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Refactor away the Instantiator type in Wasmtime (#3972)

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* Refactor away the `Instantiator` type in Wasmtime

This internal type in Wasmtime was primarily used for the module linking
proposal to handle instantiation of many instances and refactor out the
sync and async parts to minimize duplication. With the removal of the
module linking proposal, however, this type isn't really necessary any
longer. In working to implement the component model proposal I was
looking already to refactor this and I figured it'd be good to land that
ahead of time on `main` separate of other refactorings.

This commit removes the `Instantiator` type in the `instance` module.
The type was already private to Wasmtime so this shouldn't have any
impact on consumers. This allows simplifying various code paths to avoid
another abstraction. The meat of instantiation is moved to
`Instance::new_raw` which should be reusable for the component model as
well.

One bug is actually fixed in this commit as well where
`Linker::instantiate` and `InstancePre::instantiate` failed to check
that async support was disabled on a store. This means that they could
have led to a panic if used with an async store and a start function
called an async import (or an async resource limiter yielded). A few
tests were updated with this.

* Review comments
This commit is contained in:
Alex Crichton
2022-04-05 10:35:00 -05:00
committed by GitHub
parent 78a595ac88
commit 011d2e1faa
4 changed files with 282 additions and 302 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
RELEASES.md
View File

@@ -19,6 +19,12 @@ Unreleased.
* Support for epoch-based interruption has been added to the C API.
[#3925](https://github.com/bytecodealliance/wasmtime/pull/3925)
### Fixed
* Using `InstancePre::instantiate` or `Linker::instantiate` will now panic as
intended when used with an async-configured `Store`.
[#TODO](https://github.com/bytecodealliance/wasmtime/pull/TODO)
### Removed
* Support for `Config::interruptable` and `InterruptHandle` has been removed

547
crates/wasmtime/src/instance.rs
View File

@@ -103,19 +103,12 @@ impl Instance {
module: &Module,
imports: &[Extern],
) -> Result<Instance, Error> {
// This unsafety comes from `Instantiator::new` where we must typecheck
// first, which we are sure to do here.
let mut store = store.as_context_mut();
let mut i = unsafe {
typecheck_externs(store.0, module, imports)?;
Instantiator::new(store.0, module, ImportSource::Externs(imports))?
};
assert!(
!store.0.async_support(),
"cannot use `new` when async support is enabled on the config"
);
i.run(&mut store)
let imports = Instance::typecheck_externs(store.0, module, imports)?;
// Note that the unsafety here should be satisfied by the call to
// `typecheck_externs` above which satisfies the condition that all
// the imports are valid for this module.
unsafe { Instance::new_started(&mut store, module, imports.as_ref()) }
}
/// Same as [`Instance::new`], except for usage in [asynchronous stores].
@@ -145,26 +138,222 @@ impl Instance {
where
T: Send,
{
// See `new` for unsafety comments
let mut store = store.as_context_mut();
let mut i = unsafe {
typecheck_externs(store.0, module, imports)?;
Instantiator::new(store.0, module, ImportSource::Externs(imports))?
};
let mut store = store.as_context_mut();
let imports = Instance::typecheck_externs(store.0, module, imports)?;
// See `new` for notes on this unsafety
unsafe { Instance::new_started_async(&mut store, module, imports.as_ref()).await }
}
fn typecheck_externs(
store: &mut StoreOpaque,
module: &Module,
imports: &[Extern],
) -> Result<OwnedImports> {
for import in imports {
if !import.comes_from_same_store(store) {
bail!("cross-`Store` instantiation is not currently supported");
}
}
typecheck(store, module, imports, |cx, ty, item| cx.extern_(ty, item))?;
let mut owned_imports = OwnedImports::new(module);
for import in imports {
owned_imports.push(import, store);
}
Ok(owned_imports)
}
/// Internal function to create an instance and run the start function.
///
/// This function's unsafety is the same as `Instance::new_raw`.
unsafe fn new_started<T>(
store: &mut StoreContextMut<'_, T>,
module: &Module,
imports: Imports<'_>,
) -> Result<Instance> {
assert!(
!store.0.async_support(),
"must use async instantiation when async support is enabled",
);
let (instance, start) = Instance::new_raw(store.0, module, imports)?;
if let Some(start) = start {
instance.start_raw(store, start)?;
}
Ok(instance)
}
/// Internal function to create an instance and run the start function.
///
/// This function's unsafety is the same as `Instance::new_raw`.
#[cfg(feature = "async")]
async unsafe fn new_started_async<T>(
store: &mut StoreContextMut<'_, T>,
module: &Module,
imports: Imports<'_>,
) -> Result<Instance>
where
T: Send,
{
// Note that the body of this function is intentionally quite similar
// to the `new_started` function, and it's intended that the two bodies
// here are small enough to be ok duplicating.
assert!(
store.0.async_support(),
"cannot use `new_async` without enabling async support on the config"
"must use sync instantiation when async support is disabled",
);
store
.on_fiber(|store| i.run(&mut store.as_context_mut()))
.on_fiber(|store| {
let (instance, start) = Instance::new_raw(store.0, module, imports)?;
if let Some(start) = start {
instance.start_raw(store, start)?;
}
Ok(instance)
})
.await?
}
/// Internal function to create an instance which doesn't have its `start`
/// function run yet.
///
/// This is not intended to be exposed from Wasmtime, it's intended to
/// refactor out common code from `new_started` and `new_started_async`.
///
/// Note that this step needs to be run on a fiber in async mode even
/// though it doesn't do any blocking work because an async resource
/// limiter may need to yield.
///
/// # Unsafety
///
/// This method is unsafe because it does not type-check the `imports`
/// provided. The `imports` provided must be suitable for the module
/// provided as well.
unsafe fn new_raw(
store: &mut StoreOpaque,
module: &Module,
imports: Imports<'_>,
) -> Result<(Instance, Option<FuncIndex>)> {
if !Engine::same(store.engine(), module.engine()) {
bail!("cross-`Engine` instantiation is not currently supported");
}
store.bump_resource_counts(module)?;
let compiled_module = module.compiled_module();
// Register the module just before instantiation to ensure we keep the module
// properly referenced while in use by the store.
store.modules_mut().register(module);
// The first thing we do is issue an instance allocation request
// to the instance allocator. This, on success, will give us an
// instance handle.
//
// Note that the `host_state` here is a pointer back to the
// `Instance` we'll be returning from this function. This is a
// circular reference so we can't construct it before we construct
// this instance, so we determine what the ID is and then assert
// it's the same later when we do actually insert it.
let instance_to_be = store.store_data().next_id::<InstanceData>();
let mut instance_handle =
store
.engine()
.allocator()
.allocate(InstanceAllocationRequest {
runtime_info: &module.runtime_info(),
imports,
host_state: Box::new(Instance(instance_to_be)),
store: StorePtr::new(store.traitobj()),
})?;
// The instance still has lots of setup, for example
// data/elements/start/etc. This can all fail, but even on failure
// the instance may persist some state via previous successful
// initialization. For this reason once we have an instance handle
// we immediately insert it into the store to keep it alive.
//
// Note that we `clone` the instance handle just to make easier
// working the the borrow checker here easier. Technically the `&mut
// instance` has somewhat of a borrow on `store` (which
// conflicts with the borrow on `store.engine`) but this doesn't
// matter in practice since initialization isn't even running any
// code here anyway.
let id = store.add_instance(instance_handle.clone(), false);
// Additionally, before we start doing fallible instantiation, we
// do one more step which is to insert an `InstanceData`
// corresponding to this instance. This `InstanceData` can be used
// via `Caller::get_export` if our instance's state "leaks" into
// other instances, even if we don't return successfully from this
// function.
//
// We don't actually load all exports from the instance at this
// time, instead preferring to lazily load them as they're demanded.
// For module/instance exports, though, those aren't actually
// stored in the instance handle so we need to immediately handle
// those here.
let instance = {
let exports = vec![None; compiled_module.module().exports.len()];
let data = InstanceData { id, exports };
Instance::from_wasmtime(data, store)
};
// double-check our guess of what the new instance's ID would be
// was actually correct.
assert_eq!(instance.0, instance_to_be);
// Now that we've recorded all information we need to about this
// instance within a `Store` we can start performing fallible
// initialization. Note that we still defer the `start` function to
// later since that may need to run asynchronously.
//
// If this returns an error (or if the start function traps) then
// any other initialization which may have succeeded which placed
// items from this instance into other instances should be ok when
// those items are loaded and run we'll have all the metadata to
// look at them.
store
.engine()
.allocator()
.initialize(
&mut instance_handle,
compiled_module.module(),
store.engine().config().features.bulk_memory,
)
.map_err(|e| -> Error {
match e {
InstantiationError::Trap(trap) => Trap::from_runtime(trap).into(),
other => other.into(),
}
})?;
Ok((instance, compiled_module.module().start_func))
}
pub(crate) fn from_wasmtime(handle: InstanceData, store: &mut StoreOpaque) -> Instance {
Instance(store.store_data_mut().insert(handle))
}
fn start_raw<T>(&self, store: &mut StoreContextMut<'_, T>, start: FuncIndex) -> Result<()> {
let id = store.0.store_data()[self.0].id;
// If a start function is present, invoke it. Make sure we use all the
// trap-handling configuration in `store` as well.
let instance = store.0.instance_mut(id);
let f = instance.get_exported_func(start);
let vmctx = instance.vmctx_ptr();
unsafe {
super::func::invoke_wasm_and_catch_traps(store, |_default_callee| {
mem::transmute::<
*const VMFunctionBody,
unsafe extern "C" fn(*mut VMContext, *mut VMContext),
>(f.anyfunc.as_ref().func_ptr.as_ptr())(
f.anyfunc.as_ref().vmctx, vmctx
)
})?;
}
Ok(())
}
/// Returns the list of exported items from this [`Instance`].
///
/// # Panics
@@ -319,233 +508,25 @@ impl Instance {
}
}
struct Instantiator<'a> {
imports: ImportSource<'a>,
struct OwnedImports {
functions: PrimaryMap<FuncIndex, VMFunctionImport>,
tables: PrimaryMap<TableIndex, VMTableImport>,
memories: PrimaryMap<MemoryIndex, VMMemoryImport>,
globals: PrimaryMap<GlobalIndex, VMGlobalImport>,
module: &'a Module,
}
enum ImportSource<'a> {
Externs(&'a [Extern]),
Definitions(&'a [Definition]),
}
impl<'a> Instantiator<'a> {
/// Creates a new instantiation context used to process all the initializer
/// directives of a module.
///
/// This doesn't do much work itself beyond setting things up.
///
/// # Unsafety
///
/// This function is unsafe for a few reasons:
///
/// * This assumes that `imports` has already been typechecked and is of the
/// appropriate length. It is memory unsafe if the types of `imports` are
/// not what `module` expects.
///
/// * The `imports` must be safely able to get inserted into `store`. This
/// only applies if `ImportSource::Definitions` is used because this will
/// internally call `Definition::to_extern` which requires that any
/// host functions in the list were created with an original `T` as the
/// store that's being inserted into.
///
/// * The `imports` must all come from the `store` specified.
unsafe fn new(
store: &StoreOpaque,
module: &'a Module,
imports: ImportSource<'a>,
) -> Result<Instantiator<'a>> {
if !Engine::same(store.engine(), module.engine()) {
bail!("cross-`Engine` instantiation is not currently supported");
}
impl OwnedImports {
fn new(module: &Module) -> OwnedImports {
let raw = module.compiled_module().module();
Ok(Instantiator {
imports,
OwnedImports {
functions: PrimaryMap::with_capacity(raw.num_imported_funcs),
tables: PrimaryMap::with_capacity(raw.num_imported_tables),
memories: PrimaryMap::with_capacity(raw.num_imported_memories),
globals: PrimaryMap::with_capacity(raw.num_imported_globals),
module,
})
}
fn run<T>(&mut self, store: &mut StoreContextMut<'_, T>) -> Result<Instance, Error> {
let (instance, start) = self.resolve_imports(store.0)?;
if let Some(start) = start {
Instantiator::start_raw(store, instance, start)?;
}
Ok(instance)
}
/// Resolve all the imports for the module being instantiated, extracting
/// the raw representations and building up the `PrimaryMap` instance for
/// each set of exports.
fn resolve_imports(
&mut self,
store: &mut StoreOpaque,
) -> Result<(Instance, Option<FuncIndex>)> {
store.bump_resource_counts(&self.module)?;
// Read the current module's initializer and move forward the
// initializer pointer as well.
let num_imports = self.module.env_module().initializers.len();
match &self.imports {
ImportSource::Externs(list) => {
assert_eq!(list.len(), num_imports);
for item in list.iter() {
self.push(item.clone(), store);
}
}
ImportSource::Definitions(list) => {
assert_eq!(list.len(), num_imports);
for item in list.iter() {
// This unsafety is encapsulated with
// `Instantiator::new`, documented above.
self.push(unsafe { item.to_extern(store) }, store);
}
}
}
// All initializers have been processed, which means we're ready to
// perform the actual raw instantiation with the raw import values. This
// will register everything except the start function's completion and
// the finished instance will be returned.
self.instantiate_raw(store)
}
fn instantiate_raw(
&mut self,
store: &mut StoreOpaque,
) -> Result<(Instance, Option<FuncIndex>)> {
let compiled_module = self.module.compiled_module();
// Register the module just before instantiation to ensure we keep the module
// properly referenced while in use by the store.
store.modules_mut().register(&self.module);
unsafe {
// The first thing we do is issue an instance allocation request
// to the instance allocator. This, on success, will give us an
// instance handle.
//
// Note that the `host_state` here is a pointer back to the
// `Instance` we'll be returning from this function. This is a
// circular reference so we can't construct it before we construct
// this instance, so we determine what the ID is and then assert
// it's the same later when we do actually insert it.
let instance_to_be = store.store_data().next_id::<InstanceData>();
let mut instance_handle =
store
.engine()
.allocator()
.allocate(InstanceAllocationRequest {
runtime_info: &self.module.runtime_info(),
imports: self.build(),
host_state: Box::new(Instance(instance_to_be)),
store: StorePtr::new(store.traitobj()),
})?;
// The instance still has lots of setup, for example
// data/elements/start/etc. This can all fail, but even on failure
// the instance may persist some state via previous successful
// initialization. For this reason once we have an instance handle
// we immediately insert it into the store to keep it alive.
//
// Note that we `clone` the instance handle just to make easier
// working the the borrow checker here easier. Technically the `&mut
// instance` has somewhat of a borrow on `store` (which
// conflicts with the borrow on `store.engine`) but this doesn't
// matter in practice since initialization isn't even running any
// code here anyway.
let id = store.add_instance(instance_handle.clone(), false);
// Additionally, before we start doing fallible instantiation, we
// do one more step which is to insert an `InstanceData`
// corresponding to this instance. This `InstanceData` can be used
// via `Caller::get_export` if our instance's state "leaks" into
// other instances, even if we don't return successfully from this
// function.
//
// We don't actually load all exports from the instance at this
// time, instead preferring to lazily load them as they're demanded.
// For module/instance exports, though, those aren't actually
// stored in the instance handle so we need to immediately handle
// those here.
let instance = {
let exports = compiled_module
.module()
.exports
.values()
.map(|_index| None)
.collect();
let data = InstanceData { id, exports };
Instance::from_wasmtime(data, store)
};
// double-check our guess of what the new instance's ID would be
// was actually correct.
assert_eq!(instance.0, instance_to_be);
// Now that we've recorded all information we need to about this
// instance within a `Store` we can start performing fallible
// initialization. Note that we still defer the `start` function to
// later since that may need to run asynchronously.
//
// If this returns an error (or if the start function traps) then
// any other initialization which may have succeeded which placed
// items from this instance into other instances should be ok when
// those items are loaded and run we'll have all the metadata to
// look at them.
store
.engine()
.allocator()
.initialize(
&mut instance_handle,
compiled_module.module(),
store.engine().config().features.bulk_memory,
)
.map_err(|e| -> Error {
match e {
InstantiationError::Trap(trap) => Trap::from_runtime(trap).into(),
other => other.into(),
}
})?;
Ok((instance, compiled_module.module().start_func))
}
}
fn start_raw<T>(
store: &mut StoreContextMut<'_, T>,
instance: Instance,
start: FuncIndex,
) -> Result<()> {
let id = store.0.store_data()[instance.0].id;
// If a start function is present, invoke it. Make sure we use all the
// trap-handling configuration in `store` as well.
let instance = store.0.instance_mut(id);
let f = instance.get_exported_func(start);
let vmctx = instance.vmctx_ptr();
unsafe {
super::func::invoke_wasm_and_catch_traps(store, |_default_callee| {
mem::transmute::<
*const VMFunctionBody,
unsafe extern "C" fn(*mut VMContext, *mut VMContext),
>(f.anyfunc.as_ref().func_ptr.as_ptr())(
f.anyfunc.as_ref().vmctx, vmctx
)
})?;
}
Ok(())
}
fn push(&mut self, item: Extern, store: &mut StoreOpaque) {
fn push(&mut self, item: &Extern, store: &mut StoreOpaque) {
match item {
Extern::Func(i) => {
self.functions.push(i.vmimport(store));
@@ -562,7 +543,7 @@ impl<'a> Instantiator<'a> {
}
}
fn build(&self) -> Imports<'_> {
fn as_ref(&self) -> Imports<'_> {
Imports {
tables: self.tables.values().as_slice(),
globals: self.globals.values().as_slice(),
@@ -613,7 +594,15 @@ impl<T> InstancePre<T> {
module: &Module,
items: Vec<Definition>,
) -> Result<InstancePre<T>> {
typecheck_defs(store, module, &items)?;
for import in items.iter() {
if !import.comes_from_same_store(store) {
bail!("cross-`Store` instantiation is not currently supported");
}
}
typecheck(store, module, &items, |cx, ty, item| {
cx.definition(ty, item)
})?;
let host_funcs = items
.iter()
.filter(|i| match i {
@@ -645,20 +634,14 @@ impl<T> InstancePre<T> {
/// function will panic if the `store` provided comes from a different
/// [`Engine`] than the [`InstancePre`] originally came from.
pub fn instantiate(&self, mut store: impl AsContextMut<Data = T>) -> Result<Instance> {
// For the unsafety here the typecheck happened at creation time of this
// structure and then othrewise the `T` of `InstancePre<T>` connects any
// host functions we have in our definition list to the `store` that was
// passed in.
let mut store = store.as_context_mut();
let mut instantiator = unsafe {
self.verify_store_and_reserve_space(&mut store.0)?;
Instantiator::new(
store.0,
&self.module,
ImportSource::Definitions(&self.items),
)?
};
instantiator.run(&mut store)
let imports =
pre_instantiate_raw(&mut store.0, &self.module, &self.items, self.host_funcs)?;
// This unsafety should be handled by the type-checking performed by the
// constructor of `InstancePre` to assert that all the imports we're passing
// in match the module we're instantiating.
unsafe { Instance::new_started(&mut store, &self.module, imports.as_ref()) }
}
/// Creates a new instance, running the start function asynchronously
@@ -680,60 +663,48 @@ impl<T> InstancePre<T> {
where
T: Send,
{
// For the unsafety here see above
let mut store = store.as_context_mut();
let mut i = unsafe {
self.verify_store_and_reserve_space(&mut store.0)?;
Instantiator::new(
store.0,
&self.module,
ImportSource::Definitions(&self.items),
)?
};
let imports =
pre_instantiate_raw(&mut store.0, &self.module, &self.items, self.host_funcs)?;
let mut store = store.as_context_mut();
assert!(
store.0.async_support(),
"cannot use `new_async` without enabling async support on the config"
);
store
.on_fiber(|store| i.run(&mut store.as_context_mut()))
.await?
// This unsafety should be handled by the type-checking performed by the
// constructor of `InstancePre` to assert that all the imports we're passing
// in match the module we're instantiating.
unsafe { Instance::new_started_async(&mut store, &self.module, imports.as_ref()).await }
}
}
fn verify_store_and_reserve_space(&self, store: &mut StoreOpaque) -> Result<()> {
for import in self.items.iter() {
if !import.comes_from_same_store(store) {
bail!("cross-`Store` instantiation is not currently supported");
}
}
/// Helper function shared between
/// `InstancePre::{instantiate,instantiate_async}`
///
/// This is an out-of-line function to avoid the generic on `InstancePre` and
/// get this compiled into the `wasmtime` crate to avoid having it monomorphized
/// elsewhere.
fn pre_instantiate_raw(
store: &mut StoreOpaque,
module: &Module,
items: &[Definition],
host_funcs: usize,
) -> Result<OwnedImports> {
// Any linker-defined function of the `Definition::HostFunc` variant
// will insert a function into the store automatically as part of
// instantiation, so reserve space here to make insertion more efficient
// as it won't have to realloc during the instantiation.
store.store_data_mut().reserve_funcs(self.host_funcs);
Ok(())
}
}
store.store_data_mut().reserve_funcs(host_funcs);
fn typecheck_externs(store: &mut StoreOpaque, module: &Module, imports: &[Extern]) -> Result<()> {
for import in imports {
let mut imports = OwnedImports::new(module);
for import in items {
if !import.comes_from_same_store(store) {
bail!("cross-`Store` instantiation is not currently supported");
}
}
typecheck(store, module, imports, |cx, ty, item| cx.extern_(ty, item))
// This unsafety should be encapsulated in the constructor of
// `InstancePre` where the `T` of the original item should match the
// `T` of the store.
let item = unsafe { import.to_extern(store) };
imports.push(&item, store);
}
fn typecheck_defs(store: &mut StoreOpaque, module: &Module, imports: &[Definition]) -> Result<()> {
for import in imports {
if !import.comes_from_same_store(store) {
bail!("cross-`Store` instantiation is not currently supported");
}
}
typecheck(store, module, imports, |cx, ty, item| {
cx.definition(ty, item)
})
Ok(imports)
}
fn typecheck<I>(

6
tests/all/call_hook.rs
View File

@@ -614,7 +614,7 @@ async fn basic_async_hook() -> Result<(), Error> {
"#;
let module = Module::new(&engine, wat)?;
let inst = linker.instantiate(&mut store, &module)?;
let inst = linker.instantiate_async(&mut store, &module).await?;
let export = inst
.get_export(&mut store, "export")
.expect("get export")
@@ -694,7 +694,7 @@ async fn timeout_async_hook() -> Result<(), Error> {
"#;
let module = Module::new(&engine, wat)?;
let inst = linker.instantiate(&mut store, &module)?;
let inst = linker.instantiate_async(&mut store, &module).await?;
let export = inst
.get_typed_func::<(), (), _>(&mut store, "export")
.expect("export is func");
@@ -764,7 +764,7 @@ async fn drop_suspended_async_hook() -> Result<(), Error> {
"#;
let module = Module::new(&engine, wat)?;
let inst = linker.instantiate(&mut store, &module)?;
let inst = linker.instantiate_async(&mut store, &module).await?;
assert_eq!(*store.data(), 0);
let export = inst
.get_typed_func::<(), (), _>(&mut store, "")

17
tests/all/epoch_interruption.rs
View File

@@ -69,9 +69,6 @@ fn run_and_count_yields_or_trap<F: Fn(Arc<Engine>)>(
let linker = make_env(&engine);
let module = Module::new(&engine, wasm).unwrap();
let mut store = Store::new(&engine, ());
let instance = linker.instantiate(&mut store, &module).unwrap();
let f = instance.get_func(&mut store, "run").unwrap();
store.set_epoch_deadline(initial);
match delta {
Some(delta) => {
@@ -85,7 +82,11 @@ fn run_and_count_yields_or_trap<F: Fn(Arc<Engine>)>(
let engine_clone = engine.clone();
setup_func(engine_clone);
let mut future = Box::pin(f.call_async(&mut store, &[], &mut []));
let mut future = Box::pin(async {
let instance = linker.instantiate_async(&mut store, &module).await.unwrap();
let f = instance.get_func(&mut store, "run").unwrap();
f.call_async(&mut store, &[], &mut []).await
});
let mut yields = 0;
loop {
match future
@@ -394,13 +395,15 @@ fn drop_future_on_epoch_yield() {
let module = Module::new(&engine, wasm).unwrap();
let mut store = Store::new(&engine, ());
let instance = linker.instantiate(&mut store, &module).unwrap();
let f = instance.get_func(&mut store, "run").unwrap();
store.set_epoch_deadline(1);
store.epoch_deadline_async_yield_and_update(1);
let mut future = Box::pin(f.call_async(&mut store, &[], &mut []));
let mut future = Box::pin(async {
let instance = linker.instantiate_async(&mut store, &module).await.unwrap();
let f = instance.get_func(&mut store, "run").unwrap();
f.call_async(&mut store, &[], &mut []).await
});
match future
.as_mut()
.poll(&mut Context::from_waker(&dummy_waker()))