code: public synchronized static void clearObsoleteImageUploads(long minTxIdToKeep,
        String journalId) {
      for (Iterator<Map.Entry<Long, SessionDescriptor>> it = sessions.entrySet()
          .iterator(); it.hasNext();) {
        Map.Entry<Long, SessionDescriptor> entry = it.next();
        if (entry.getValue().journalId.equals(journalId)
            && entry.getValue().txid < minTxIdToKeep) {
          it.remove();
        }
      }
    }
docs: Clean the map from obsolete images.