timeouts on transactions etc?

Does Postgres have any mechanisms where one can set an activity timeout, say
either dynamically thru SQL to affect a current session, or alternately in a
configuration file so to take effect globally?

I mean for example so we can tell Postgres to automatically abort/rollback a
current statement or transaction if it is still running after 5 seconds? It
would return an error / throw an exception at the same time, as if there was a
failure or constraint violation for some other reason, so the user would know.

Or a generalization of this would be the DBMS enforcing particular resource
limits, but I suspect that just clock time is a relatively easy one to do, as it
could be implemented with ordinary timers and signals/interrupts.

Purposes of this feature include coping with applications that are not
well-behaved such as by failing to explicitly end transactions or by asking the
DBMS to do too much at once.

If so, where is this documented? If not, how much work might it be to add this?

I'm looking for something enforced by the DBMS itself, not that an application
or bridge layer should do.

-- Darren Duncan