.await inside .spawn() stuck indefinitely

[Systemcluster]

While testing some async code shuffling handles between threads I came across a case where .await inside .spawn() doesn't return.

I created a repro case here: https://github.com/Systemcluster/switchyard/blob/trunk/tests/repro.rs

Running with cargo test -- --nocapture makes it apparent that one of the futures gets stuck here: https://github.com/Systemcluster/switchyard/blob/trunk/tests/repro.rs#L25

---

While simplifying the repro case I narrowed it down a bit: If the inner load function doesn't get passed an Arc containing the Switchyard, it doesn't get stuck.

Changing these two lines

async fn load(_name: String, _yard: Arc<Switchyard<()>>) -> Self {
//...
let resource = ResourceA::load(name.clone(), _yard);

to

async fn load(_name: String) -> Self {
// ...
let resource = ResourceA::load(name.clone());

makes it work as expected without getting stuck.

[cwfitzgerald]

Repeating what we discussed on discord:

https://github.com/Systemcluster/switchyard/blob/trunk/tests/repro.rs#L14 dropping yard here is the last reference to switchyard, which drops switchyard, which waits on all threads to be finished. This causes the switchyard worker thread to wait for itself to finish.

So this seems to be a user bug, but should we detect this situation and not block on drop?