work-around for race conditions stemming from SEP threading model

  /*
   * TODO: Looks like SEP calls the *same* MorphlineResultToSolrMapper instance from multiple
   * threads at the same time. This would cause race conditions. It would be more efficient,
   * scalable and simple for SEP to instantiate a separate ResultToSolrMapper instance per thread on
   * program startup (and have one or two threads per CPU core), and have each thread reuse it's own
   * local ResultToSolrMapper many times. For now we use a crude lower-level pooling work-around
   * below.
   */
  private final BlockingQueue<LocalMorphlineResultToSolrMapper> pool = new LinkedBlockingQueue();