declare
  counter number;
  cursor c is
    select * from my_table
    where ... -- условия для выбора блокируемой строки
    for update nowait;
  rec c%rowtype;
begin
  counter :=  0 ;
  loop
    begin
      counter := counter +  1 ;
      open c;
      fetch c into rec;
      if c%notfound then
       close c;
       fnd_message.set_name('FND','FORM_RECORD_DELETED');
       fnd_message.error;
       raise form_trigger_failure;
      end if;
      close c;
      if (rec.field1 = :block_name.field1 or
          rec.field1 is null and :block_name.field1 is null) and
        -- и т.д. по всем полям
      then
        exit;
      else
        fnd_message.set_name('FND','FORM_RECORD_CHANGED');
        fnd_message.error;
        raise form_trigger_failure;
      end if;
    exception
      when app_exceptions.record_lock_exception then
         if c%isopen then
           close c;
         end if;
         app_exception.record_lock_error(counter);
    end;
  end loop;
end;

fnd_message.set_name(...);
fnd_message.error;
raise form_trigger_failure;

и

app_exception.record_lock_error(counter);