code: private void addClientToPoolGently(HClient client) {
      try {
        availableClientQueue.add(client);
      } catch (IllegalStateException ise) {
        log.warn("Capacity hit adding client back to queue. Closing extra");
        client.close();
      }
    }
docs: Avoids a race condition on adding clients back to the pool if pool is almost full.
  Almost always a result of batch operation startup and shutdown (when multiple threads
  are releasing at the same time).
  @param client