code: private void unlock(Object holder) throws PSQLException {
      if (lockedFor != holder) {
        throw new PSQLException(GT.tr("Tried to break lock on database connection"),
            PSQLState.OBJECT_NOT_IN_STATE);
      }
      lockedFor = null;
      this.notify();
    }
docs: Release lock on this connection presumably held by given object.
  
  @param holder object that holds the lock. Normally current thread.
  @throws PSQLException when this thread does not hold the lock