@Override public CheckResult check() {
    if (lazyInit.result == null) {
      return CheckResult.failed(new IllegalStateException("Collector not yet started"));
    }
    return lazyInit.result.checkResult;
  }
Count of concurrent message listeners on the queue. Defaults to 1
zipkin-collector/activemq/src/main/java/zipkin2/collector/activemq/ActiveMQCollector.java