public void addVersionCheckClientListener(
      boolean triggerStartListener, VersionCheckClientListener l) {
    synchronized (listeners) {
      listeners.add(l);

      if (triggerStartListener && startCheckRan) {
        try {
          l.versionCheckStarted(REASON_UPDATE_CHECK_START);
        } catch (Exception e) {
          Debug.out(e);
        }
      }
    }
  }
  protected Map getVersionCheckInfoSupport(
      String reason, boolean only_if_cached, boolean force, boolean v6) {
    try {
      synchronized (listeners) {
        if (REASON_UPDATE_CHECK_START.equals(reason)) {
          startCheckRan = true;
        }
        for (VersionCheckClientListener l : listeners) {
          l.versionCheckStarted(reason);
        }
      }
    } catch (Throwable t) {
      Debug.out(t);
    }
    if (v6) {

      if (enable_v6) {

        try {
          check_mon.enter();

          long time_diff = SystemTime.getCurrentTime() - last_check_time_v6;

          force = force || time_diff > CACHE_PERIOD || time_diff < 0;

          if (last_check_data_v6 == null || last_check_data_v6.size() == 0 || force) {
            // if we've never checked before then we go ahead even if the "only_if_cached"
            // flag is set as its had not chance of being cached yet!
            if (only_if_cached && last_check_data_v6 != null) {
              return (new HashMap());
            }
            try {
              last_check_data_v6 =
                  performVersionCheck(constructVersionCheckMessage(reason), true, true, true);

              if (last_check_data_v6 != null && last_check_data_v6.size() > 0) {

                COConfigurationManager.setParameter("versioncheck.cache.v6", last_check_data_v6);
              }
            } catch (SocketException t) {
              // internet is broken
              // Debug.out(t.getClass().getName() + ": " + t.getMessage());
            } catch (UnknownHostException t) {
              // dns is broken
              // Debug.out(t.getClass().getName() + ": " + t.getMessage());
            } catch (Throwable t) {
              Debug.out(t);
              last_check_data_v6 = new HashMap();
            }
          } else {
            Logger.log(
                new LogEvent(
                    LOGID,
                    "VersionCheckClient is using "
                        + "cached version check info. Using "
                        + last_check_data_v6.size()
                        + " reply keys."));
          }
        } finally {
          check_mon.exit();
        }
      }

      if (last_check_data_v6 == null) last_check_data_v6 = new HashMap();

      return last_check_data_v6;

    } else {

      try {
        check_mon.enter();

        long time_diff = SystemTime.getCurrentTime() - last_check_time_v4;

        force = force || time_diff > CACHE_PERIOD || time_diff < 0;

        if (last_check_data_v4 == null || last_check_data_v4.size() == 0 || force) {
          // if we've never checked before then we go ahead even if the "only_if_cached"
          // flag is set as its had not chance of being cached yet!
          if (only_if_cached && last_check_data_v4 != null) {
            return (new HashMap());
          }
          try {
            last_check_data_v4 =
                performVersionCheck(constructVersionCheckMessage(reason), true, true, false);

            if (last_check_data_v4 != null && last_check_data_v4.size() > 0) {

              COConfigurationManager.setParameter("versioncheck.cache.v4", last_check_data_v4);
            }

            // clear down any plugin-specific data that has successfully been sent to the version
            // server

            try {
              if (AzureusCoreFactory.isCoreAvailable()) {

                // installed plugin IDs
                PluginInterface[] plugins =
                    AzureusCoreFactory.getSingleton().getPluginManager().getPluginInterfaces();

                for (int i = 0; i < plugins.length; i++) {

                  PluginInterface plugin = plugins[i];

                  Map data =
                      plugin
                          .getPluginconfig()
                          .getPluginMapParameter("plugin.versionserver.data", null);

                  if (data != null) {

                    plugin
                        .getPluginconfig()
                        .setPluginMapParameter("plugin.versionserver.data", new HashMap());
                  }
                }
              }
            } catch (Throwable e) {
            }
          } catch (UnknownHostException t) {
            // no internet
            Debug.outNoStack(
                "VersionCheckClient - " + t.getClass().getName() + ": " + t.getMessage());
          } catch (IOException t) {
            // General connection problem.
            Debug.outNoStack(
                "VersionCheckClient - " + t.getClass().getName() + ": " + t.getMessage());
          } catch (Throwable t) {
            Debug.out(t);
            last_check_data_v4 = new HashMap();
          }
        } else {
          if (Logger.isEnabled())
            Logger.log(
                new LogEvent(
                    LOGID,
                    "VersionCheckClient is using "
                        + "cached version check info. Using "
                        + last_check_data_v4.size()
                        + " reply keys."));
        }
      } finally {
        check_mon.exit();
      }

      if (last_check_data_v4 == null) last_check_data_v4 = new HashMap();

      last_feature_flag_cache_time = 0;

      return last_check_data_v4;
    }
  }