/** starts the server listens to incoming packets */
 public void run() {
   try {
     while (true) {
       if (Log.loggingNet) Log.net("In RDPServer.run: starting new iteration");
       try {
         Set<DatagramChannel> activeChannels = getActiveChannels();
         activeChannelCalls++;
         Iterator<DatagramChannel> iter = activeChannels.iterator();
         while (iter.hasNext()) {
           DatagramChannel dc = iter.next();
           if (Log.loggingNet) Log.net("In RDPServer.run: about to call processActiveChannel");
           processActiveChannel(dc);
           if (Log.loggingNet) Log.net("In RDPServer.run: returned from processActiveChannel");
         }
       } catch (ClosedChannelException ex) {
         // ignore
       } catch (Exception e) {
         Log.exception("RDPServer.run caught exception", e);
       }
     }
   } finally {
     Log.warn("RDPServer.run: thread exiting");
   }
 }
  /** returns a list of rdpserversockets */
  Set<DatagramChannel> getActiveChannels() throws InterruptedException, java.io.IOException {
    lock.lock();
    try {
      while (channelMap.isEmpty()) {
        channelMapNotEmpty.await();
      }
    } finally {
      lock.unlock();
    }

    Set<SelectionKey> readyKeys = null;
    do {
      lock.lock();
      try {
        if (!newChannelSet.isEmpty()) {
          if (Log.loggingNet) Log.net("RDPServer.getActiveChannels: newChannelSet is not null");
          Iterator<DatagramChannel> iter = newChannelSet.iterator();
          while (iter.hasNext()) {
            DatagramChannel newDC = iter.next();
            iter.remove();
            newDC.register(selector, SelectionKey.OP_READ);
          }
        }
      } finally {
        lock.unlock();
      }
      int numReady = selector.select(); // this is a blocking call - thread safe
      selectCalls++;
      if (numReady == 0) {
        if (Log.loggingNet) Log.net("RDPServer.getActiveChannels: selector returned 0");
        continue;
      }
      readyKeys = selector.selectedKeys();
      if (Log.loggingNet)
        Log.net(
            "RDPServer.getActiveChannels: called select - # of ready keys = "
                + readyKeys.size()
                + " == "
                + numReady);
    } while (readyKeys == null || readyKeys.isEmpty());

    lock.lock();
    try {
      // get a datagramchannel that is ready
      Set<DatagramChannel> activeChannels = new HashSet<DatagramChannel>();

      Iterator<SelectionKey> iter = readyKeys.iterator();
      while (iter.hasNext()) {
        SelectionKey key = iter.next();
        if (Log.loggingNet)
          Log.net(
              "RDPServer.getActiveChannels: matched selectionkey: "
                  + key
                  + ", isAcceptable="
                  + key.isAcceptable()
                  + ", isReadable="
                  + key.isReadable()
                  + ", isValid="
                  + key.isValid()
                  + ", isWritable="
                  + key.isWritable());
        iter.remove(); // remove from the selected key list

        if (!key.isReadable() || !key.isValid()) {
          Log.error(
              "RDPServer.getActiveChannels: Throwing exception: RDPServer: not readable or invalid");
          throw new MVRuntimeException("RDPServer: not readable or invalid");
        }

        DatagramChannel dc = (DatagramChannel) key.channel();
        activeChannels.add(dc);
      }
      if (Log.loggingNet)
        Log.net(
            "RDPServer.getActiveChannels: returning " + activeChannels.size() + " active channels");
      return activeChannels;
    } finally {
      lock.unlock();
    }
  }