ClientService.Interface getRegionServerStub(ServerName serverName) throws IOException {
    return ConcurrentMapUtils.computeIfAbsentEx(rsStubs,
      getStubKey(ClientService.getDescriptor().getName(), serverName),
      () -> createRegionServerStub(serverName));
  }
If choreService has not been created yet, create the ChoreService.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncConnectionImpl.java