presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/SemiTransactionalHiveMetastore.java/SemiTransactionalHiveMetastore/createRole
class SemiTransactionalHiveMetastore:    public synchronized void createRole(String role, String grantor)
    {
        setExclusive((delegate, hdfsEnvironment) -> delegate.createRole(role, grantor));
    }