@Override
  public byte[] execProcedureWithReturn(String signature, String instance,
    Map<String, String> props) throws IOException {
    return get(admin.execProcedureWithReturn(signature, instance, props));
  }
The {@link Admin} implementation which is based on an {@link AsyncAdmin}.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AdminOverAsyncAdmin.java