memory leaks when threading

    // begin test code in FormMain class
    // also need "using System.Threading;" 
    private System.Threading.AutoResetEvent testThreadBeginWorkEvent = new AutoResetEvent(false);
    private System.Threading.AutoResetEvent testThreadWorkDoneEvent = new AutoResetEvent(false);
    Thread testThread;
    private void testThreadProc()
    {
      try
      {
        while (true) 
        {
          testThreadBeginWorkEvent.WaitOne();
          // by commenting out the entire using block below, the memory leak is plugged
          using (Aurigma.GraphicsMill.BitmapData bitmapData = bitmapViewerMainView.Bitmap.LockBits())
          {
            IntPtr bitmapPtr = bitmapData.Scan0; // using this causes memory leak
            for (int row = 0; row < bitmapViewerMainView.Bitmap.Height; row++)
            {
              bitmapPtr = (IntPtr)((int)bitmapPtr + bitmapData.Stride);
            }
            bitmapViewerMainView.Bitmap.UnlockBits(bitmapData);
          }
          testThreadWorkDoneEvent.Set();
        }
      }
      catch 
      {
      }
    }
    private void FormMain_Closing(object sender, System.ComponentModel.CancelEventArgs e)
    {
      testThread.Abort();
      testThread.Join();
    }
    // end test code in FormMain class

    // begin test code in menu item handler, e.g. MenuItemGrayscale_Click()
    // create the test thread
    if (testThread == null)
    {
      testThread = new Thread(new ThreadStart(testThreadProc));
      testThread.Start();
    }
    // signal the thread several times
    for (int i=0; i<1000; i++) 
    {
      testThreadBeginWorkEvent.Set();
      testThreadWorkDoneEvent.WaitOne();
    }
    return;
    // end test code in menu item handler