condvar wait not supported on wasm32-wasi target

[xtuc]

Hello,

I'm using the current thread runtime and targeting the wasm32-wasi target.
Since tokio-1.21.0 I was expecting it to work, but I'm running into condvar wait not supported. Please see the minimal repro to demonstrate: xtuc/tokio-wasm-repro.

Is that expected? Shouldn't Tokio take advantage of Wasi's poll_oneoff? Also please let me know if this should be an issue.

[Darksonn]

From the documentation:

Note also that if the runtime becomes indefinitely idle, it will panic immediately instead of blocking forever. On platforms that don’t support time, this means that the runtime can never be idle in any way.

This is the situation that you've encountered. Though, the panic message could probably be improved.

[xtuc]

Wasi does support time, is that not implemented in Tokio's wasm support yet?

[Darksonn]

Time is supported on wasi, but you have no timers, so it is irrelevant. Let me quote the important part specifically:

Note also that if the runtime becomes indefinitely idle, it will panic immediately instead of blocking forever.

[xtuc]

Time is supported on wasi, but you have no timers

@Darksonn please forgive my ignorance but isn't that what poll_oneoff is enabling?

poll_oneoff subscriptions include:

clock The time value of clock subscription_clock::id has reached timestamp subscription_clock::timeout.

[Darksonn]

You misunderstand. I meant "there are no timers in your program", not "wasi does not support timers".