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