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Component `Func::call` (sync call) can fail due to a lack of event loop

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
30/100
Tipo de issue
Nueva funcionalidad
Claridad
Bastante claro
Estado de actividad
Activo
Stack tecnológico
rust
Área
backend

Línea de trabajo

Start by reading the Func::call and Func::call_async implementations and the component runtime event loop and fiber handling. Reproduce the supplied component example and inspect how its async function is called through the synchronous entry point. The issue leaves the design unresolved; done would require an agreed approach, such as deprecating Func::call, and tests covering the behavior.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

wasm-proposal:component-model-async

This program:

use wasmtime::component::{Component, Linker};
use wasmtime::{Engine, Store};

fn main() {
    let engine = Engine::default();
    let component = Component::new(
        &engine,
        r#"
(component
  (component $inner
    (core module $m
      (func (export "f") (param i32) (result i32)
        (i32.add (local.get 0) (i32.const 3))))
    (core instance $i (instantiate $m))
    (func (export "f") async (param "x" u32) (result u32)
      (canon lift (core func $i "f"))))
  (instance $inner (instantiate $inner))

  (core func $f (canon lower (func $inner "f")))
  (core module $m
    (import "" "f" (func $f (param i32) (result i32)))
    (func (export "run") (param i32) (result i32) (call $f (local.get 0))))
  (core instance $i (instantiate $m (with "" (instance (export "f" (func $f))))))
  (func (export "run") (param "x" u32) (result u32)
    (canon lift (core func $i "run")))
)
"#,
    )
    .unwrap();
    let mut store = Store::new(&engine, ());
    let instance = Linker::new(&engine).instantiate(&mut store, &component).unwrap();
    let run = instance
        .get_typed_func::<(u32,), (u32,)>(&mut store, "run")
        .unwrap();
    println!("{:?}", run.call(&mut store, (4,)));
}

currently yields:

$ cargo run
thread 'main' panicked at .../wasmtime-50.0.0/src/runtime/bug.rs:63:13:
BUG: Instance::start_call called without a running event loop

If call_async is used, however, this works fine. This is something where the spec has changed over time where originally we could rely on normal component model traps to ensure that Func::call pretty much worked as expected, but with recent spec changes it effectively requires the event loop to be running and to activate fibers and such.

In essence a synchronous entrypoint for component model functions is no longer really compatible with the component model spec definition. I don't know exactly how to thread this needle myself, but we may want to consider deprecating Func::call.

Lenguaje dominante
Rust
Estrellas
18.7k
Forks
1.9k
Merge medio
23 h
PR fusionados (30 d)
361

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  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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