Grow Your Own Concurrency Problem ....oracle

What's that? the sound of ORA-00001: approaching...

...
FUNCTION key_not_in_table(pkey IN INT) RETURN BOOLEAN
IS
 countkey INT;
BEGIN
 SELECT count(key) INTO countkey
 FROM key_values WHERE key = pkey;

 IF countkey > 0 THEN
  RETURN FALSE;
 END IF;
 RETURN TRUE;

END key_not_in_table;

PROCEDURE insert_or_update(pkey IN INT,
  pval IN INT)
IS
BEGIN
 IF key_not_in_table(pkey) THEN
  INSERT INTO key_values
  VALUES (key, value, 0);
 ELSE
  UPDATE key_values
  SET value =  pval
  WHERE key = pkey;
 END IF;
END insert_or_update;