Ack/nack hangs when channel is closed after cancellation

[ThomWright]

When a channel gets cancelled with basic_cancel() while messages are being processed, then:

• When in the Closing state, calling nack() on a delivery returns an error as expected: invalid channel state: Closing.
• After the channel gets closed and removed, the call to nack() never resolves.

I suspect this is somewhat similar to #409, maybe?

I can try to put together a reproducing example if that's helpful.

[Keruspe]

This is very interesting thanks.
A reproducer would be appreciated to speed up the debugging

[ThomWright]

Will do!

I've been unable to reproduce with a smaller example, so I'll need to dig deeper.

[ThomWright]

I can only reproduce inside a #[tokio::test]. Inside #[tokio::main] it seems to work just fine! 😕

At this point I'm suspecting that this is some tokio/executor/runtime-related "I'm holding it wrong" issue, and probably not a lapin issue! So feel free to ignore/close if you suspect the same.

I've made a repro here with both a main function and a test function if you're interested.

[matt961]

I can only reproduce inside a #[tokio::test]. Inside #[tokio::main] it seems to work just fine! 😕

Perhaps it is related to a deadlock of tasks on single thread runtime. https://docs.rs/tokio/latest/tokio/attr.test.html#current-thread-runtime