libpq program SELECT FOR UPDATE and TIMEOUT or CANCEL REQUEST

Hi,

I am programming using libpq under Linux.

When I do a "select ... for update" to lock a row, how 
would I allow user to cancel or timeout when requesting the
the same row from another program/transaction.

I do not want the user to have to wait for the update on the 
other end. I would rather send the user an error message
saying that the record is LOCKED -- try again later.

If you could send me an example that would be great!

Thanks for your help.

Jeff.

jpogo@imcg.com