using System;
using System.Collections.Generic;
using System.Threading;
using System.Diagnostics;

//*****************************************************************************
public class SyncQueue <T>
{
   //--------------------------------------------------------------------------
   private Queue <T> _q   = new Queue <T> ();

   //==========================================================================
   // <summary>Trägt einen Eintrag (ohne zu warten) ein</summary>
   public void Enqueue (T tItem)
   {
      lock (this) {
         _q.Enqueue (tItem);
         Monitor.Pulse (this);
         Debug.WriteLine (Thread.CurrentThread.Name + " Enqueue ==> " + _q.Count);
      }
   }

   //==========================================================================
   // <summary>
   //    Holt einen Eintrag aus der Queue heraus und wartet dabei nötigenfalls
   //    solange bis wieder ein Eintrag vorhanden ist.
   // </summary>
   public T Dequeue ()
   {
      lock (this) {
         while (_q.Count == 0) {
            Debug.WriteLine (Thread.CurrentThread.Name + " Wait");
            Monitor.Wait (this);
         }
         Debug.WriteLine (Thread.CurrentThread.Name + " Dequeue ==> " + (_q.Count - 1));
         return _q.Dequeue ();
      }
   }
}

//*****************************************************************************
static class App
{
   //-------------------------------------------------------------------------
   private static SyncQueue <int> _sq   = new SyncQueue <int> ();
   private static Random          _rand = new Random ();

   //==========================================================================
   public static void Main (string [] astrArg)
   {
      Debug.Listeners.Clear ();
      Debug.Listeners.Add (new ConsoleTraceListener ());

      for (int i = 0; i < 4; ++i) {
         Thread t = new Thread (RunDequeue);
         t.Name = "D" + i;
         t.Start ();
      }

      for (int i = 0; i < 4; ++i) {
         Thread t = new Thread (RunEnqueue);
         t.Name = "E" + i;
         t.Start ();
      }

   }

   //==========================================================================
   private static void RunEnqueue ()
   {
      for (int i = 1 ; i ≤ 25; ++i) {
         _sq.Enqueue (100);
         Thread.Sleep (_rand.Next (1000));
      }
   }

   //==========================================================================
   private static void RunDequeue ()
   {
      for (int i = 1 ; i ≤ 25; ++i) {
         _sq.Dequeue ();
         Thread.Sleep (_rand.Next (995));
      }
   }
}