Add ready attribute, when exchange is ready

[jpmckinney]

Relevant code: https://github.com/pika/pika/blob/55557c9172edb04256a5e49b7faf13078d5a0f66/examples/blocking_consume_recover_multiple_hosts.py#L54-L63

[jpmckinney]

Witnessed exception classes

• AMQPConnectorSocketConnectError: ConnectionRefusedError
• AMQPConnectionError
• StreamLostError: ConnectionResetError
• ConnectionResetError

ConnectionWrongStateError also witnessed with "BlockingConnection.close(200, 'Normal shutdown') called on closed connection." – I assume this is yapw attempting a clean shutdown after one of the above unhandled exceptions.

[jpmckinney]

This has been implemented in clients. Different clients might want to recover from different errors (and instantiate different clients), so it might be over-complicated to make this reusable in this library, as we'd need to pass the new function a "client factory".

open-contracting/data-registry@517bcf5#diff-5a647a7f71f26fcf662e3f8eab7eb913b41cea4219fb187871d12516fb2ad45b

[jpmckinney]

Noting that we might need to set a "ready" state like we do in Kingfisher Collect and then only run functions when ready.

We can do this as a new function that calls exchange_ready after setting the ready state.

https://github.com/open-contracting/kingfisher-collect/blob/1db352034eb91e004aa50fe48fa8a14885f37dd0/kingfisher_scrapy/extensions/kingfisher_process_api2.py#L15-L25

It might be as simple as changing add_callback_threadsafe to check the ready state:

https://github.com/open-contracting/kingfisher-collect/blob/1db352034eb91e004aa50fe48fa8a14885f37dd0/kingfisher_scrapy/extensions/kingfisher_process_api2.py#L175-L180

[jpmckinney]

Re-opening to upstream the Kingfisher Collect logic, essentially:

class Client(Async):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.ready = False

    def exchange_ready(self):
        self.ready = True

    def reset(self):
        super().reset()
        self.ready = False

Then document the ready attribute with an example of why/when to use it.