Stream: git-wasmtime

Topic: wasmtime / issue #14576 Internal `do_no_suspend` flag not...

Wasmtime GitHub notifications bot (Oct 06 2026 at 16:59):

alexcrichton opened issue #14576:

The current handling of do_not_suspend relies on stack-like behavior of sync tasks (LIFO) but recent spec changes means that this is no longer a guarantee. For example this test I believe should pass:

#[tokio::test]
#[cfg_attr(miri, ignore)]
async fn concurrent_sync_typed_calls_with_yield() -> Result<()> {
    let engine = Engine::default();
    let component = Component::new(
        &engine,
        r#"
(component
  (core func $thread.yield (canon thread.yield))
  (core func $task.return (canon task.return))
  (core module $m
    (import "" "thread.yield" (func $yield (result i32)))
    (import "" "task.return" (func $task.return))
    (global $s1-running (mut i32) (i32.const 0))
    (func (export "s1")
      (global.set $s1-running (i32.const 1))
      (drop (call $yield))
      (global.set $s1-running (i32.const 0)))
    (func (export "s2")
      (if (global.get $s1-running) (then unreachable))
      (drop (call $yield)))
    (func (export "noop") (result i32) (call $task.return) (i32.const 0)) ;; EXIT
    (func (export "cb") (param i32 i32 i32) (result i32) unreachable))
  (core instance $i (instantiate $m (with "" (instance
    (export "thread.yield" (func $thread.yield))
    (export "task.return" (func $task.return))))))
  (func (export "s1") (canon lift (core func $i "s1")))
  (func (export "s2") (canon lift (core func $i "s2")))
  (func (export "noop") async
    (canon lift (core func $i "noop") async (callback (core func $i "cb"))))
)
        "#,
    )?;
    let mut store = Store::new(&engine, ());
    let instance = Linker::new(&engine)
        .instantiate_async(&mut store, &component)
        .await?;
    let s1 = instance.get_typed_func::<(), ()>(&mut store, "s1")?;
    let s2 = instance.get_typed_func::<(), ()>(&mut store, "s2")?;
    let noop = instance.get_typed_func::<(), ()>(&mut store, "noop")?;

    store
        .run_concurrent(async |accessor| {
            futures::future::try_join(
                s1.call_concurrent(accessor, ()),
                s2.call_concurrent(accessor, ()),
            )
            .await
        })
        .await??;

    store
        .run_concurrent(async |accessor| noop.call_concurrent(accessor, ()).await
        .await??;

    Ok(())
}

but it currently traps.

More wast tests, and an LLM summary if useful, can be found at https://gist.github.com/alexcrichton/6ff5e1688251f5988efca3fc9a83c705

Wasmtime GitHub notifications bot (Oct 06 2026 at 16:59):

alexcrichton added the wasm-proposal:component-model-async label to Issue #14576.

Wasmtime GitHub notifications bot (Oct 06 2026 at 18:32):

alexcrichton commented on issue #14576:

A related issue is that right now the runtime will only run sibling threads for a blocked sync task on the first switch, but after that it'll run anything. This is I believe all safe and sound and fine, but spec-incorrect. Some LLM details/summary is at https://gist.github.com/alexcrichton/26e1f262bfda51ab286765985184001d

Wasmtime GitHub notifications bot (Oct 08 2026 at 16:51):

fitzgen added the bug label to Issue #14576.

Last updated: Oct 11 2026 at 04:10 UTC