/**
   * removes this connection from the connections map the datagram channel still sticks around in
   * case it needs to be reused
   */
  static void removeConnection(RDPConnection con) {
    lock.lock();
    try {
      if (Log.loggingNet) Log.net("RDPServer.removeConnection: removing con " + con);
      con.setState(RDPConnection.CLOSED);

      DatagramChannel dc = con.getDatagramChannel();

      // first we get the set of connections attached to the given dc
      Map<ConnectionInfo, RDPConnection> dcConMap = allConMap.get(dc);
      if (dcConMap == null) {
        throw new MVRuntimeException("RDPServer.removeConnection: cannot find dc");
      }

      int localPort = con.getLocalPort();
      int remotePort = con.getRemotePort();
      InetAddress remoteAddr = con.getRemoteAddr();
      ConnectionInfo conInfo = new ConnectionInfo(remoteAddr, remotePort, localPort);
      Object rv = dcConMap.remove(conInfo);
      if (rv == null) {
        throw new MVRuntimeException("RDPServer.removeConnection: could not find the connection");
      }

      // close the datagramchannel if needed
      // conditions: no other connections on this datagramchannel
      // no socket listening on this datagramchannel
      if (dcConMap.isEmpty()) {
        Log.net("RDPServer.removeConnection: no other connections for this datagramchannel (port)");
        // there are no more connections on this datagram channel
        // check if there is a serversocket listening
        if (getRDPSocket(dc) == null) {
          Log.net("RDPServer.removeConnection: no socket listening on this port - closing");
          // no socket either, close the datagramchannel
          dc.socket().close();
          channelMap.remove(localPort);
          Log.net("RDPServer.removeConnection: closed and removed datagramchannel/socket");
        } else {
          Log.net("RDPServer.removeConnection: there is a socket listening on this port");
        }
      } else {
        Log.net("RDPServer.removeConnection: there are other connections on this port");
      }
    } finally {
      lock.unlock();
    }
  }
  /**
   * Remove particular entry from the trash directory or subdirectory.
   *
   * @param parentId Parent ID.
   * @param id Entry id.
   * @throws IgniteCheckedException If delete failed for some reason.
   */
  private void deleteDirectory(IgniteUuid parentId, IgniteUuid id) throws IgniteCheckedException {
    assert parentId != null;
    assert id != null;

    while (true) {
      IgfsFileInfo info = meta.info(id);

      if (info != null) {
        assert info.isDirectory();

        Map<String, IgfsListingEntry> listing = info.listing();

        if (listing.isEmpty()) return; // Directory is empty.

        Map<String, IgfsListingEntry> delListing;

        if (listing.size() <= MAX_DELETE_BATCH) delListing = listing;
        else {
          delListing = new HashMap<>(MAX_DELETE_BATCH, 1.0f);

          int i = 0;

          for (Map.Entry<String, IgfsListingEntry> entry : listing.entrySet()) {
            delListing.put(entry.getKey(), entry.getValue());

            if (++i == MAX_DELETE_BATCH) break;
          }
        }

        GridCompoundFuture<Object, ?> fut = new GridCompoundFuture<>();

        // Delegate to child folders.
        for (IgfsListingEntry entry : delListing.values()) {
          if (!cancelled) {
            if (entry.isDirectory()) deleteDirectory(id, entry.fileId());
            else {
              IgfsFileInfo fileInfo = meta.info(entry.fileId());

              if (fileInfo != null) {
                assert fileInfo.isFile();

                fut.add(data.delete(fileInfo));
              }
            }
          } else return;
        }

        fut.markInitialized();

        // Wait for data cache to delete values before clearing meta cache.
        try {
          fut.get();
        } catch (IgniteFutureCancelledCheckedException ignore) {
          // This future can be cancelled only due to IGFS shutdown.
          cancelled = true;

          return;
        }

        // Actual delete of folder content.
        Collection<IgniteUuid> delIds = meta.delete(id, delListing);

        if (delListing == listing && delListing.size() == delIds.size())
          break; // All entries were deleted.
      } else break; // Entry was deleted concurrently.
    }
  }