'under Public Class Form1
Private Shared KeepRunning As Boolean

'Settings
Private Shared Threads As Integer = 9
Private Shared ClosedThreads As Integer = 0

'under Start button
KeepRunning = True

For i As Integer = 0 to Threads
	Dim t As New Thread(AddressOf StartThread) With {.IsBackground = True}
	t.Start
Next

'add this sub
Private Sub StartThread
	Dim loops As Integer 

	While KeepRunning
		loops += 1
		Debug.Print($"Running some function in thread ID: {Thread.CurrentThread.ManagedThreadId}, loops: {loops}")
		Thread.Sleep(10000)'Pause this thread for 10 secs.
	End While

	Debug.Print($"Leaving thread (ID={Thread.CurrentThread.ManagedThreadId}), loops: {loops}")

	If Interlocked.Increment(ClosedThreads) > Threads
		ClosedThreads = 0
		Debug.Print("All threads have exited.")
	End If
End Sub

'under Stop button
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
	KeepRunning = False
End Sub