Worker thread blocking on calls to .Invoke

I need a thread to run a subroutine which updates my main form's
progress bar. I've properly marshaled all UI updates to the main UI
thread, and after the main thread starts the worker thread, it waits
for the worker thread to complete by means of a while t.isAlive,
sleep(0) mechanism. But when my worker thread calls my
UpdateProgressBar routine, which calls Me.Invoke, the invoke call
blocks forever. But I can't figure out why the main thread never
services the invoke call.

--
Jeff S.
Here's a sample program:

Public Class Form1
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 IfPublic Class Form1
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 ProgressBar1 As System.Windows.Forms.ProgressBar
Friend WithEvents Button1 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.ProgressBar1 = New System.Windows.Forms.ProgressBar
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'ProgressBar1
'
Me.ProgressBar1.Location = New System.Drawing.Point(8, 40)
Me.ProgressBar1.Name = "ProgressBar1"
Me.ProgressBar1.TabIndex = 0
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(8, 8)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(96, 23)
Me.Button1.TabIndex = 1
Me.Button1.Text = "Go"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(112, 69)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.ProgressBar1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)
End Sub

#End Region

Dim t As Threading.Thread

Private Delegate Sub UpdateProgressDelegate(ByVal value As
Integer)

Private Sub UpdateProgress(ByVal value As Integer)
If Me.ProgressBar1.InvokeRequired Then
Dim delegateObj As UpdateProgressDelegate = New
UpdateProgressDelegate(AddressOf UpdateProgress)
Me.ProgressBar1.Invoke(delegateObj, New Object() {value})
Else
Me.ProgressBar1.Value = value
End If
End Sub
Private Sub ThreadRunner()
For i As Integer = 1 To 100
Me.UpdateProgress(i)
Threading.Thread.CurrentThread.Sleep(1000)
Next
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click
Me.t = New Threading.Thread(AddressOf ThreadRunner)
t.Start()
End Sub
End Class

Hello Jeff,

I understand what you're trying to do. Instead of trying to manipulate Windows
Form from another thread, why don't you fire an event and have the Windows
Form that's running in the main thread subscribe to it so that you won't
have the thread issue? I've done something similar to what you're trying
to accomplish and successfully done it. Please let me know if you have further
question.

On 2004-11-27, Hayato Iriumi <hi*****@hotmail.com> wrote:

Hello Jeff,

I understand what you're trying to do. Instead of trying to
manipulate Windows Form from another thread, why don't you fire an
event and have the Windows Form that's running in the main thread
subscribe to it so that you won't have the thread issue? I've done
something similar to what you're trying to accomplish and
successfully done it. Please let me know if you have further
question.

The event, if fired from a separate thread will not necessarilly be in
the forms thread. Though it may appear to work, you may in fact be
looking down the barrel of a crash :) You should check the
InvokeRequired property of the form in the event to make sure that it
is safe to directly update that form.

I need a thread to run a subroutine which updates my main form's
progress bar. I've properly marshaled all UI updates to the main UI
thread, and after the main thread starts the worker thread, it waits
for the worker thread to complete by means of a while t.isAlive,
sleep(0) mechanism.
Really? Although your example has two identical constructors, there's
no call to IsAlive in there, and no call to Sleep on the main thread.
Are there other differences between your sample code and what you
posted?

Anyway, the posted code works fine for me, although with the
ProgressBar1.Width set so small, you'll only see the bar move every 15
seconds or so, so it might seem like the Invoke isn't getting processed
unless you wait around for it.

Also, you might want to set the IsBackground property of the thread, or
have some other means of thread synchronization, otherwise the secondary
thread will hang around even after the user has closed the form.
But when my worker thread calls my UpdateProgressBar routine, which calls Me.Invoke, the invoke call
blocks forever. But I can't figure out why the main thread never
services the invoke call.

--
Jeff S.
Here's a sample program:

Public Class Form1
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 IfPublic Class Form1
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 ProgressBar1 As System.Windows.Forms.ProgressBar
Friend WithEvents Button1 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.ProgressBar1 = New System.Windows.Forms.ProgressBar
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'ProgressBar1
'
Me.ProgressBar1.Location = New System.Drawing.Point(8, 40)
Me.ProgressBar1.Name = "ProgressBar1"
Me.ProgressBar1.TabIndex = 0
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(8, 8)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(96, 23)
Me.Button1.TabIndex = 1
Me.Button1.Text = "Go"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(112, 69)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.ProgressBar1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region

Dim t As Threading.Thread

Private Delegate Sub UpdateProgressDelegate(ByVal value As
Integer)

Private Sub UpdateProgress(ByVal value As Integer)
If Me.ProgressBar1.InvokeRequired Then
Dim delegateObj As UpdateProgressDelegate = New
UpdateProgressDelegate(AddressOf UpdateProgress)
Me.ProgressBar1.Invoke(delegateObj, New Object() {value})
Else
Me.ProgressBar1.Value = value
End If
End Sub

Private Sub ThreadRunner()
For i As Integer = 1 To 100
Me.UpdateProgress(i)
Threading.Thread.CurrentThread.Sleep(1000)
Next
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click
Me.t = New Threading.Thread(AddressOf ThreadRunner)
t.Start()
End Sub
End Class

Really? Although your example has two identical constructors, there's
no call to IsAlive in there, and no call to Sleep on the main thread.
Are there other differences between your sample code and what you
posted?

I need a thread to run a subroutine which updates my main form's
progress bar. I've properly marshaled all UI updates to the main UI
thread, and after the main thread starts the worker thread, it waits
for the worker thread to complete by means of a while t.isAlive,
sleep(0) mechanism. But when my worker thread calls my
UpdateProgressBar routine, which calls Me.Invoke, the invoke call
blocks forever. But I can't figure out why the main thread never
services the invoke call.

--
Jeff S.
Here's a sample program:

Public Class Form1
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 IfPublic Class Form1
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 ProgressBar1 As System.Windows.Forms.ProgressBar
Friend WithEvents Button1 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.ProgressBar1 = New System.Windows.Forms.ProgressBar
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'ProgressBar1
'
Me.ProgressBar1.Location = New System.Drawing.Point(8, 40)
Me.ProgressBar1.Name = "ProgressBar1"
Me.ProgressBar1.TabIndex = 0
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(8, 8)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(96, 23)
Me.Button1.TabIndex = 1
Me.Button1.Text = "Go"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(112, 69)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.ProgressBar1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region

Dim t As Threading.Thread

Private Delegate Sub UpdateProgressDelegate(ByVal value As
Integer)

Private Sub UpdateProgress(ByVal value As Integer)
If Me.ProgressBar1.InvokeRequired Then
Dim delegateObj As UpdateProgressDelegate = New
UpdateProgressDelegate(AddressOf UpdateProgress)
Me.ProgressBar1.Invoke(delegateObj, New Object() {value})
Else
Me.ProgressBar1.Value = value
End If
End Sub

Private Sub ThreadRunner()
For i As Integer = 1 To 100
Me.UpdateProgress(i)
Threading.Thread.CurrentThread.Sleep(1000)
Next
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click
Me.t = New Threading.Thread(AddressOf ThreadRunner)
t.Start()
End Sub
End Class

I need a thread to run a subroutine which updates my main form's
progress bar. I've properly marshaled all UI updates to the main UI
thread, and after the main thread starts the worker thread, it waits
for the worker thread to complete by means of a while t.isAlive,
sleep(0) mechanism. But when my worker thread calls my
UpdateProgressBar routine, which calls Me.Invoke, the invoke call
blocks forever. But I can't figure out why the main thread never
services the invoke call.

--
Jeff S.
Here's a sample program:

Public Class Form1
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 IfPublic Class Form1
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 ProgressBar1 As System.Windows.Forms.ProgressBar
Friend WithEvents Button1 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.ProgressBar1 = New System.Windows.Forms.ProgressBar
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'ProgressBar1
'
Me.ProgressBar1.Location = New System.Drawing.Point(8, 40)
Me.ProgressBar1.Name = "ProgressBar1"
Me.ProgressBar1.TabIndex = 0
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(8, 8)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(96, 23)
Me.Button1.TabIndex = 1
Me.Button1.Text = "Go"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(112, 69)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.ProgressBar1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region

Dim t As Threading.Thread

Private Delegate Sub UpdateProgressDelegate(ByVal value As
Integer)

Private Sub UpdateProgress(ByVal value As Integer)
If Me.ProgressBar1.InvokeRequired Then
Dim delegateObj As UpdateProgressDelegate = New
UpdateProgressDelegate(AddressOf UpdateProgress)
Me.ProgressBar1.Invoke(delegateObj, New Object() {value})
Else
Me.ProgressBar1.Value = value
End If
End Sub

Private Sub ThreadRunner()
For i As Integer = 1 To 100
Me.UpdateProgress(i)
Threading.Thread.CurrentThread.Sleep(1000)
Next
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click
Me.t = New Threading.Thread(AddressOf ThreadRunner)
t.Start()
End Sub
End Class