title: Port scanning using threadpool
body: <p>I am trying to run a small app that scans ports and checks to see if they are open using and practicing with threadpools.  The console window will ask a number and scans ports from 1 to X and will display each port whether they are open or closed.  My problem is that as it goes through each port, it sometimes stops prematurely.  It doesn't stop at just one number either, its pretty random.  For example it I specify 200.  The console will scroll through each port then stops at 110.  Next time I run it, it stops at 80.</p>
  
  <p>Code
  Left out some of the things, assume all variables are declared where they should. First part is in Main.</p>
  
  <pre><code>static void Main(string[] args)
      {
          string portNum;
          int convertedNum;
          Console.WriteLine("Scanning ports 1-X");
          portNum = Console.ReadLine();
          convertedNum = Convert.ToInt32(portNum);
          try
          {
              for (int i = 1; i &lt;= convertedNum; i++)
              {
                  ThreadPool.QueueUserWorkItem(scanPort, i);
                  Thread.Sleep(100);
  
              }
          }
          catch (Exception e)
          {
             Console.WriteLine("exception " + e);
          }
      }
  
      static void scanPort(object o)
      {
          TcpClient scanner = new TcpClient();
          try
          {
              scanner.Connect("127.0.0.1",(int)o);
              Console.WriteLine("Port {0} open", o);
          }
          catch
          {
              Console.WriteLine("Port {0} closed",o);
          }
      }
  
  }
  </code></pre>