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Imports System.Threading

Public Class SyncEvents
	Private _newItemEvent As EventWaitHandle
	Public ReadOnly Property NewItemEvent() As EventWaitHandle
		Get
			Return _newItemEvent
		End Get
	End Property

	Private _exitThreadEvent As EventWaitHandle
	Public ReadOnly Property ExitThreadEvent() As EventWaitHandle
		Get
			Return _exitThreadEvent
		End Get
	End Property

	Private _eventArray As WaitHandle()
	Public ReadOnly Property EventArray() As WaitHandle()
		Get
			Return _eventArray
		End Get
	End Property

	Public Sub New()
		_newItemEvent = New AutoResetEvent(False)
		_exitThreadEvent = New ManualResetEvent(False)
		_eventArray = New WaitHandle() {_newItemEvent, _exitThreadEvent}
	End Sub
End Class

Public Class Producer
	Private _queue As Queue(Of Integer)
	Private _syncEvents As SyncEvents

	Public Sub New(ByVal q As Queue(Of Integer), ByVal e As SyncEvents)
		_queue = q
		_syncEvents = e
	End Sub

	Public Sub ThreadRun()
		Dim count As Integer = 0
		Dim r As New Random()
		While Not _syncEvents.ExitThreadEvent.WaitOne(0, False)
			SyncLock DirectCast(_queue, ICollection).SyncRoot
				While _queue.Count < 20
					_queue.Enqueue(r.Next(0, 100))
					_syncEvents.NewItemEvent.Set()
					count += 1
				End While
			End SyncLock
		End While
		Console.WriteLine("Producer thread: produced {0} items", count)
	End Sub
End Class

Public Class Consumer
	Private _queue As Queue(Of Integer)
	Private _syncEvents As SyncEvents

	Public Sub New(ByVal q As Queue(Of Integer), ByVal e As SyncEvents)
		_queue = q
		_syncEvents = e
	End Sub

	Public Sub ThreadRun()
		Dim count As Integer = 0
		While WaitHandle.WaitAny(_syncEvents.EventArray) <> 1
			SyncLock DirectCast(_queue, ICollection).SyncRoot
				Dim item As Integer = _queue.Dequeue()
				count += 1
			End SyncLock
		End While
		Console.WriteLine("Consumer thread: consumed {0} items", count)
	End Sub
End Class

Public Class Program
	Private Shared Sub ShowQueueContents(ByVal q As Queue(Of Integer))
		SyncLock DirectCast(q, ICollection).SyncRoot
			For Each item As Integer In q
				Console.Write("{0} ", item)
			Next
		End SyncLock
		Console.WriteLine()
	End Sub

	Public Shared Sub Main()
		Dim queue As New Queue(Of Integer)
		Dim syncEvent As New SyncEvents()

		Console.WriteLine("Configuring worker threads...")

		Dim producer As New Producer(queue, syncEvent)
		Dim cunsumer As New Consumer(queue, syncEvent)

		Dim producerThread As New Thread(AddressOf producer.ThreadRun)
		Dim consumerThread As New Thread(AddressOf cunsumer.ThreadRun)

		Console.WriteLine("Launching producer and consumer threads...")

		producerThread.Start()
		consumerThread.Start()

		For i As Integer = 0 To 3
			Thread.Sleep(2500)
			ShowQueueContents(queue)
		Next i

		Console.WriteLine("Signaling threadds to terminate...")

		syncEvent.ExitThreadEvent.Set()

		producerThread.Join()
		consumerThread.Join()
	End Sub
End Class