It is intended that portrelease is run by the initscript of the service wanting the port. For example, the cups initscript might run portrelease cups.
An exit code of zero means that a best effort attempt has been made to instruct the daemon to release the port. Non-zero exit codes mean that the daemon is running but couldn't be contacted.
portreserve(1)
Tim Waugh <twaugh@redhat.com>