Type error in Atomics.waitAsync in Chrome v87+

[KiKoS0]

Describe the Bug

I have a multithreaded wasm app that uses futures-channel-preview for asynchronous communication that suddenly stopped working with Chrome version 87+. I googled a bit to find out that chrome released the Atomics.waitAsync feature and that even the example i used as a reference triggers exactly the same bug.

The problem turned out to be in this function:

wasm-bindgen/crates/futures/src/task/multithread.rs

Lines 158 to 170 in 316c5a7

	fn wait_async(ptr: &AtomicI32, current_value: i32) -> js_sys::Promise {
	// If `Atomics.waitAsync` isn't defined (as it isn't defined anywhere today)
	// then we use our fallback, otherwise we use the native function.
	return if Atomics::get_wait_async().is_undefined() {
	crate::task::wait_async_polyfill::wait_async(ptr, current_value)
	} else {
	let mem = wasm_bindgen::memory().unchecked_into::<js_sys::WebAssembly::Memory>();
	Atomics::wait_async(
	&mem.buffer(),
	ptr as *const AtomicI32 as i32 / 4,
	current_value,
	)
	};

Since Atomics.waitAsync is now defined in Chrome, it is getting used instead of the fallback method, however the function waitAsync is expecting either a Int32Array or a BigInt64Array backed by a SharedArrayBuffer. Also it's not returning a promise anymore but an Object with 2 properties async and value. The value property can either be a string or a promise. (Source)

I fixed the bug for my app in this fork but i'm not really sure if the code is compliant for a PR, not sure if that breaks anything else and also if the other output cases should be handled aswell. I'd be happy to change it accordingly with your input though.

Steps to Reproduce

Just clone and run this example in Chrome 87+ or use the already compiled online one

Expected Behavior

A promise should be returned from wait_async() to be resolved successfully later with a call to Atomics.notify.

Actual Behavior

This error is thrown:
TypeError: #<SharedArrayBuffer> is not an int32 or BigInt64 typed array.

Additional Context

rustc 1.49.0-nightly
futures-channel-preview = "0.3.0-alpha.18"
wasm-bindgen = "0.2.68"

[alexcrichton]

Thanks for the report! Looks like the spec has changed since it was first written (as is to be expected) and I hadn't had a chance to see this and get around to changing the expected API!