code: @Override
      protected synchronized JournalInputFile openNextFile()
              throws JournalException {
          while (open) {
              boolean locked = processLockingMechanism();
  
              if (pauseBeforePolling) {
                  try {
                      wait(pollingIntervalMillis);
                  } catch (InterruptedException e) {
                      // no special action on interrupt.
                  }
              }
  
              if (!locked) {
                  JournalInputFile nextFile = super.openNextFile();
                  if (nextFile != null) {
                      return nextFile;
                  }
              }
  
              try {
                  wait(pollingIntervalMillis);
              } catch (InterruptedException e) {
                  // no special action on interrupt.
              }
          }
          return null;
      }
docs: Process the locking mechanism. If we are not locked, we should look for
  another journal file to process. Ask for a new file, using the superclass
  method, but if none is found, wait for a while and repeat. This will
  continue until we get a server shutdown signal.