wasip3 hostProvided async tasks: top-level resolves too early #1272
Description
Hi all,
I understand that asynchronous support in wasip3 is still in an early stage.
I’m testing wasip3 asynchronous host-provided functions in a JS-WASM setup. Here’s the context:
- WIT definitions
interface opfs-file {
read: async func(path: string) -> string;
write: async func(path: string, data: string) -> u32;
}
world tester-world {
import opfs-file;
export run: async func(path: string);
}- WASM implements only run()
- read / write are provided by a JS shim
- WASM is transpiled via jco, generating JS bindings
- WASM run() implementation
async fn run(path: String) -> () {
println!("Start writing to opfs (path: {})", &path);
let n = opfs_file::write(path.clone(), "foo-bar-baz".into()).await;
println!("End writing to opfs (ret: {})", n);
println!("Start reading from opfs");
println!("contents: `{}`", opfs_file::read(path).await);
}- JS Shim (boilerplate for testing)
export const read = async (path: string): Promise<string> => {
console.info("`read` on shim called");
return "qwerty"; // placeholder for actual async logic
};
export const write = async (path: string, data: string): Promise<number> => {
console.info("`write` on shim called");
return 42; // placeholder for actual async logic
};Note: These are just boilerplate implementations for verification. Real async logic will replace the placeholders.
- Top-level call
await wasm.run("xyz.txt");
console.info("Terminated !");Expected behavior
(wasm)run -> (wasm)write -> (shim)write -> (wasm)read -> (shim)read -> Terminated !
Actual behavior
Start writing to opfs (path: xyz.txt)
Terminated !
`write` on shim called
- read never waits
- Top-level run resolves before subtasks complete
Observations / Analysis
- Subtasks (write / read) are registered as
AsyncTask - _driverLoop() polls subtasks, but top-level task resolves immediately
- Host-provided tasks do not propagate resolution to the top-level task
Question
Is this expected behavior for host-provided tasks? Should the top-level task automatically wait for JS shim completion, or is there a recommended pattern to properly await subtasks in wasip3?
Any guidance or examples would be greatly appreciated.
Thanks!
Environment
- runtime: NodeJS 25.2.1
- jco: 0.17.0
- rust: 1.93.0