Pool and connect() with Momoko 2.0.0

[vejnar]

I am trying to switch to Momoko 2.0.0 but I have a two problems.

• In the tutorial, these lines call the connect() method:

future = application.db.connect()
ioloop.add_future(future, lambda f: ioloop.stop())
ioloop.start()

I am using a Pool. When I init one and directly call execute() on it, I get:

assert self.conns.dead, "BUG: dont' call reanimate when there is no one to reanimate"

Which is fixable by adding the 3 lines above. It wasn't like that with the previous version. Is connecting first necessary now? Could you please clarify? BTW not requiring a first connect would be nice.

• In the tutorial, an ioloop instance created with ioloop = IOLoop.instance() is passed to init a Pool. Is that necessary?

Thanks a lot for your help and for developing and maintaining Momoko. It's great!

[haizaar]

Yes, you need to connect. Previously Pool was connecting implicitly in the constructor. I have changed it for several reasons:

• You'd want to connect to db before starting to serve http requests. So you need to init Pool and wait it to connect to db before you start listening. Previously Pool used a on_connect_callback that you can use to get notified that all connection attempts are finished. Now we use futures, but you can not return a future from a constructor, so a separate method is required. This approach also hints a user that he'll better wait this future to resolve to make sure that database is ready. I guess previously some people were just initializing Pool "blindly" and since connections were created quite fast, never noticed that they have a race condition - which may work, but it's not how we want to build software, right?
• I believe that from OOP perspective, creating db connections is not a part of Pool object initialization. And there is no real need to bind them together. So I did the separation.
• You may want to inspect db connectivity state and do something different if, for example, database service is dead, instead of always firing up HTTP server.

Regarding your second question: Pool constructor will do self.ioloop = ioloop or IOLoop.instance() if you don't pass your own ioloop instance. The tutorial does this explicitly to demonstrate the ability.

[vejnar]

OK. Thanks. Would be nice to clarify that in the tutorial.

[haizaar]

You are welcome to submit a pull request :)