presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/SemiTransactionalHiveMetastore.java/SemiTransactionalHiveMetastore/listRoles
class SemiTransactionalHiveMetastore:    public synchronized Set<String> listRoles()
    {
        checkReadable();
        return delegate.listRoles();
    }