Progress
> event after the _cancel variable is set.
>
> Also note that your UI thread (the form) will block each time the Progress
> event is raised for as long at it takes to execute the ShowProgress method.
> This means that ShowProgress must be as lean and mean as you can make it. As
> an alternatively you could use BeginInvoke instead of Invoke which has the
> effect of sending the ShowProgress method off to do it's stuff and
> immediately allowing the LengthyProcess thread to continue.
>
> <snip>all the preamble</snip
>
>   Private _lengthyProcess As LengthyProcess
>   Private _counter As Integer
>   Private Delegate Sub dlgProgress()
>   Private dlgIvokeProgress As New dlgProgress(AddressOf ShowProgress)
>
>   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>     _lengthyProcess = New LengthyProcess
>     AddHandler _lengthyProcess.Progress, AddressOf LengthyProcess_Progress
>     _lengthyProcess.Start()
>   End Sub
>
>   Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button2.Click
>     _lengthyProcess.Cancel
>   End Sub
>
>   Private Sub LengthyProcess_Progress(ByVal counter As Integer)
>     _counter = counter
>     Invoke(dlgIvokeProgress)
>   End Sub
>
>   Private Sub ShowProgress()
>     Label1.Text = _counter.ToString()
>     Label1.Update()
>   End Sub
>
> End Class
>
> Public Class LengthyProcess
>
>   Public Event Progress(ByVal counter As Integer)
>   Private _counter As Integer = 0
>   Private _process as Thread = Nothing
>   Private _cancel as Boolean = False
>
>   Public Sub Start()
>     _process = New Thread(AddressOf TheProcess)
>     _process.Start()
>   End Sub
>
>   Public Sub Cancel()
>     _cancel = True
>     _process.Join()
>   End Sub
>
>   Private Sub TheProcess()
>     While Not _cancel
>       _counter += 1
>       Thread.Sleep(100)
>       RaiseEvent Progress(_counter)
>     End While
>   End Sub
>
> End Class
>
>
> "Don" <D**@discussions.microsoft.com> wrote in message
> news:B71E1C98-EB63-486E-AA86-1DF9DD0123A9@microsoft.com...
> > How to stop a process which is running in a separate thread!!!
> >
> > I've got a class which performs some lengthy process in a background
> > (separate) thread. And this lengthy process raises events regularly to
> > inform
> > the main thread of the progress (which is then displayed to the user).
> > Since the event is raised from another thread, i've used me.Invoke() to
> > update the ui properly.
> >
> > However, my problem is in cancelling the process.
> > I need to be able to execute a method such as Cancel() which will return
> > only when the process has been cancelled.
> > Below is the code i've implemented.
> >
> > How ever, the WaitOne() method will ALWAYS return FALSE.
> > I'm assuming this is becuase the WaitOne causes the current thread to wait
> > untill it receives a signal. & since the current thread is also in the
> > process of updating the UI, the background process thread is not able to
> > send
> > the signal.
> > Hence a dead lock (if not for the timeout in the WaitOne())
> >
> > I'm sure this HAS to be possible.
> > I need a mechanism to cancel the background process and WAIT till it
> > confirms that the process has been cancelled (i.e. wait till the process
> > notifies the main thread that the process has been cancelled).
> >
> > How can this be done?
> >
> > Below is a sample the code which outlies the above issue:
> >
> >
> > Public Class frmThreads
> >    Inherits System.Windows.Forms.Form
> >
> > #Region " Windows Form Designer generated code "
> >
> >    Public Sub New()
> >        MyBase.New()
> >
> >        'This call is required by the Windows Form Designer.
> >        InitializeComponent()
> >
> >        'Add any initialization after the InitializeComponent() call
> >
> >    End Sub
> >
> >    'Form overrides dispose to clean up the component list.
> >    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
> >        If disposing Then
> >            If Not (components Is Nothing) Then
> >                components.Dispose()
> >            End If
> >        End If
> >        MyBase.Dispose(disposing)
> >    End Sub
> >
> >    'Required by the Windows Form Designer
> >    Private components As System.ComponentModel.IContainer
> >
> >    'NOTE: The following procedure is required by the Windows Form Designer
> >    'It can be modified using the Windows Form Designer.
> >    'Do not modify it using the code editor.
> >    Friend WithEvents Button1 As System.Windows.Forms.Button
> >    Friend WithEvents Button2 As System.Windows.Forms.Button
> >    Friend WithEvents Label1 As System.Windows.Forms.Label
> >    <System.Diagnostics.DebuggerStepThrough()> Private Sub
> > InitializeComponent()
> >        Me.Button1 = New System.Windows.Forms.Button
> >        Me.Button2 = New System.Windows.Forms.Button
> >        Me.Label1 = New System.Windows.Forms.Label
> >        Me.SuspendLayout()
> >        '
> >        'Button1
> >        '
> >        Me.Button1.Location = New System.Drawing.Point(40, 120)
> >        Me.Button1.Name = "Button1"
> >        Me.Button1.TabIndex = 0
> >        Me.Button1.Text = "Button1"
> >        '
> >        'Button2
> >        '
> >        Me.Button2.Location = New System.Drawing.Point(128, 120)
> >        Me.Button2.Name = "Button2"
> >        Me.Button2.TabIndex = 1
> >        Me.Button2.Text = "Button2"
> >        '
> >        'Label1
> >        '
> >        Me.Label1.Location = New System.Drawing.Point(32, 24)
> >        Me.Label1.Name = "Label1"
> >        Me.Label1.TabIndex = 2
> >        Me.Label1.Text = "Label1"
> >        '
> >        'frmThreads
> >        '
> >        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
> >        Me.ClientSize = New System.Drawing.Size(292, 266)
> >        Me.Controls.Add(Me.Label1)
> >        Me.Controls.Add(Me.Button2)
> >        Me.Controls.Add(Me.Button1)
> >        Me.Name = "frmThreads"
> >        Me.Text = "frmThreads"
> >        Me.ResumeLayout(False)
> >
> >    End Sub
> >
> > #End Region
> >
> >    Private _lengthyProcess As LengthyProcess
> >    Private _counter As Integer
> >    Private dlgIvokeProgress As New dlgProgress(AddressOf ShowProgress)
> >
> >    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> > System.EventArgs) Handles Button1.Click
> >        _lengthyProcess = New LengthyProcess
> >        AddHandler _lengthyProcess.Progress, AddressOf
> > LengthyProcess_Progress
> >
> >        Dim start As New Threading.Thread(AddressOf StartProcess)
> >        start.Start()
> >    End Sub
> >
> >    Private Sub StartProcess()
> >        _lengthyProcess.Start()
> >    End Sub
> >
> >    Private Sub LengthyProcess_Progress(ByVal counter As Integer)
> >        _counter = counter
> >        Me.Invoke(dlgIvokeProgress)
> >    End Sub
> >
> >    Private Delegate Sub dlgProgress()
> >    Private Sub ShowProgress()
> >        Me.Label1.Text = _counter
> >    End Sub
> >
> >    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
> > System.EventArgs) Handles Button2.Click
> >        MsgBox(_lengthyProcess.Cancel)
> >    End Sub
> > End Class
> >
> > Public Class LengthyProcess
> >
> >    Public Event Progress(ByVal counter As Integer)
> >
> >    Private _counter As Integer
> >    Private _cancelled As Boolean
> >    Private _stopped As Threading.ManualResetEvent
> >
> >    Public Sub Start()
> >        Do While _cancelled = False
> >            _counter += 1
> >
> >            Threading.Thread.Sleep(100)
> >            RaiseEvent Progress(_counter)
> >        Loop
> >
> >        If _cancelled = True Then
> >            _stopped.Set()
> >        End If
> >    End Sub
> >
> >    Public Function Cancel() As Boolean
> >        _stopped = New Threading.ManualResetEvent(False)
> >        _cancelled = True
> >
> >
> >        'this will ALWAYS return FALSE
> >        'how ever if i were to display a messagebox here and THEN
> >        'execute the WaitOne(), it will return TRUE
> >        'MsgBox("WaitOne will now return TRUE")
> >
> >        Return _stopped.WaitOne(5000, False)
> >    End Function
> > End Class
>
>
>