RPC call/cast should end quickly if no connection

[Rodolfo Alonso]

In Neutron (and many other projects), "cast" is used to notify other services about some specific events (e.g.: a new port creation), by calling a RPC in this external process.

If the message queue is down, the "cast" method call chain is the following:
-> client._CaseCallContext.cast
-> transport.Transport.send
-> amqpdriver.AMQPDriver.send -> _send -> _get_connection [1]

Because RabbitMQ is down and there is no timeout/max_retries flag, the method never returns and the "cast" call does not finish.

Is it possible to, in case of no connection to the MQ, end quickly the "call"/"cast" call? Returning an exception or any other kind of error, but avoiding to be in an endless loop inside the driver.

Thank you in advance. Please, if you want to talk about this, my nickname is "ralonsoh". I'm in #openstack-neutron and #openstack-oslo, UTC time.

[1] https://opendev.org/openstack/oslo.messaging/src/branch/master/oslo_messaging/_drivers/amqpdriver.py#L608