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Gracefully suspending / stopping a thread

Posted on 2009-07-09
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Last Modified: 2012-05-07
Hi
I have just now learning about threads.  
Here is what I want do to......   I wish to create a thread and "Start" it.

I want to be able to suspend it (and later use it again) in my application.
I also wold like to destroy it as I close my application.

Of course,  I would like to do this gracefully.

I would appreciate a short demo.

Thanks
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Question by:peispud
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Expert Comment

by:Tapan Pattanaik
ID: 24820444
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LVL 85

Accepted Solution

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Mike Tomlinson earned 500 total points
ID: 24820464
You can't really suspend a thread at any given time...you have to pick discrete points in the thread loop/code where YOU check some kind of flag and then put the thread into a waiting state.  One way to accomplish this is with a ManualResetEvent.

Here is an example using a simple "clock thread"...add a Label and two Buttons to a blank form:
Public Class Form1
 
    Private WithEvents clk As Clock
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        clk = New Clock
    End Sub
 
    Private Sub clk_CurrentTime(ByVal dt As Date) Handles clk.CurrentTime
        Label1.Text = dt.ToString
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        clk.SuspendThread()
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        clk.ResumeThread()
    End Sub
 
    Private Class Clock
 
        Private Suspend As Boolean = False
        Private T As System.Threading.Thread
        Public Event CurrentTime(ByVal dt As DateTime)
        Private SC As System.Threading.SynchronizationContext
        Private MRE As New System.Threading.ManualResetEvent(False)
 
        Public Sub New()
            SC = System.Windows.Forms.WindowsFormsSynchronizationContext.Current
            T = New System.Threading.Thread(AddressOf TickTock)
            T.IsBackground = True ' <-- allow thread to be killed automatically when app closes
            T.Start()
        End Sub
 
        Private Sub TickTock()
            While True
                System.Threading.Thread.Sleep(1000)
                SC.Post(New System.Threading.SendOrPostCallback(AddressOf TimeHack), DateTime.Now)
 
                If Suspend Then
                    MRE.Reset()
                    MRE.WaitOne() ' will STOP and WAIT here until MRE is signaled w/ the Set() method
                    Suspend = False
                End If
            End While
        End Sub
 
        Private Sub TimeHack(ByVal state As Object)
            RaiseEvent CurrentTime(state)
        End Sub
 
        Public Sub SuspendThread()
            Suspend = True
        End Sub
 
        Public Sub ResumeThread()
            MRE.Set()
        End Sub
 
    End Class
 
End Class

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Author Closing Comment

by:peispud
ID: 31601930
Thank you very much!!  I will have to think through your response,  but you have answered my question perfectly.  Much appreciated!!
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LVL 85

Expert Comment

by:Mike Tomlinson
ID: 24828450
Glad it was helpful.  I understand that's a lot to take in...feel free to ask any questions about it and I'll do my best to answer them.  =)
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