How to get a variable/value out of a thread?

[NeilF]

I want to write some code to do some processing. This seems best done in a thread. But I also want some UI and general controlling passed to and from it. eg: Adding lines to a text box for general UI updating while it's running.

Now, let's assume I might have multiple threads running, so each thread can call my UpdateUI subroutine. But the problem is, at the moment my code is using a public variable UI_Msg to pass values back from each thread to the UpdateUI subroutine. This hits me as dangerous as different threads may overwrite UI_Msg at the same time.

Instead I tryied to attach a class to each thread, so each thread has its own UI_Msg property/value. When I then get to UpdateUI, I want to pluck this value out of that thread, so there's no risk of different threads overwriting each others msgs to UpdateUI.


I've attached my code example.

So all I want to do is in UpdateUI, be able to look at UI_msg from the class for the thread calling UpdateUI. eg: Obtain thread.UI_msg for example...

Imports System.Threading

Public Class MainForm
    Public UI_msg As String

    ' Used to track which thread called the UI Update function.
    Private callingThread As Integer

    ' The Delegate that is invoked by the control on the form that needs to be updated.
    Delegate Sub UIDelegate()

    Private Sub UpdateUI()
        ' If InvokeRequired is true then the call is being made on a thread other
        ' than the UI thread.
        If Label1.InvokeRequired Then
            ' Call UpdateUI by invoking a delegate with the UI control
            callingThread = System.Threading.Thread.CurrentThread.ManagedThreadId()

            Dim newDelegate As New UIDelegate(AddressOf UpdateUI)
            Label1.Invoke(newDelegate)
        Else
            Label1.AppendText(Text + "Thread " + callingThread.ToString() + ":" + UI_msg + vbCrLf)
            ' ** How can I get the UI_MSG from the thread class? **
            UI_msg = ""
            Label1.ScrollToCaret()
        End If
    End Sub

    Private Sub StartJob_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles StartJob.Click
        UI_msg = "Starting a new thread"
        UpdateUI()

        Dim JobThread As New Thread(AddressOf RunJob)
        JobThread.Start()
    End Sub

    Class JobObjClass
        Public JobCanceled As Boolean
        Public UI_Msg As String
    End Class

    Sub RunJob()
        Dim StateObj As New JobObjClass()
        StateObj.JobCanceled = False

        Dim ctr As Integer
        ctr = 0
        While (ctr < 5 And abort = False)
            System.Threading.Thread.Sleep(1000)
            ctr = ctr + 1
            UI_msg = "Count " & ctr.ToString()
            StateObj.UI_Msg = "Count " & ctr.ToString() ' ** Want to use this instead of previous line!
            UpdateUI()
        End While

        StateObj.JobCanceled = True
        UI_msg = "Ending thread"
        UpdateUI()
    End Sub


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        abort = True
    End Sub
End Class

I hope this makes sense... I'm only a week or so into Visual Basic.

[NeilF]

I think I've done it

Imports System.Threading

Public Class MainForm
    Public jobs_running As Integer
    Public abort As Boolean

    ' Used to track which thread called the UI Update function.
    Private callingThread As Integer

    ' The Delegate that is invoked by the control on the form that needs to be updated.
    Delegate Sub UIDelegate(ByVal StatusMessage As String)


    Sub UpdateUI(ByVal Message As String)
        ' If InvokeRequired is true then the call is being made on a thread other
        ' than the UI thread.
        If Label1.InvokeRequired Then
            ' Call UpdateUI by invoking a delegate with the UI control
            callingThread = System.Threading.Thread.CurrentThread.ManagedThreadId()

            Dim newDelegate As New UIDelegate(AddressOf UpdateUI)
            Dim args() As Object = {Message}
            Label1.Invoke(newDelegate, args)
        Else
            Label1.AppendText(Text + "Thread " + callingThread.ToString() + ":" + Message + vbCrLf)
            ' ** How can I get the UI_MSG from the thread class? **
            Label1.ScrollToCaret()
            Label2.Text = jobs_running.ToString()
        End If
    End Sub

    Private Sub StartJob_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles StartJob.Click
        jobs_running = jobs_running + 1
        UpdateUI("Starting a New Thread")

        Dim JobThread As New Thread(AddressOf RunJob)
        JobThread.Start()
    End Sub

    Sub RunJob()
        Dim ctr As Integer
        ctr = 0
        While (ctr < 5 And abort = False)
            System.Threading.Thread.Sleep(1000)
            ctr = ctr + 1
            UpdateUI("Count " & ctr.ToString())
        End While

        jobs_running = jobs_running - 1
        UpdateUI("Ending Thread")
    End Sub

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

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

    End Sub
End Class

[TCarter]

I normally use a backgroundworker for threading...

Backgroundworkers can NOT update a control in the dowork function, but CAN in the report/completed functions.

So it, requires a bit of ingenuity to get it to all function.

i am glad you think you figured it out, as i didnt really look at your code. Its always nice to see people figure things out on their own, as thats how learning works

[NeilF]

I normally use a backgroundworker for threading...

Backgroundworkers can NOT update a control in the dowork function, but CAN in the report/completed functions.

So it, requires a bit of ingenuity to get it to all function.

i am glad you think you figured it out, as i didnt really look at your code. Its always nice to see people figure things out on their own, as thats how learning works

I sort of get what it's doing, but I've patched it togethor from examples and guess work, so I don't pretend to fully understand it... Especially the Delegate stuff

Just wish I had an answer to this problem - http://www.vbforums.com/showthread.php?t=616099#18

[techgnome]

A delegate is a pointer to a function. Think of it as an address on an envelope. Or a telephone number... you can't talk to you friend because he's on a different thread from you (his house vs your house) ... so you dial him up using a delegate (the phone) .. the phone acts like a proxy between your thread and your friend's thread, allowing communication (via phone wired or even cell phone towers).

What you have there should work... it looks like you've set it up correctly.

the InvokeRequired is like you yelling "Hey Buddy!" in your house... if he's not there (since he's at home), you have to go through your delegate (the phone) ... where it then gets routed around until it gets to your friend and he gets the message.

it's a messy example, but I think it illustrates the concepts at least.

-tg

[dbasnett]

    Dim go As Long = 0
    Dim ct As Long = 0
    Dim lock As New Object
    Dim running As Long
    Const _toRun As Integer = 20 'try different numbers

    Private Sub Button2_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles Button2.Click
        Button2.Enabled = False
        Label1.Text = DateTime.Now.ToLongTimeString 'set up
        Threading.Interlocked.Exchange(go, 0L)
        Threading.Interlocked.Exchange(ct, 0L)
        Threading.Interlocked.Exchange(running, 0)
        For x As Integer = 1 To _toRun 'start some threads
            Dim t As New Threading.Thread(AddressOf foo)
            t.Start()
            Threading.Thread.Sleep(10) 'give each one a chance to start
        Next
        Do 'wait for all to start
            Threading.Thread.Sleep(10)
        Loop While _toRun <> Threading.Interlocked.Read(running)

        Button3.Enabled = True
        Threading.Interlocked.Exchange(go, 1L) 'GO!
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles Button3.Click
        Threading.Interlocked.Exchange(go, 0L) 'STOP
        Button3.Enabled = False
        aTimer.Interval = 100
        aTimer.Start()
    End Sub

    Dim WithEvents aTimer As New Timer()

    Private Sub _Tick(ByVal sender As System.Object, _
                            ByVal e As System.EventArgs) Handles aTimer.Tick
        If Threading.Interlocked.Read(running) > 0 Then Exit Sub
        aTimer.Stop()
        Label1.Text = DateTime.Now.ToLongTimeString
        Button2.Enabled = True
    End Sub

    Private Sub foo()
        Dim myID As Long = Threading.Interlocked.Increment(ct) 'get myID
        Threading.Interlocked.Increment(running)
        'wait for all threads to be started
        Do While Threading.Interlocked.Read(go) = 0L
            Threading.Thread.Sleep(10) 'sleep if not
        Loop
        Do
            Threading.Monitor.Enter(lock) 'lock
            updUI(myID) 'update the UI passing in myID <<< Update UI
            Threading.Monitor.Exit(lock) 'unlock
            Threading.Thread.Sleep(100) 'comment this out and see the difference
        Loop While Threading.Interlocked.Read(go) = 1L
        Threading.Interlocked.Decrement(running)
    End Sub

    Delegate Sub Stub(ByVal aCount As Long)
    Public myDelegate As Stub

    Private Sub updUI(ByVal theCount As Long)
        If Label1.InvokeRequired Then 'on UI thread
            myDelegate = New Stub(AddressOf updUI) 'no
            Label1.Invoke(myDelegate, theCount) 'this will run on the UI
            Exit Sub
        End If
        Dim s As String = Space(CInt(theCount)) & CLng(theCount).ToString
        Label1.Text = s
        Label1.Refresh()
    End Sub

[NeilF]

    Dim go As Long = 0
    Dim ct As Long = 0
    Dim lock As New Object
    Dim running As Long
    Const _toRun As Integer = 20 'try different numbers

    Private Sub Button2_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles Button2.Click
        Button2.Enabled = False
        Label1.Text = DateTime.Now.ToLongTimeString 'set up
        Threading.Interlocked.Exchange(go, 0L)
        Threading.Interlocked.Exchange(ct, 0L)
        Threading.Interlocked.Exchange(running, 0)
        For x As Integer = 1 To _toRun 'start some threads
            Dim t As New Threading.Thread(AddressOf foo)
            t.Start()
            Threading.Thread.Sleep(10) 'give each one a chance to start
        Next
        Do 'wait for all to start
            Threading.Thread.Sleep(10)
        Loop While _toRun <> Threading.Interlocked.Read(running)

        Button3.Enabled = True
        Threading.Interlocked.Exchange(go, 1L) 'GO!
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles Button3.Click
        Threading.Interlocked.Exchange(go, 0L) 'STOP
        Button3.Enabled = False
        aTimer.Interval = 100
        aTimer.Start()
    End Sub

    Dim WithEvents aTimer As New Timer()

    Private Sub _Tick(ByVal sender As System.Object, _
                            ByVal e As System.EventArgs) Handles aTimer.Tick
        If Threading.Interlocked.Read(running) > 0 Then Exit Sub
        aTimer.Stop()
        Label1.Text = DateTime.Now.ToLongTimeString
        Button2.Enabled = True
    End Sub

    Private Sub foo()
        Dim myID As Long = Threading.Interlocked.Increment(ct) 'get myID
        Threading.Interlocked.Increment(running)
        'wait for all threads to be started
        Do While Threading.Interlocked.Read(go) = 0L
            Threading.Thread.Sleep(10) 'sleep if not
        Loop
        Do
            Threading.Monitor.Enter(lock) 'lock
            updUI(myID) 'update the UI passing in myID <<< Update UI
            Threading.Monitor.Exit(lock) 'unlock
            Threading.Thread.Sleep(100) 'comment this out and see the difference
        Loop While Threading.Interlocked.Read(go) = 1L
        Threading.Interlocked.Decrement(running)
    End Sub

    Delegate Sub Stub(ByVal aCount As Long)
    Public myDelegate As Stub

    Private Sub updUI(ByVal theCount As Long)
        If Label1.InvokeRequired Then 'on UI thread
            myDelegate = New Stub(AddressOf updUI) 'no
            Label1.Invoke(myDelegate, theCount) 'this will run on the UI
            Exit Sub
        End If
        Dim s As String = Space(CInt(theCount)) & CLng(theCount).ToString
        Label1.Text = s
        Label1.Refresh()
    End Sub

Are you able to explain:-
Threading.Interlocked.Read
Threading.Monitor.Enter
Threading.Monitor.Exit

With my previous example, all my threads would run in parallel. How does the above example work? It seems at the very least to lock around the UI updating?

[dbasnett]

Are you able to explain:-
Threading.Interlocked.Read
Threading.Monitor.Enter
Threading.Monitor.Exit

With my previous example, all my threads would run in parallel. How does the above example work? It seems at the very least to lock around the UI updating?

I can, can you Threading Link


"It seems at the very least to lock around the UI updating?" Wasn't your post about having multiple threads updating the UI? That is what it does.