/**
  * a DatagramChannel has data ready - process all the pending packets, whether its for a
  * rdpserversocket or rdpconnection.
  */
 void processActiveChannel(DatagramChannel dc) throws ClosedChannelException {
   RDPPacket packet;
   int count = 0;
   // read in the packet
   try {
     Set<RDPConnection> needsAckConnections = new HashSet<RDPConnection>();
     while ((packet = RDPServer.receivePacket(dc)) != null) {
       if (Log.loggingNet)
         Log.net(
             "RDPServer.processActiveChannel: Starting iteration with count of "
                 + count
                 + " packets");
       // see if there is a connection already for this packet
       InetAddress remoteAddr = packet.getInetAddress();
       int remotePort = packet.getPort();
       int localPort = dc.socket().getLocalPort();
       ConnectionInfo conInfo = new ConnectionInfo(remoteAddr, remotePort, localPort);
       RDPConnection con = RDPServer.getConnection(dc, conInfo);
       if (con != null) {
         if (Log.loggingNet)
           Log.net("RDPServer.processActiveChannel: found an existing connection: " + con);
         count++;
         if (processExistingConnection(con, packet)) needsAckConnections.add(con);
         // Prevent this from blocking getActiveChannels by
         // putting an upper bound on the number of packets
         // processed
         if (count >= 20) break;
         continue;
       } else {
         Log.net("RDPServer.processActiveChannel: did not find an existing connection");
       }
       // there is no connection,
       // see if there is a socket listening for new connection
       RDPServerSocket rdpSocket = RDPServer.getRDPSocket(dc);
       if (rdpSocket != null) {
         count++;
         processNewConnection(rdpSocket, packet);
         return;
       }
       return;
     }
     // Finally, send out the acks
     for (RDPConnection con : needsAckConnections) {
       RDPPacket replyPacket = new RDPPacket(con);
       con.sendPacketImmediate(replyPacket, false);
     }
   } catch (ClosedChannelException ex) {
     Log.error("RDPServer.processActiveChannel: ClosedChannel " + dc.socket());
     throw ex;
   } finally {
     if (Log.loggingNet)
       Log.net("RDPServer.processActiveChannel: Returning after processing " + count + " packets");
   }
 }
  /** 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();
    }
  }