wasmtime/runtime/component/
func.rs

1use crate::component::instance::Instance;
2use crate::component::matching::InstanceType;
3use crate::component::storage::storage_as_slice;
4use crate::component::types::Type;
5use crate::component::values::Val;
6use crate::prelude::*;
7use crate::runtime::vm::component::{ComponentInstance, InstanceFlags, ResourceTables};
8use crate::runtime::vm::{Export, VMFuncRef};
9use crate::store::StoreOpaque;
10use crate::{AsContext, AsContextMut, StoreContextMut, ValRaw};
11use anyhow::Context as _;
12use core::mem::{self, MaybeUninit};
13use core::ptr::NonNull;
14use wasmtime_environ::component::{
15    CanonicalOptions, ExportIndex, InterfaceType, MAX_FLAT_PARAMS, MAX_FLAT_RESULTS, TypeFuncIndex,
16    TypeTuple,
17};
18
19#[cfg(feature = "component-model-async")]
20use crate::component::concurrent::{self, AsAccessor, PreparedCall};
21
22mod host;
23mod options;
24mod typed;
25pub use self::host::*;
26pub use self::options::*;
27pub use self::typed::*;
28
29/// A WebAssembly component function which can be called.
30///
31/// This type is the dual of [`wasmtime::Func`](crate::Func) for component
32/// functions. An instance of [`Func`] represents a component function from a
33/// component [`Instance`](crate::component::Instance). Like with
34/// [`wasmtime::Func`](crate::Func) it's possible to call functions either
35/// synchronously or asynchronously and either typed or untyped.
36#[derive(Copy, Clone, Debug)]
37#[repr(C)] // here for the C API.
38pub struct Func {
39    instance: Instance,
40    index: ExportIndex,
41}
42
43// Double-check that the C representation in `component/instance.h` matches our
44// in-Rust representation here in terms of size/alignment/etc.
45const _: () = {
46    #[repr(C)]
47    struct T(u64, u32);
48    #[repr(C)]
49    struct C(T, u32);
50    assert!(core::mem::size_of::<C>() == core::mem::size_of::<Func>());
51    assert!(core::mem::align_of::<C>() == core::mem::align_of::<Func>());
52    assert!(core::mem::offset_of!(Func, instance) == 0);
53};
54
55impl Func {
56    pub(crate) fn from_lifted_func(instance: Instance, index: ExportIndex) -> Func {
57        Func { instance, index }
58    }
59
60    /// Attempt to cast this [`Func`] to a statically typed [`TypedFunc`] with
61    /// the provided `Params` and `Return`.
62    ///
63    /// This function will perform a type-check at runtime that the [`Func`]
64    /// takes `Params` as parameters and returns `Return`. If the type-check
65    /// passes then a [`TypedFunc`] will be returned which can be used to
66    /// invoke the function in an efficient, statically-typed, and ergonomic
67    /// manner.
68    ///
69    /// The `Params` type parameter here is a tuple of the parameters to the
70    /// function. A function which takes no arguments should use `()`, a
71    /// function with one argument should use `(T,)`, etc. Note that all
72    /// `Params` must also implement the [`Lower`] trait since they're going
73    /// into wasm.
74    ///
75    /// The `Return` type parameter is the return value of this function. A
76    /// return value of `()` means that there's no return (similar to a Rust
77    /// unit return) and otherwise a type `T` can be specified. Note that the
78    /// `Return` must also implement the [`Lift`] trait since it's coming from
79    /// wasm.
80    ///
81    /// Types specified here must implement the [`ComponentType`] trait. This
82    /// trait is implemented for built-in types to Rust such as integer
83    /// primitives, floats, `Option<T>`, `Result<T, E>`, strings, `Vec<T>`, and
84    /// more. As parameters you'll be passing native Rust types.
85    ///
86    /// See the documentation for [`ComponentType`] for more information about
87    /// supported types.
88    ///
89    /// # Errors
90    ///
91    /// If the function does not actually take `Params` as its parameters or
92    /// return `Return` then an error will be returned.
93    ///
94    /// # Panics
95    ///
96    /// This function will panic if `self` is not owned by the `store`
97    /// specified.
98    ///
99    /// # Examples
100    ///
101    /// Calling a function which takes no parameters and has no return value:
102    ///
103    /// ```
104    /// # use wasmtime::component::Func;
105    /// # use wasmtime::Store;
106    /// # fn foo(func: &Func, store: &mut Store<()>) -> anyhow::Result<()> {
107    /// let typed = func.typed::<(), ()>(&store)?;
108    /// typed.call(store, ())?;
109    /// # Ok(())
110    /// # }
111    /// ```
112    ///
113    /// Calling a function which takes one string parameter and returns a
114    /// string:
115    ///
116    /// ```
117    /// # use wasmtime::component::Func;
118    /// # use wasmtime::Store;
119    /// # fn foo(func: &Func, mut store: Store<()>) -> anyhow::Result<()> {
120    /// let typed = func.typed::<(&str,), (String,)>(&store)?;
121    /// let ret = typed.call(&mut store, ("Hello, ",))?.0;
122    /// println!("returned string was: {}", ret);
123    /// # Ok(())
124    /// # }
125    /// ```
126    ///
127    /// Calling a function which takes multiple parameters and returns a boolean:
128    ///
129    /// ```
130    /// # use wasmtime::component::Func;
131    /// # use wasmtime::Store;
132    /// # fn foo(func: &Func, mut store: Store<()>) -> anyhow::Result<()> {
133    /// let typed = func.typed::<(u32, Option<&str>, &[u8]), (bool,)>(&store)?;
134    /// let ok: bool = typed.call(&mut store, (1, Some("hello"), b"bytes!"))?.0;
135    /// println!("return value was: {ok}");
136    /// # Ok(())
137    /// # }
138    /// ```
139    pub fn typed<Params, Return>(&self, store: impl AsContext) -> Result<TypedFunc<Params, Return>>
140    where
141        Params: ComponentNamedList + Lower,
142        Return: ComponentNamedList + Lift,
143    {
144        self._typed(store.as_context().0, None)
145    }
146
147    pub(crate) fn _typed<Params, Return>(
148        &self,
149        store: &StoreOpaque,
150        instance: Option<&ComponentInstance>,
151    ) -> Result<TypedFunc<Params, Return>>
152    where
153        Params: ComponentNamedList + Lower,
154        Return: ComponentNamedList + Lift,
155    {
156        self.typecheck::<Params, Return>(store, instance)?;
157        unsafe { Ok(TypedFunc::new_unchecked(*self)) }
158    }
159
160    fn typecheck<Params, Return>(
161        &self,
162        store: &StoreOpaque,
163        instance: Option<&ComponentInstance>,
164    ) -> Result<()>
165    where
166        Params: ComponentNamedList + Lower,
167        Return: ComponentNamedList + Lift,
168    {
169        let cx = InstanceType::new(instance.unwrap_or_else(|| self.instance.id().get(store)));
170        let ty = &cx.types[self.ty(store)];
171
172        Params::typecheck(&InterfaceType::Tuple(ty.params), &cx)
173            .context("type mismatch with parameters")?;
174        Return::typecheck(&InterfaceType::Tuple(ty.results), &cx)
175            .context("type mismatch with results")?;
176
177        Ok(())
178    }
179
180    /// Get the parameter names and types for this function.
181    pub fn params(&self, store: impl AsContext) -> Box<[(String, Type)]> {
182        let store = store.as_context();
183        let instance = self.instance.id().get(store.0);
184        let types = instance.component().types();
185        let func_ty = &types[self.ty(store.0)];
186        types[func_ty.params]
187            .types
188            .iter()
189            .zip(&func_ty.param_names)
190            .map(|(ty, name)| (name.clone(), Type::from(ty, &InstanceType::new(instance))))
191            .collect()
192    }
193
194    /// Get the result types for this function.
195    pub fn results(&self, store: impl AsContext) -> Box<[Type]> {
196        let store = store.as_context();
197        let instance = self.instance.id().get(store.0);
198        let types = instance.component().types();
199        let ty = self.ty(store.0);
200        types[types[ty].results]
201            .types
202            .iter()
203            .map(|ty| Type::from(ty, &InstanceType::new(instance)))
204            .collect()
205    }
206
207    fn ty(&self, store: &StoreOpaque) -> TypeFuncIndex {
208        let instance = self.instance.id().get(store);
209        let (ty, _, _) = instance.component().export_lifted_function(self.index);
210        ty
211    }
212
213    /// Invokes this function with the `params` given and returns the result.
214    ///
215    /// The `params` provided must match the parameters that this function takes
216    /// in terms of their types and the number of parameters. Results will be
217    /// written to the `results` slice provided if the call completes
218    /// successfully. The initial types of the values in `results` are ignored
219    /// and values are overwritten to write the result. It's required that the
220    /// size of `results` exactly matches the number of results that this
221    /// function produces.
222    ///
223    /// Note that after a function is invoked the embedder needs to invoke
224    /// [`Func::post_return`] to execute any final cleanup required by the
225    /// guest. This function call is required to either call the function again
226    /// or to call another function.
227    ///
228    /// For more detailed information see the documentation of
229    /// [`TypedFunc::call`].
230    ///
231    /// # Errors
232    ///
233    /// Returns an error in situations including but not limited to:
234    ///
235    /// * `params` is not the right size or if the values have the wrong type
236    /// * `results` is not the right size
237    /// * A trap occurs while executing the function
238    /// * The function calls a host function which returns an error
239    ///
240    /// See [`TypedFunc::call`] for more information in addition to
241    /// [`wasmtime::Func::call`](crate::Func::call).
242    ///
243    /// # Panics
244    ///
245    /// Panics if this is called on a function in an asynchronous store. This
246    /// only works with functions defined within a synchronous store. Also
247    /// panics if `store` does not own this function.
248    pub fn call(
249        &self,
250        mut store: impl AsContextMut,
251        params: &[Val],
252        results: &mut [Val],
253    ) -> Result<()> {
254        let mut store = store.as_context_mut();
255        assert!(
256            !store.0.async_support(),
257            "must use `call_async` when async support is enabled on the config"
258        );
259        self.call_impl(&mut store.as_context_mut(), params, results)
260    }
261
262    /// Exactly like [`Self::call`] except for use on async stores.
263    ///
264    /// Note that after this [`Func::post_return_async`] will be used instead of
265    /// the synchronous version at [`Func::post_return`].
266    ///
267    /// # Panics
268    ///
269    /// Panics if this is called on a function in a synchronous store. This
270    /// only works with functions defined within an asynchronous store. Also
271    /// panics if `store` does not own this function.
272    #[cfg(feature = "async")]
273    pub async fn call_async(
274        &self,
275        mut store: impl AsContextMut<Data: Send>,
276        params: &[Val],
277        results: &mut [Val],
278    ) -> Result<()> {
279        let mut store = store.as_context_mut();
280
281        #[cfg(feature = "component-model-async")]
282        {
283            self.instance
284                .run_concurrent(&mut store, async |store| {
285                    self.call_concurrent_dynamic(store, params, results, false)
286                        .await
287                        .map(drop)
288                })
289                .await?
290        }
291        #[cfg(not(feature = "component-model-async"))]
292        {
293            assert!(
294                store.0.async_support(),
295                "cannot use `call_async` without enabling async support in the config"
296            );
297            store
298                .on_fiber(|store| self.call_impl(store, params, results))
299                .await?
300        }
301    }
302
303    fn check_params_results<T>(
304        &self,
305        store: StoreContextMut<T>,
306        params: &[Val],
307        results: &mut [Val],
308    ) -> Result<()> {
309        let param_tys = self.params(&store);
310        if param_tys.len() != params.len() {
311            bail!(
312                "expected {} argument(s), got {}",
313                param_tys.len(),
314                params.len(),
315            );
316        }
317
318        let result_tys = self.results(&store);
319
320        if result_tys.len() != results.len() {
321            bail!(
322                "expected {} result(s), got {}",
323                result_tys.len(),
324                results.len(),
325            );
326        }
327
328        Ok(())
329    }
330
331    /// Start a concurrent call to this function.
332    ///
333    /// Unlike [`Self::call`] and [`Self::call_async`] (both of which require
334    /// exclusive access to the store until the completion of the call), calls
335    /// made using this method may run concurrently with other calls to the same
336    /// instance.  In addition, the runtime will call the `post-return` function
337    /// (if any) automatically when the guest task completes -- no need to
338    /// explicitly call `Func::post_return` afterward.
339    ///
340    /// This returns a [`TaskExit`] representing the completion of the guest
341    /// task and any transitive subtasks it might create.
342    ///
343    /// # Panics
344    ///
345    /// Panics if the store that the [`Accessor`] is derived from does not own
346    /// this function.
347    #[cfg(feature = "component-model-async")]
348    pub async fn call_concurrent(
349        self,
350        accessor: impl AsAccessor<Data: Send>,
351        params: &[Val],
352        results: &mut [Val],
353    ) -> Result<TaskExit> {
354        self.call_concurrent_dynamic(accessor, params, results, true)
355            .await
356    }
357
358    /// Internal helper function for `call_async` and `call_concurrent`.
359    #[cfg(feature = "component-model-async")]
360    async fn call_concurrent_dynamic(
361        self,
362        accessor: impl AsAccessor<Data: Send>,
363        params: &[Val],
364        results: &mut [Val],
365        call_post_return_automatically: bool,
366    ) -> Result<TaskExit> {
367        let result = accessor.as_accessor().with(|mut store| {
368            assert!(
369                store.as_context_mut().0.async_support(),
370                "cannot use `call_concurrent` when async support is not enabled on the config"
371            );
372            self.check_params_results(store.as_context_mut(), params, results)?;
373            let prepared = self.prepare_call_dynamic(
374                store.as_context_mut(),
375                params.to_vec(),
376                call_post_return_automatically,
377            )?;
378            concurrent::queue_call(store.as_context_mut(), prepared)
379        })?;
380
381        let (run_results, rx) = result.await?;
382        assert_eq!(run_results.len(), results.len());
383        for (result, slot) in run_results.into_iter().zip(results) {
384            *slot = result;
385        }
386        Ok(TaskExit(rx))
387    }
388
389    /// Calls `concurrent::prepare_call` with monomorphized functions for
390    /// lowering the parameters and lifting the result.
391    #[cfg(feature = "component-model-async")]
392    fn prepare_call_dynamic<'a, T: Send + 'static>(
393        self,
394        mut store: StoreContextMut<'a, T>,
395        params: Vec<Val>,
396        call_post_return_automatically: bool,
397    ) -> Result<PreparedCall<Vec<Val>>> {
398        let store = store.as_context_mut();
399
400        concurrent::prepare_call(
401            store,
402            self,
403            MAX_FLAT_PARAMS,
404            true,
405            call_post_return_automatically,
406            move |func, store, params_out| {
407                func.with_lower_context(store, call_post_return_automatically, |cx, ty| {
408                    Self::lower_args(cx, &params, ty, params_out)
409                })
410            },
411            move |func, store, results| {
412                let max_flat = if func.abi_async(store) {
413                    MAX_FLAT_PARAMS
414                } else {
415                    MAX_FLAT_RESULTS
416                };
417                let results = func.with_lift_context(store, |cx, ty| {
418                    Self::lift_results(cx, ty, results, max_flat)?.collect::<Result<Vec<_>>>()
419                })?;
420                Ok(Box::new(results))
421            },
422        )
423    }
424
425    fn call_impl(
426        &self,
427        mut store: impl AsContextMut,
428        params: &[Val],
429        results: &mut [Val],
430    ) -> Result<()> {
431        let mut store = store.as_context_mut();
432
433        self.check_params_results(store.as_context_mut(), params, results)?;
434
435        if self.abi_async(store.0) {
436            unreachable!(
437                "async-lifted exports should have failed validation \
438                 when `component-model-async` feature disabled"
439            );
440        }
441
442        // SAFETY: the chosen representations of type parameters to `call_raw`
443        // here should be generally safe to work with:
444        //
445        // * parameters use `MaybeUninit<[MaybeUninit<ValRaw>; MAX_FLAT_PARAMS]>`
446        //   which represents the maximal possible number of parameters that can
447        //   be passed to lifted component functions. This is modeled with
448        //   `MaybeUninit` to represent how it all starts as uninitialized and
449        //   thus can't be safely read during lowering.
450        //
451        // * results are modeled as `[ValRaw; MAX_FLAT_RESULTS]` which
452        //   represents the maximal size of values that can be returned. Note
453        //   that if the function doesn't actually have a return value then the
454        //   `ValRaw` inside the array will have undefined contents. That is
455        //   safe in Rust, however, due to `ValRaw` being a `union`. The
456        //   contents should dynamically not be read due to the type of the
457        //   function used here matching the actual lift.
458        unsafe {
459            self.call_raw(
460                store,
461                |cx, ty, dst: &mut MaybeUninit<[MaybeUninit<ValRaw>; MAX_FLAT_PARAMS]>| {
462                    // SAFETY: it's safe to assume that
463                    // `MaybeUninit<array-of-maybe-uninit>` is initialized because
464                    // each individual element is still considered uninitialized.
465                    let dst: &mut [MaybeUninit<ValRaw>] = dst.assume_init_mut();
466                    Self::lower_args(cx, params, ty, dst)
467                },
468                |cx, results_ty, src: &[ValRaw; MAX_FLAT_RESULTS]| {
469                    let max_flat = MAX_FLAT_RESULTS;
470                    for (result, slot) in
471                        Self::lift_results(cx, results_ty, src, max_flat)?.zip(results)
472                    {
473                        *slot = result?;
474                    }
475                    Ok(())
476                },
477            )
478        }
479    }
480
481    pub(crate) fn lifted_core_func(&self, store: &mut StoreOpaque) -> NonNull<VMFuncRef> {
482        let def = {
483            let instance = self.instance.id().get(store);
484            let (_ty, def, _options) = instance.component().export_lifted_function(self.index);
485            def.clone()
486        };
487        match self.instance.lookup_vmdef(store, &def) {
488            Export::Function(f) => f.vm_func_ref(store),
489            _ => unreachable!(),
490        }
491    }
492
493    pub(crate) fn post_return_core_func(&self, store: &StoreOpaque) -> Option<NonNull<VMFuncRef>> {
494        let instance = self.instance.id().get(store);
495        let component = instance.component();
496        let (_ty, _def, options) = component.export_lifted_function(self.index);
497        let post_return = component.env_component().options[options].post_return;
498        post_return.map(|i| instance.runtime_post_return(i))
499    }
500
501    pub(crate) fn abi_async(&self, store: &StoreOpaque) -> bool {
502        let instance = self.instance.id().get(store);
503        let component = instance.component();
504        let (_ty, _def, options) = component.export_lifted_function(self.index);
505        component.env_component().options[options].async_
506    }
507
508    pub(crate) fn abi_info<'a>(
509        &self,
510        store: &'a StoreOpaque,
511    ) -> (Options, InstanceFlags, TypeFuncIndex, &'a CanonicalOptions) {
512        let vminstance = self.instance.id().get(store);
513        let component = vminstance.component();
514        let (ty, _def, options_index) = component.export_lifted_function(self.index);
515        let raw_options = &component.env_component().options[options_index];
516        let options = Options::new_index(store, self.instance, options_index);
517        (
518            options,
519            vminstance.instance_flags(raw_options.instance),
520            ty,
521            raw_options,
522        )
523    }
524
525    /// Invokes the underlying wasm function, lowering arguments and lifting the
526    /// result.
527    ///
528    /// The `lower` function and `lift` function provided here are what actually
529    /// do the lowering and lifting. The `LowerParams` and `LowerReturn` types
530    /// are what will be allocated on the stack for this function call. They
531    /// should be appropriately sized for the lowering/lifting operation
532    /// happening.
533    ///
534    /// # Safety
535    ///
536    /// The safety of this function relies on the correct definitions of the
537    /// `LowerParams` and `LowerReturn` type. They must match the type of `self`
538    /// for the params/results that are going to be produced. Additionally
539    /// these types must be representable with a sequence of `ValRaw` values.
540    unsafe fn call_raw<T, Return, LowerParams, LowerReturn>(
541        &self,
542        mut store: StoreContextMut<'_, T>,
543        lower: impl FnOnce(
544            &mut LowerContext<'_, T>,
545            InterfaceType,
546            &mut MaybeUninit<LowerParams>,
547        ) -> Result<()>,
548        lift: impl FnOnce(&mut LiftContext<'_>, InterfaceType, &LowerReturn) -> Result<Return>,
549    ) -> Result<Return>
550    where
551        LowerParams: Copy,
552        LowerReturn: Copy,
553    {
554        let export = self.lifted_core_func(store.0);
555
556        #[repr(C)]
557        union Union<Params: Copy, Return: Copy> {
558            params: Params,
559            ret: Return,
560        }
561
562        let space = &mut MaybeUninit::<Union<LowerParams, LowerReturn>>::uninit();
563
564        // Double-check the size/alignment of `space`, just in case.
565        //
566        // Note that this alone is not enough to guarantee the validity of the
567        // `unsafe` block below, but it's definitely required. In any case LLVM
568        // should be able to trivially see through these assertions and remove
569        // them in release mode.
570        let val_size = mem::size_of::<ValRaw>();
571        let val_align = mem::align_of::<ValRaw>();
572        assert!(mem::size_of_val(space) % val_size == 0);
573        assert!(mem::size_of_val(map_maybe_uninit!(space.params)) % val_size == 0);
574        assert!(mem::size_of_val(map_maybe_uninit!(space.ret)) % val_size == 0);
575        assert!(mem::align_of_val(space) == val_align);
576        assert!(mem::align_of_val(map_maybe_uninit!(space.params)) == val_align);
577        assert!(mem::align_of_val(map_maybe_uninit!(space.ret)) == val_align);
578
579        self.with_lower_context(store.as_context_mut(), false, |cx, ty| {
580            cx.enter_call();
581            lower(cx, ty, map_maybe_uninit!(space.params))
582        })?;
583
584        // SAFETY: We are providing the guarantee that all the inputs are valid.
585        // The various pointers passed in for the function are all valid since
586        // they're coming from our store, and the `params_and_results` should
587        // have the correct layout for the core wasm function we're calling.
588        // Note that this latter point relies on the correctness of this module
589        // and `ComponentType` implementations, hence `ComponentType` being an
590        // `unsafe` trait.
591        unsafe {
592            crate::Func::call_unchecked_raw(
593                &mut store,
594                export,
595                NonNull::new(core::ptr::slice_from_raw_parts_mut(
596                    space.as_mut_ptr().cast(),
597                    mem::size_of_val(space) / mem::size_of::<ValRaw>(),
598                ))
599                .unwrap(),
600            )?;
601        }
602
603        // SAFETY: We're relying on the correctness of the structure of
604        // `LowerReturn` and the type-checking performed to acquire the
605        // `TypedFunc` to make this safe. It should be the case that
606        // `LowerReturn` is the exact representation of the return value when
607        // interpreted as `[ValRaw]`, and additionally they should have the
608        // correct types for the function we just called (which filled in the
609        // return values).
610        let ret: &LowerReturn = unsafe { map_maybe_uninit!(space.ret).assume_init_ref() };
611
612        // Lift the result into the host while managing post-return state
613        // here as well.
614        //
615        // After a successful lift the return value of the function, which
616        // is currently required to be 0 or 1 values according to the
617        // canonical ABI, is saved within the `Store`'s `FuncData`. This'll
618        // later get used in post-return.
619        // flags.set_needs_post_return(true);
620        let val = self.with_lift_context(store.0, |cx, ty| lift(cx, ty, ret))?;
621
622        // SAFETY: it's a contract of this function that `LowerReturn` is an
623        // appropriate representation of the result of this function.
624        let ret_slice = unsafe { storage_as_slice(ret) };
625
626        self.instance.id().get_mut(store.0).post_return_arg_set(
627            self.index,
628            match ret_slice.len() {
629                0 => ValRaw::i32(0),
630                1 => ret_slice[0],
631                _ => unreachable!(),
632            },
633        );
634        return Ok(val);
635    }
636
637    /// Invokes the `post-return` canonical ABI option, if specified, after a
638    /// [`Func::call`] has finished.
639    ///
640    /// This function is a required method call after a [`Func::call`] completes
641    /// successfully. After the embedder has finished processing the return
642    /// value then this function must be invoked.
643    ///
644    /// # Errors
645    ///
646    /// This function will return an error in the case of a WebAssembly trap
647    /// happening during the execution of the `post-return` function, if
648    /// specified.
649    ///
650    /// # Panics
651    ///
652    /// This function will panic if it's not called under the correct
653    /// conditions. This can only be called after a previous invocation of
654    /// [`Func::call`] completes successfully, and this function can only
655    /// be called for the same [`Func`] that was `call`'d.
656    ///
657    /// If this function is called when [`Func::call`] was not previously
658    /// called, then it will panic. If a different [`Func`] for the same
659    /// component instance was invoked then this function will also panic
660    /// because the `post-return` needs to happen for the other function.
661    ///
662    /// Panics if this is called on a function in an asynchronous store.
663    /// This only works with functions defined within a synchronous store.
664    #[inline]
665    pub fn post_return(&self, mut store: impl AsContextMut) -> Result<()> {
666        let store = store.as_context_mut();
667        assert!(
668            !store.0.async_support(),
669            "must use `post_return_async` when async support is enabled on the config"
670        );
671        self.post_return_impl(store)
672    }
673
674    /// Exactly like [`Self::post_return`] except for use on async stores.
675    ///
676    /// # Panics
677    ///
678    /// Panics if this is called on a function in a synchronous store. This
679    /// only works with functions defined within an asynchronous store.
680    #[cfg(feature = "async")]
681    pub async fn post_return_async(&self, mut store: impl AsContextMut<Data: Send>) -> Result<()> {
682        let mut store = store.as_context_mut();
683        assert!(
684            store.0.async_support(),
685            "cannot use `post_return_async` without enabling async support in the config"
686        );
687        // Future optimization opportunity: conditionally use a fiber here since
688        // some func's post_return will not need the async context (i.e. end up
689        // calling async host functionality)
690        store.on_fiber(|store| self.post_return_impl(store)).await?
691    }
692
693    fn post_return_impl(&self, mut store: impl AsContextMut) -> Result<()> {
694        let mut store = store.as_context_mut();
695
696        let index = self.index;
697        let vminstance = self.instance.id().get(store.0);
698        let component = vminstance.component();
699        let (_ty, _def, options) = component.export_lifted_function(index);
700        let post_return = self.post_return_core_func(store.0);
701        let mut flags =
702            vminstance.instance_flags(component.env_component().options[options].instance);
703        let mut instance = self.instance.id().get_mut(store.0);
704        let post_return_arg = instance.as_mut().post_return_arg_take(index);
705
706        unsafe {
707            // First assert that the instance is in a "needs post return" state.
708            // This will ensure that the previous action on the instance was a
709            // function call above. This flag is only set after a component
710            // function returns so this also can't be called (as expected)
711            // during a host import for example.
712            //
713            // Note, though, that this assert is not sufficient because it just
714            // means some function on this instance needs its post-return
715            // called. We need a precise post-return for a particular function
716            // which is the second assert here (the `.expect`). That will assert
717            // that this function itself needs to have its post-return called.
718            //
719            // The theory at least is that these two asserts ensure component
720            // model semantics are upheld where the host properly calls
721            // `post_return` on the right function despite the call being a
722            // separate step in the API.
723            assert!(
724                flags.needs_post_return(),
725                "post_return can only be called after a function has previously been called",
726            );
727            let post_return_arg = post_return_arg.expect("calling post_return on wrong function");
728
729            // This is a sanity-check assert which shouldn't ever trip.
730            assert!(!flags.may_enter());
731
732            // Unset the "needs post return" flag now that post-return is being
733            // processed. This will cause future invocations of this method to
734            // panic, even if the function call below traps.
735            flags.set_needs_post_return(false);
736
737            // Post return functions are forbidden from calling imports or
738            // intrinsics.
739            flags.set_may_leave(false);
740
741            // If the function actually had a `post-return` configured in its
742            // canonical options that's executed here.
743            //
744            // Note that if this traps (returns an error) this function
745            // intentionally leaves the instance in a "poisoned" state where it
746            // can no longer be entered because `may_enter` is `false`.
747            if let Some(func) = post_return {
748                crate::Func::call_unchecked_raw(
749                    &mut store,
750                    func,
751                    NonNull::new(core::ptr::slice_from_raw_parts(&post_return_arg, 1).cast_mut())
752                        .unwrap(),
753                )?;
754            }
755
756            // And finally if everything completed successfully then the "may
757            // enter" and "may leave" flags are set to `true` again here which
758            // enables further use of the component.
759            flags.set_may_enter(true);
760            flags.set_may_leave(true);
761
762            let (calls, host_table, _, instance) = store
763                .0
764                .component_resource_state_with_instance(self.instance);
765            ResourceTables {
766                host_table: Some(host_table),
767                calls,
768                guest: Some(instance.guest_tables()),
769            }
770            .exit_call()?;
771        }
772        Ok(())
773    }
774
775    fn lower_args<T>(
776        cx: &mut LowerContext<'_, T>,
777        params: &[Val],
778        params_ty: InterfaceType,
779        dst: &mut [MaybeUninit<ValRaw>],
780    ) -> Result<()> {
781        let params_ty = match params_ty {
782            InterfaceType::Tuple(i) => &cx.types[i],
783            _ => unreachable!(),
784        };
785        if params_ty.abi.flat_count(MAX_FLAT_PARAMS).is_some() {
786            let dst = &mut dst.iter_mut();
787
788            params
789                .iter()
790                .zip(params_ty.types.iter())
791                .try_for_each(|(param, ty)| param.lower(cx, *ty, dst))
792        } else {
793            Self::store_args(cx, &params_ty, params, dst)
794        }
795    }
796
797    fn store_args<T>(
798        cx: &mut LowerContext<'_, T>,
799        params_ty: &TypeTuple,
800        args: &[Val],
801        dst: &mut [MaybeUninit<ValRaw>],
802    ) -> Result<()> {
803        let size = usize::try_from(params_ty.abi.size32).unwrap();
804        let ptr = cx.realloc(0, 0, params_ty.abi.align32, size)?;
805        let mut offset = ptr;
806        for (ty, arg) in params_ty.types.iter().zip(args) {
807            let abi = cx.types.canonical_abi(ty);
808            arg.store(cx, *ty, abi.next_field32_size(&mut offset))?;
809        }
810
811        dst[0].write(ValRaw::i64(ptr as i64));
812
813        Ok(())
814    }
815
816    fn lift_results<'a, 'b>(
817        cx: &'a mut LiftContext<'b>,
818        results_ty: InterfaceType,
819        src: &'a [ValRaw],
820        max_flat: usize,
821    ) -> Result<Box<dyn Iterator<Item = Result<Val>> + 'a>> {
822        let results_ty = match results_ty {
823            InterfaceType::Tuple(i) => &cx.types[i],
824            _ => unreachable!(),
825        };
826        if results_ty.abi.flat_count(max_flat).is_some() {
827            let mut flat = src.iter();
828            Ok(Box::new(
829                results_ty
830                    .types
831                    .iter()
832                    .map(move |ty| Val::lift(cx, *ty, &mut flat)),
833            ))
834        } else {
835            let iter = Self::load_results(cx, results_ty, &mut src.iter())?;
836            Ok(Box::new(iter))
837        }
838    }
839
840    fn load_results<'a, 'b>(
841        cx: &'a mut LiftContext<'b>,
842        results_ty: &'a TypeTuple,
843        src: &mut core::slice::Iter<'_, ValRaw>,
844    ) -> Result<impl Iterator<Item = Result<Val>> + use<'a, 'b>> {
845        // FIXME(#4311): needs to read an i64 for memory64
846        let ptr = usize::try_from(src.next().unwrap().get_u32())?;
847        if ptr % usize::try_from(results_ty.abi.align32)? != 0 {
848            bail!("return pointer not aligned");
849        }
850
851        let bytes = cx
852            .memory()
853            .get(ptr..)
854            .and_then(|b| b.get(..usize::try_from(results_ty.abi.size32).unwrap()))
855            .ok_or_else(|| anyhow::anyhow!("pointer out of bounds of memory"))?;
856
857        let mut offset = 0;
858        Ok(results_ty.types.iter().map(move |ty| {
859            let abi = cx.types.canonical_abi(ty);
860            let offset = abi.next_field32_size(&mut offset);
861            Val::load(cx, *ty, &bytes[offset..][..abi.size32 as usize])
862        }))
863    }
864
865    #[cfg(feature = "component-model-async")]
866    pub(crate) fn instance(self) -> Instance {
867        self.instance
868    }
869
870    #[cfg(feature = "component-model-async")]
871    pub(crate) fn index(self) -> ExportIndex {
872        self.index
873    }
874
875    /// Creates a `LowerContext` using the configuration values of this lifted
876    /// function.
877    ///
878    /// The `lower` closure provided should perform the actual lowering and
879    /// return the result of the lowering operation which is then returned from
880    /// this function as well.
881    fn with_lower_context<T>(
882        self,
883        mut store: StoreContextMut<T>,
884        may_enter: bool,
885        lower: impl FnOnce(&mut LowerContext<T>, InterfaceType) -> Result<()>,
886    ) -> Result<()> {
887        let types = self.instance.id().get(store.0).component().types().clone();
888        let (options, mut flags, ty, _) = self.abi_info(store.0);
889
890        // Test the "may enter" flag which is a "lock" on this instance.
891        // This is immediately set to `false` afterwards and note that
892        // there's no on-cleanup setting this flag back to true. That's an
893        // intentional design aspect where if anything goes wrong internally
894        // from this point on the instance is considered "poisoned" and can
895        // never be entered again. The only time this flag is set to `true`
896        // again is after post-return logic has completed successfully.
897        unsafe {
898            if !flags.may_enter() {
899                bail!(crate::Trap::CannotEnterComponent);
900            }
901            flags.set_may_enter(false);
902        }
903
904        // Perform the actual lowering, where while this is running the
905        // component is forbidden from calling imports.
906        unsafe {
907            debug_assert!(flags.may_leave());
908            flags.set_may_leave(false);
909        }
910        let mut cx = LowerContext::new(store.as_context_mut(), &options, &types, self.instance);
911        let result = lower(&mut cx, InterfaceType::Tuple(types[ty].params));
912        unsafe { flags.set_may_leave(true) };
913        result?;
914
915        // If this is an async function and `may_enter == true` then we're
916        // allowed to reenter the component at this point, and otherwise flag a
917        // post-return call being required as we're about to enter wasm and
918        // afterwards need a post-return.
919        unsafe {
920            if may_enter && options.async_() {
921                flags.set_may_enter(true);
922            } else {
923                flags.set_needs_post_return(true);
924            }
925        }
926
927        Ok(())
928    }
929
930    /// Creates a `LiftContext` using the configuration values with this lifted
931    /// function.
932    ///
933    /// The closure `lift` provided should actually perform the lift itself and
934    /// the result of that closure is returned from this function call as well.
935    fn with_lift_context<R>(
936        self,
937        store: &mut StoreOpaque,
938        lift: impl FnOnce(&mut LiftContext, InterfaceType) -> Result<R>,
939    ) -> Result<R> {
940        let (options, _flags, ty, _) = self.abi_info(store);
941        let mut cx = LiftContext::new(store, &options, self.instance);
942        let ty = InterfaceType::Tuple(cx.types[ty].results);
943        lift(&mut cx, ty)
944    }
945}
946
947/// Represents the completion of a task created using
948/// `[Typed]Func::call_concurrent`.
949///
950/// In general, a guest task may continue running after returning a value.
951/// Moreover, any given guest task may create its own subtasks before or after
952/// returning and may exit before some or all of those subtasks have finished
953/// running.  In that case, the still-running subtasks will be "reparented" to
954/// the nearest surviving caller, which may be the original host call.  The
955/// future returned by `TaskExit::block` will resolve once all transitive
956/// subtasks created directly or indirectly by the original call to
957/// `Instance::call_concurrent` have exited.
958#[cfg(feature = "component-model-async")]
959pub struct TaskExit(futures::channel::oneshot::Receiver<()>);
960
961#[cfg(feature = "component-model-async")]
962impl TaskExit {
963    /// Returns a future which will resolve once all transitive subtasks created
964    /// directly or indirectly by the original call to
965    /// `Instance::call_concurrent` have exited.
966    pub async fn block(self, accessor: impl AsAccessor<Data: Send>) {
967        // The current implementation makes no use of `accessor`, but future
968        // implementations might (e.g. by using a more efficient mechanism than
969        // a oneshot channel).
970        _ = accessor;
971
972        // We don't care whether the sender sent us a value or was dropped
973        // first; either one counts as a notification, so we ignore the result
974        // once the future resolves:
975        _ = self.0.await;
976    }
977}