docs: public synchronized SessionInfo addLock(Object bookmark, SessionInfo sessionInfo)
      {
          Utility.getLogger().info("Lock: " + bookmark + ", Session: " + sessionInfo.m_iSessionID + " success: " + !this.containsKey(bookmark));
          if (this.containsKey(bookmark))
              return (SessionInfo)this.get(bookmark);   // Error, already locked
          return (SessionInfo)this.put(bookmark, sessionInfo);    // Returns null
      }