Why does Join method call sit there forever?

28 Nov 2006 5:39 AM

Dachshund Digital

Why does Join method call sit there forever? This code works,
including the delegate call, but if the join method is ever called, it
seems the main thread blocks, and it is hung. HELP! This is driving
me nuts!

-----------------------------------------------------------------------------------

Imports System
Imports System.Threading
Imports System.Environment

'

Public Class Form1

    '

    Private Delegate Sub UpdateDelegate()

    Private theThreadOrNot, theUpdateOrNot As Boolean
    Private theDelegate As UpdateDelegate
    Private theReset As ManualResetEvent
    Private theThread As Thread

    '

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As
System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing

        '

        If (theUpdateOrNot) Then

            '

            theReset.Reset()
            theUpdateOrNot = False

            Thread.Sleep(250)

        End If

        theThreadOrNot = True
        theReset.Set()

        If (theThread Is Nothing) Then

            '

            Exit Sub

        End If

        If (theThread.IsAlive) Then

            '

            theThread.Join()

        End If

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load

        '

        theReset = New ManualResetEvent(False)

        theDelegate = New UpdateDelegate(AddressOf _
            OnUpdate)

        theThread = New Thread(AddressOf _
            OnThread)

        With theThread

            '

            .IsBackground = True
            .Priority = ThreadPriority.Normal

            .Start()

        End With

    End Sub

    Private Sub OnThread()

        '

        While (Not (theThreadOrNot))

            '

            If (theReset.WaitOne) Then

                '

                While (Not theThreadOrNot And theUpdateOrNot)

                    '

                    If (Me.InvokeRequired) _
                        Then

                        '

                        Me.Invoke(theDelegate)

                    End If

                End While

            End If

        End While

    End Sub

    Private Sub OnUpdate()

        '

        Me.Label.Text = TickCount.ToString

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click

        If (theUpdateOrNot) Then

            '

            theReset.Reset()
            theUpdateOrNot = False

        Else

            '

            theReset.Set()
            theUpdateOrNot = True

        End If

    End Sub

End Class

28 Nov 2006 12:03 PM

Patrice

My first move would be to check if I actually reach the end of the thread
(you could add a trace or whatever to see if you are still looping).

--

"Dachshund Digital" <Schors***@adelphia.net> a écrit dans le message de

news: 1164692386.776672.62***@l12g2000cwl.googlegroups.com...
Show quoteHide quote

> Why does Join method call sit there forever? This code works,
> including the delegate call, but if the join method is ever called, it
> seems the main thread blocks, and it is hung. HELP! This is driving
> me nuts!
>
> -----------------------------------------------------------------------------------
>
> Imports System
> Imports System.Threading
> Imports System.Environment
>
> '
>
> Public Class Form1
>
>    '
>
>    Private Delegate Sub UpdateDelegate()
>
>    Private theThreadOrNot, theUpdateOrNot As Boolean
>    Private theDelegate As UpdateDelegate
>    Private theReset As ManualResetEvent
>    Private theThread As Thread
>
>    '
>
>    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As
> System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
>
>        '
>
>        If (theUpdateOrNot) Then
>
>            '
>
>            theReset.Reset()
>            theUpdateOrNot = False
>
>            Thread.Sleep(250)
>
>        End If
>
>        theThreadOrNot = True
>        theReset.Set()
>
>        If (theThread Is Nothing) Then
>
>            '
>
>            Exit Sub
>
>        End If
>
>        If (theThread.IsAlive) Then
>
>            '
>
>            theThread.Join()
>
>        End If
>
>    End Sub
>
>    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles MyBase.Load
>
>        '
>
>        theReset = New ManualResetEvent(False)
>
>        theDelegate = New UpdateDelegate(AddressOf _
>            OnUpdate)
>
>        theThread = New Thread(AddressOf _
>            OnThread)
>
>        With theThread
>
>            '
>
>            .IsBackground = True
>            .Priority = ThreadPriority.Normal
>
>            .Start()
>
>        End With
>
>    End Sub
>
>    Private Sub OnThread()
>
>        '
>
>        While (Not (theThreadOrNot))
>
>            '
>
>            If (theReset.WaitOne) Then
>
>                '
>
>                While (Not theThreadOrNot And theUpdateOrNot)
>
>                    '
>
>                    If (Me.InvokeRequired) _
>                        Then
>
>                        '
>
>                        Me.Invoke(theDelegate)
>
>                    End If
>
>                End While
>
>            End If
>
>        End While
>
>    End Sub
>
>    Private Sub OnUpdate()
>
>        '
>
>        Me.Label.Text = TickCount.ToString
>
>    End Sub
>
>    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>
>        If (theUpdateOrNot) Then
>
>            '
>
>            theReset.Reset()
>            theUpdateOrNot = False
>
>        Else
>
>            '
>
>            theReset.Set()
>            theUpdateOrNot = True
>
>        End If
>
>    End Sub
>
> End Class
>

30 Nov 2006 4:08 AM

Dachshund Digital

Did that... the MsgBox() method call is never done.

30 Nov 2006 5:25 AM

Dachshund Digital

I did figure out part of the problem. If I call join in the
FormClosing event, it appears the thread blocks its-self and the join
never seeing the thread complete, keeps waiting, effectively forever.

Given this new information... I found a couple of references to similar
problems .NET.

If I Disable the FormClosing event until the user explicitly clicks the
button to stop the thread processing, then enable the FormClosing event
processing, I never get Join to hang.

This has to be something with the why the FormClosing event is
implemented.

30 Nov 2006 1:54 PM

Brian Gideon

Dachshund,

This is a common deadlock scenario. The UI thread calls Join on the
worker thread, but the worker thread needs to Invoke a method on the UI
thread before it can complete. Deadlock! The UI thread is blocking on
the theThread.Join call and the worker thread is blocking on the
Me.Invoke call. It really has very little to do with the FormClosing
event specifically.

Brian

Dachshund Digital wrote:
Show quoteHide quote

> Why does Join method call sit there forever? This code works,
> including the delegate call, but if the join method is ever called, it
> seems the main thread blocks, and it is hung. HELP! This is driving
> me nuts!
>
> -----------------------------------------------------------------------------------
>
> Imports System
> Imports System.Threading
> Imports System.Environment
>
> '
>
> Public Class Form1
>
>     '
>
>     Private Delegate Sub UpdateDelegate()
>
>     Private theThreadOrNot, theUpdateOrNot As Boolean
>     Private theDelegate As UpdateDelegate
>     Private theReset As ManualResetEvent
>     Private theThread As Thread
>
>     '
>
>     Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As
> System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
>
>         '
>
>         If (theUpdateOrNot) Then
>
>             '
>
>             theReset.Reset()
>             theUpdateOrNot = False
>
>             Thread.Sleep(250)
>
>         End If
>
>         theThreadOrNot = True
>         theReset.Set()
>
>         If (theThread Is Nothing) Then
>
>             '
>
>             Exit Sub
>
>         End If
>
>         If (theThread.IsAlive) Then
>
>             '
>
>             theThread.Join()
>
>         End If
>
>     End Sub
>
>     Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles MyBase.Load
>
>         '
>
>         theReset = New ManualResetEvent(False)
>
>         theDelegate = New UpdateDelegate(AddressOf _
>             OnUpdate)
>
>         theThread = New Thread(AddressOf _
>             OnThread)
>
>         With theThread
>
>             '
>
>             .IsBackground = True
>             .Priority = ThreadPriority.Normal
>
>             .Start()
>
>         End With
>
>     End Sub
>
>     Private Sub OnThread()
>
>         '
>
>         While (Not (theThreadOrNot))
>
>             '
>
>             If (theReset.WaitOne) Then
>
>                 '
>
>                 While (Not theThreadOrNot And theUpdateOrNot)
>
>                     '
>
>                     If (Me.InvokeRequired) _
>                         Then
>
>                         '
>
>                         Me.Invoke(theDelegate)
>
>                     End If
>
>                 End While
>
>             End If
>
>         End While
>
>     End Sub
>
>     Private Sub OnUpdate()
>
>         '
>
>         Me.Label.Text = TickCount.ToString
>
>     End Sub
>
>     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>
>         If (theUpdateOrNot) Then
>
>             '
>
>             theReset.Reset()
>             theUpdateOrNot = False
>
>         Else
>
>             '
>
>             theReset.Set()
>             theUpdateOrNot = True
>
>         End If
>
>     End Sub
>
> End Class