private long elapsedMs() {
    return TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - nextCallStartNs);
  }
This method is used when {@link ScanControllerImpl#suspend} had ever been called to get a
{@link ScanResumerImpl}, but now user stops scan and does not need any more scan results.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncScanSingleRegionRpcRetryingCaller.java