private void preCheck() {
      checkArgument(scannerId != null, "invalid scannerId %d", scannerId);
      checkNotNull(scan, "scan is null");
      checkNotNull(resultCache, "resultCache is null");
      checkNotNull(consumer, "consumer is null");
      checkNotNull(stub, "stub is null");
      checkNotNull(loc, "location is null");
      this.priority = calcPriority(priority, loc.getRegion().getTable());
    }
Create retry caller for single action, such as get, put, delete, etc.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncRpcRetryingCallerFactory.java