Server reports "Already running a prediction" during setup

[evilstreak]

It should say it's doing setup and isn't ready, instead!

[mattt]

It looks like this was introduced by #944 with these lines:

https://github.com/replicate/cog/blob/dfff002e275cdb6af8af4cc290e976813a4a8735/python/cog/server/runner.py#L57-L59

@nickstenning Would it make sense to raise a different error here?

Also, it looks like is_busy has side effects here, which I wasn't expecting... Is that right?

https://github.com/replicate/cog/blob/dfff002e275cdb6af8af4cc290e976813a4a8735/python/cog/server/runner.py#L141-L142

[nickstenning]

Yes, that's right. It looks weird, and isn't terribly elegant, but note that you can't reach those lines unless it's actually not busy.

The smallest fix here is probably to return a different message with the 409 based on the value of app.state.health.

[Pankaj-Samyak]

Does anyone know how long it takes to Cog for starting up the first time when running it in a Docker container?