C#

using System;
using System.Threading;
// using...

class Example
{
  bool stop = false;
  AutoResetEvent waitHandle;
  static void Main()
  {
    waitHandle = new AutoResetEvent(false);
    Timer t = new Timer(new TimerCallback(EnumerateWindows), null, 5000,
      Timeout.Infinite);
    waitHandle.WaitOne(); // Wait indefinitely until signalled.
  }
  static void EnumerateWindows(object state)
  {
    if (stop) waitHandle.Set(); // Signal the wait handle.
    else
    {
      // Enumerate your windows as I showed you before here.
    }
  }
  // Declare window enumeration methods and callbacks as I showed you
  // before here.
}

using System;
using System.Runtime.InteropServices;
using System.Threading;

class Test
{
  static AutoResetEvent evt;
  static int count = 1;
  static void Main(string[] args)
  {
    if (args.Length > 0)
    {
      try
      {
        count = int.Parse(args[0]);
      }
      catch {}
    }
    
    evt = new AutoResetEvent(false);
    Timer t = new Timer(new TimerCallback(TimerCallback), null, 0, 5000);
    evt.WaitOne();
  }

  static void TimerCallback(object state)
  {
    Console.WriteLine("Enumerating windows at {0:t}...", DateTime.Now);
    EnumWindows(new EnumWindowsProc(EnumWindowsCallback), IntPtr.Zero);

    if (--count == 0) evt.Set();
  }

  static bool EnumWindowsCallback(IntPtr hWnd, IntPtr lParam)
  {
    if (hWnd != IntPtr.Zero)
    {
      string title = new string('\0', 260);
      int ret = GetWindowText(hWnd, title, 260);
      if (ret != 0)
        Console.WriteLine("0x{0:x8}: {1}", hWnd.ToInt64(),
          title.Substring(0, ret));
    }

    return true;
  }

  [DllImport("user32.dll")]
  static extern bool EnumWindows(EnumWindowsProc proc, IntPtr lParam);

  delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

  [DllImport("user32.dll", CharSet=CharSet.Auto)]
  static extern int GetWindowText(IntPtr hWnd, [Out] string title,
    int maxCount);
}