async/await: Sending Waker seems to invalidate it

[JOOpdenhoevel]

Hello everyone!

I recently started playing around with the new async/await features and wanted to implement a simple channel using the crossbeam channel and the new futures. The crossbeam channel itself isn't futures-aware, neither 0.1 futures nor the new ones, and therefore, I added another internal channel that sends wakers to the sender and when a new value is sent, the sender will wake all enqueued tasks.

My code is found in this repo: https://github.com/Janonard/rust-noopwake-bug

I expect the program to print 42 and then finish, which is often the case, but not always: Sometimes, I get an error saying thread 'tokio-runtime-worker-2' panicked at 'NoopWake cannot wake' (backtrace found here) and sometimes a simple thread 'tokio-runtime-worker-2' panicked at 'called 'Result::unwrap()' on an 'Err' value: ()' (backtrace found here). Also, after panicing, the program hangs.

Is this a bug within rust, tokio or crossbeam or have I simply made something wrong?

Meta

rustc --version --verbose:

rustc 1.33.0-nightly (09d6ab90e 2018-12-20)
binary: rustc
commit-hash: 09d6ab90e556bf692ff3f8790d97b3ca4fee94b0
commit-date: 2018-12-20
host: x86_64-unknown-linux-gnu
release: 1.33.0-nightly
LLVM version: 8.0

[cramertj]

This is unrelated to rust-lang/rust-- can you open an issue on the futures repository?

[gralpli]

@Janonard Today I stumbled upon what seems to be the same panic and I created a more minimal example (see here). Did you already open an issue on another repo? (I'm not sure if this belongs to tokio, futures or async/await.)