pgplsql SELECT INTO ... FOR UPDATE (transaction/locking question)

I'm trying to write a stored procedure in plpgsql that selects a row
and possibly increments one of its fields. I thought I would do SELECT
INTO my_record * FROM my_table FOR UPDATE WHERE ..., but apparently
plpgsql doesn't like the FOR UPDATE in a stored procedure. Does
plpgsql automatically lock any rows I read until the stored procedure
exits? I'm just not sure how to get the functionality I'm looking for
and not have to concern myself with concurrency.


Example:

<fixed><fontfamily><param>Courier New</param>create table t_test (x
int, y int);

create or replace function f_test(int) returns void as '

declare r record;

begin

  select into r *, oid from t_test -- FOR UPDATE

    where x = $1;

  if found then

    update t_test set y=y+1 where oid = r.oid;

  end if;

  return;

end' language plpgsql;

insert into t_test values (1,1);

select f_test(1);

</fontfamily></fixed>
I'm trying to write a stored procedure in plpgsql that selects a row
and possibly increments one of its fields. I thought I would do SELECT
INTO my_record * FROM my_table FOR UPDATE WHERE ..., but apparently
plpgsql doesn't like the FOR UPDATE in a stored procedure. Does plpgsql
automatically lock any rows I read until the stored procedure exits?
I'm just not sure how to get the functionality I'm looking for and not
have to concern myself with concurrency.

Example:
create table t_test (x int, y int);
create or replace function f_test(int) returns void as '
declare r record;
begin
   select into r *, oid from t_test -- FOR UPDATE
     where x = $1;
   if found then
     update t_test set y=y+1 where oid = r.oid;
   end if;
   return;
end' language plpgsql;
insert into t_test values (1,1);
select f_test(1);