Rust: async exported func cancel safety?

[SupernaviX]

Hello!

I'm contributing to a project which calls async wasmtime exports. Sometimes, those exported functions start failing with the error "wasm trap: cannot enter component instance". I think the issue might be that the generated wasm client isn't cancel-safe.

Here's the relevant snippet from the generated code (generated by wit-bindgen 0.38):

            let _enter = span.enter();
            let callee = unsafe {
                wasmtime::component::TypedFunc::<(u32, &Event,),(Result<Response,HandleError>,)>::new_unchecked(self.handle)
            };
            let(ret0,) = callee.call_async(store.as_context_mut(),(arg0,arg1,)).await?;
            callee.post_return_async(store.as_context_mut()).await?;
            Ok(ret0)

The docs say that if you call TypedFunc's call_async method, you must call post_return_async. In my codebase, the code path which invokes wasm can frequently get cancelled. If this snippet is cancelled during that call to call_async. then it looks like post_return_async will never be called (and there doesn't seem to be a way to recover from that).

Am I right that this code isn't cancel-safe? And if so, is there any way to recover from the cancellation?

[pchickey]

This wit-bindgen repo is for the project that generates guest language bindings for wit. It has a common providence as the version used in wasmtime, but this question is specific to the behavior of wasmtime-wit-bindgen. Could you please reopen this ticket in the wasmtime repo?

[SupernaviX]

Thank you! Opened bytecodealliance/wasmtime#10088 over there