Lock conflict behavior?

Hi,

I'm wondering if following behavior of PostgreSQL regarding lock
conflict is an expected one. Here's a scenario:

Session A:
BEGIN;
SELECT * FROM pg_class limit 1; -- acquires access share lock

Session B:
BEGIN;
ALTER TABLE pg_class ....; -- waits for acquiring access
exclusive lock(wil fail anyway though)
Session C:
SELECT * FROM pg_class...; -- whatever query which needs
to acces pg_class will be
blocked, too bad...

I understand that B should wait for aquiring lock, but Should C wait
for?

Also, it seems that an attacker could do a denial service attack if he
could open session A and B, since other users on session C or
following sessions will be blocked.
--
Tatsuo Ishii
SRA OSS, Inc. Japan