Futures should be woken before calling Future::poll

[yoshuawuyts]

Problem

Following up on #71, we still have some issues. In #70 (comment) @SilverMira provided the following failing test case:

 #[test]
 fn cooperative_concurrency() {
 crate::runtime::block_on(async {
 let cpu_heavy = async move {
 // Simulating a CPU-heavy task that runs for 10 second and yields occasionally
 for _ in 0..100 {
 std::thread::sleep(std::time::Duration::from_millis(100));
 futures_lite::future::yield_now().await;
 }
 true
 };
 let timeout = async move {
 crate::time::Timer::after(crate::time::Duration::from_secs(3))
 .wait()
 .await;
 false
 };
 let mut future_group = futures_concurrency::future::FutureGroup::<
 Pin<Box<dyn std::future::Future<Output = bool>>>,
 >::new();
 future_group.insert(Box::pin(cpu_heavy));
 future_group.insert(Box::pin(timeout));
 let result = future_group.next().await;
 assert_eq!(result, Some(false), "cpu_heavy task should have timed out");
 });
 }

From talking with @pchickey, it sounds like we are currently not calling the wakers before re-polling, which is causing the test to fail. We should write a patch to fix that.

Proposed Solution

The solution @pchickey is proposing is to add a non-blocking version of Reactor::block_on_pollables which calls wasi::io::poll::poll on every async pollable with a waker registered. We need a variation in the behavior that adds an additional pollable to the wasi poll list, so that wasi::io::poll::poll does not block and immediately returns a ready list, and wakes all of the associated wakers. We should insert that call right below the following line:

https://github.com/yoshuawuyts/wstd/blob/90bb588c4f10030e2ac6fcdb13860d7da1a62b8d/src/runtime/block_on.rs#L40

[teohhanhui]

Could this bug cause the AsyncInputStream::ready to never poll ready? In my code I'm observing that this never returns:

wstd/src/io/streams.rs

Line 37 in eab1d6e

self.ready().await;

[SilverMira]

Could this bug cause the AsyncInputStream::ready to never poll ready? In my code I'm observing that this never returns:

You can try patching the dependency with
https://github.com/SilverMira/wstd/tree/allow_independent_futures and see whether that fixes things, although keep in mind this implementation is still the older one that isn't too optimized since poll::poll is used with an immediate rather than Pollable::ready

[teohhanhui]

@SilverMira:

You can try patching the dependency with https://github.com/SilverMira/wstd/tree/allow_independent_futures and see whether that fixes things

It actually does work! Thank you.