Detecting hanging thread and abort it

[FrankZA]

I am working on a project where I make use of the lp_solve 5.5.0.13 DLL to solve many integer programming (IP) problems in succession. I set the timeout to 1s in order to speed up the calculations. Sometimes the solving procedure hangs.

In order to account for this I would like to start the call to the DLL to solve the IP in a new thread. That is easy. I would like to kill the thread if it hangs in order to make my program more robust. I would like to do so by timing the thread. If the thread is still active after, say 2s (1s more than my timeout limit), I would like to abort it and continue with the remaining calculations.

How should I go about doing this without waiting 2s for the threads that do not hang? The current threat should also not continue until the new thread (calculating the IP) is closed. How do I do this?

[GremlinSA]

This is one way that i can think of doing it..

For each new thread that you spawn, simply start a 2000ms timer for it, if the timer tick's and the thread is still running,kill it..

On the Fly code:

    Public WithEvents ThreadTimer As Windows.Forms.Timer

    Public Sub CallCalkThread()
        ThreadTimer = New Windows.Forms.Timer
        'Start thread
        ThreadTimer.Interval = 2000
        ThreadTimer.Enabled = True
        'do other stuff..
    End Sub

    Private Sub ThreadTimer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles ThreadTimer.Tick
        'if thread still running .. then kill thread.
    End Sub

Hope this helps...

Gremmy.

[FrankZA]

Thanks Gremlin, I appreciate the help. Will try it.

[FrankZA]

I tried the following code, but it does not abort the thread when it should. Any ideas why?

I created a simple form in SharpDevelop with a button and added this code:

Option Explicit On
Option Strict On

Imports System.Threading

Public Partial Class MainForm
	
	
	Public Sub New()
		' The Me.InitializeComponent call is required for Windows Forms designer support.
		Me.InitializeComponent()
	End Sub


	Private WithEvents ThreadTimer As New System.Windows.Forms.Timer()
	Private Shared ExitFlag As Boolean = False
	Private Shared t As Threading.Thread
	Private Shared Aborted as Boolean


	Sub ButtonClick(sender As Object, e As EventArgs)
		ExitFlag = False
		Aborted = False

		t = new Thread(AddressOf PauseThread)
		ThreadTimer.Interval = 2000
		ThreadTimer.Start()
		t.Start()

		Do While ExitFlag = False
		Loop

		If t.IsAlive Then
			t.Abort()
		End If
		
		If Aborted Then
			MsgBox("Program aborted correctly")
		Else
			MsgBox("Completed the task without aborting")
		End If
		
	End Sub
	

	Private Sub PauseThread()
		t.Sleep(5000)
		ExitFlag = True
	End Sub


	Private Sub ThreadTimer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) handles ThreadTimer.Tick
		If t.IsAlive Then
			t.Abort()
			Aborted = True
		End If
		ExitFlag = True
	End Sub
	
	
End Class

Is the while ExitFlag = False loop the best way to force the subroutine to wait for the other thread to complete?

[FrankZA]

Here is the VB.NET project that performs this test.

[dglienna]

Where are you setting the Exit condition? That should be in the Timer event, when the count is up.

[FrankZA]

Where are you setting the Exit condition? That should be in the Timer event, when the count is up.

Sorry, I'm not sure what you mean. I assume that when the time (2000ms) is up it triggers the ThreadTimer.Tick event. When this happens an if-statement checks whether or not the thread is still running. If the thread is still running it is aborted (I assume this is the correct method of killing a thread).

The ExitFlag boolean then makes a note that the thread has completed its task and the other subroutine may continue with the calculations.

Is the t.IsAlive call the correct method of checking whether or not a thread is running? Even so, if I add a breakpoint in the subroutine that is supposed to trigger after 2s, the program never seems to get there.

What's wrong here?

[FrankZA]

Ah ha! I have managed to find a way to do what I need using the Thread.Join method. Below is the code:

Option Explicit On
Option Strict On

Imports System.Threading

Public Partial Class MainForm
	
	
	Public Sub New()
		' The Me.InitializeComponent call is required for Windows Forms designer support.
		Me.InitializeComponent()
	End Sub


	Private Shared ExitFlag As Boolean = False
	Private Shared t As Threading.Thread
	Private Shared Aborted as Boolean


	Sub ButtonClick(sender As Object, e As EventArgs)
		ExitFlag = False
		Aborted = False

		t = new Thread(AddressOf PauseThread)
		t.Start()
		
		Do While ExitFlag = False
			If Not t.Join(2000) Then
				ExitFlag = True
				t.Abort()
				Aborted = True
			End If
		Loop

		If Aborted Then
			MsgBox("Program aborted correctly")
		Else
			MsgBox("Completed the task without aborting")
		End If
		
	End Sub
	

	Private Sub PauseThread()
		t.Sleep(5000)
		ExitFlag = True
	End Sub


End Class

This still does not explain why the timer idea did not work though. Will hold off on calling this thread resolved until we can figure out why that is.