Using tokio_threadpool::blocking for getaddrinfo

[srijs]

I'm wondering how viable it would be to use tokio's blocking feature for dns lookups, removing the need to spawn a thread pool internally.

This could take the shape of something like HttpConnector::default which could be used by default in Client::new.

I know that blocking is used successfully in tokio-fs, but given that a DNS lookup tends to have a much higher worse-case latency, I'm unsure if this is a good idea.

Do you have any thoughts on it?

[sfackler]

blocking will only work if you're running with the threadpool executor, (and not e.g. the current thread executor), so you'd need to be able to configure this. #1517 is related.

[seanmonstar]

I have thought about it briefly, and as you mentioned, I worried about the generally much longer blocking of a DNS lookup vs reading a file that may be in cache.

However, as mentioned, this would prevent the connector from working with any other executor.

[seanmonstar]

I'm going to close for now, since making HttpConnector require tokio-threadpool is not really possible. It should be possible to explore a separate connector that does what this issue describes, though!