Lock on arbitrary string feature

Hi,

Has anyone any input to offer on adding an arbitrary locking feature?

Where
GETLOCK "string" will lock on "string", the lock being only released at the
end of a transaction.

While the lock is held, other processes trying to do GETLOCK "string" will
block until the lock is released.

This feature can allow applications to better serialize things. For
example: inserting unique records. Cooperating applications could just do
something like:

GETLOCK "mytable.key2=1234";
SELECT count(*) from mytable where key2=1234 for update;
if count==0, insert the stuff.
 elsif count==1 update the stuff instead
 else something is wrong!

The lock will thus only affect applications interested in mytable where
key2=1234

In contrast the current alternatives appear to be either LOCK the entire
table (preventing ALL inserts and selects), or to create a UNIQUE
constraint (forcing complete rollbacks and restarts in event of a collision
:( ).

Any comments, suggestions or tips would be welcome. It looks like quite a
complex thing to do - I've only just started looking at the postgresql
internals and the lock manager.

Cheerio,
Link.