private void doSplitting() {
    server.getMetrics().incrSplitRequest();
    if (user != null && user.getUGI() != null) {
      user.getUGI().doAs((PrivilegedAction<Void>) () -> {
        requestRegionSplit();
        return null;
      });
    } else {
      requestRegionSplit();
    }
  }
Handles processing region splits. Put in a queue, owned by HRegionServer.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/SplitRequest.java