create or alter procedure lock_first_free (
    a_updatable_view varchar(31),
    a_start_id dm_ids, -- bigint not null
    a_raise_exc dm_sign default 1 -- smallint default 0 not null check (value in(-1, 1, 0))
)
returns (
    locked_id bigint)
AS
declare s varchar(128);
  declare u varchar(128);
  declare v_key dm_dbkey; -- char(8) character set octets  collate octets
  declare v_cnt int = 0;
begin
  -- tries to LOCK record in A_UPDATABLE_VIEW with first ID >= a_start_id;
  -- returns "normal" number = ID if record has been SUCCESSFULLY locked,
  -- otherwise raise ex_can_not_lock_any_record (if a_raise_exc = 1)
  -- or returns "huge negative" number = -fn_infinity()
  -- Samples:
  -- select * from lock_first_free('t', 10); ==> returns first locked ID or exception
  -- select * from lock_first_free('t', 10, 0); ==> returns first locked ID or -fn_infinity()
  locked_id = -fn_infinity();
  s = 'select rdb$db_key from '||:a_updatable_view||' where id>=:a_id order by id';
  u='update '||:a_updatable_view||' set id = id where rdb$db_key = :a_key returning id';
  for execute statement (s) ( a_id := a_start_id ) into v_key
  do begin
    v_cnt = v_cnt+1;
    execute statement(u) ( a_key := v_key ) into locked_id;
    suspend;
    leave;
    when any do begin end
  end
  if (v_cnt = 0) then
    exception ex_record_not_found;
  else if (locked_id = -fn_infinity()) then
  begin
    if ( a_raise_exc = 1) then
      exception ex_can_not_lock_any_record using( upper(:a_updatable_view), :a_start_id);
     --ex_can_not_lock_any_record 'no records could be locked in table @1 with ID >= @2.';
    else
      suspend;
  end
end