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use crate::component::func::{bad_type_info, desc, LiftContext, LowerContext};
use crate::component::matching::InstanceType;
use crate::component::{ComponentType, Lift, Lower};
use crate::prelude::*;
use crate::runtime::vm::component::{ComponentInstance, InstanceFlags, ResourceTables};
use crate::runtime::vm::{SendSyncPtr, VMFuncRef, ValRaw};
use crate::store::{StoreId, StoreOpaque};
use crate::{AsContextMut, StoreContextMut, Trap};
use core::any::TypeId;
use core::fmt;
use core::marker;
use core::mem::MaybeUninit;
use core::ptr::NonNull;
use core::sync::atomic::{AtomicU64, Ordering::Relaxed};
use wasmtime_environ::component::{
CanonicalAbiInfo, ComponentTypes, DefinedResourceIndex, InterfaceType, ResourceIndex,
TypeResourceTableIndex,
};
/// Representation of a resource type in the component model.
///
/// Resources are currently always represented as 32-bit integers but they have
/// unique types across instantiations and the host. For example instantiating
/// the same component twice means that defined resource types in the component
/// will all be different. Values of this type can be compared to see if
/// resources have the same type.
///
/// Resource types can also be defined on the host in addition to guests. On the
/// host resource types are tied to a `T`, an arbitrary Rust type. Two host
/// resource types are the same if they point to the same `T`.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub struct ResourceType {
kind: ResourceTypeKind,
}
impl ResourceType {
/// Creates a new host resource type corresponding to `T`.
///
/// Note that `T` is a mostly a phantom type parameter here. It does not
/// need to reflect the actual storage of the resource `T`. For example this
/// is valid:
///
/// ```rust
/// use wasmtime::component::ResourceType;
///
/// struct Foo;
///
/// let ty = ResourceType::host::<Foo>();
/// ```
///
/// A resource type of type `ResourceType::host::<T>()` will match the type
/// of the value produced by `Resource::<T>::new_{own,borrow}`.
pub fn host<T: 'static>() -> ResourceType {
ResourceType {
kind: ResourceTypeKind::Host(TypeId::of::<T>()),
}
}
pub(crate) fn guest(
store: StoreId,
instance: &ComponentInstance,
id: DefinedResourceIndex,
) -> ResourceType {
ResourceType {
kind: ResourceTypeKind::Guest {
store,
instance: instance as *const _ as usize,
id,
},
}
}
pub(crate) fn uninstantiated(types: &ComponentTypes, index: ResourceIndex) -> ResourceType {
ResourceType {
kind: ResourceTypeKind::Uninstantiated {
component: types as *const _ as usize,
index,
},
}
}
}
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
enum ResourceTypeKind {
Host(TypeId),
Guest {
store: StoreId,
// For now this is the `*mut ComponentInstance` pointer within the store
// that this guest corresponds to. It's used to distinguish different
// instantiations of the same component within the store.
instance: usize,
id: DefinedResourceIndex,
},
Uninstantiated {
// Like `instance` in `Guest` above this is a pointer and is used to
// distinguish between two components. Technically susceptible to ABA
// issues but the consequence is a nonexistent resource would be equal
// to a new resource so there's not really any issue with that.
component: usize,
index: ResourceIndex,
},
}
/// A host-defined resource in the component model.
///
/// This type can be thought of as roughly a newtype wrapper around `u32` for
/// use as a resource with the component model. The main guarantee that the
/// component model provides is that the `u32` is not forgeable by guests and
/// there are guaranteed semantics about when a `u32` may be in use by the guest
/// and when it's guaranteed no longer needed. This means that it is safe for
/// embedders to consider the internal `u32` representation "trusted" and use it
/// for things like table indices with infallible accessors that panic on
/// out-of-bounds. This should only panic for embedder bugs, not because of any
/// possible behavior in the guest.
///
/// A `Resource<T>` value dynamically represents both an `(own $t)` in the
/// component model as well as a `(borrow $t)`. It can be inspected via
/// [`Resource::owned`] to test whether it is an owned handle. An owned handle
/// which is not actively borrowed can be destroyed at any time as it's
/// guaranteed that the guest does not have access to it. A borrowed handle, on
/// the other hand, may be accessed by the guest so it's not necessarily
/// guaranteed to be able to be destroyed.
///
/// Note that the "own" and "borrow" here refer to the component model, not
/// Rust. The semantics of Rust ownership and borrowing are slightly different
/// than the component model's (but spiritually the same) in that more dynamic
/// tracking is employed as part of the component model. This means that it's
/// possible to get runtime errors when using a `Resource<T>`. For example it is
/// an error to call [`Resource::new_borrow`] and pass that to a component
/// function expecting `(own $t)` and this is not statically disallowed.
///
/// The [`Resource`] type implements both the [`Lift`] and [`Lower`] trait to be
/// used with typed functions in the component model or as part of aggregate
/// structures and datatypes.
///
/// # Destruction of a resource
///
/// Resources in the component model are optionally defined with a destructor,
/// but this host resource type does not specify a destructor. It is left up to
/// the embedder to be able to determine how best to a destroy a resource when
/// it is owned.
///
/// Note, though, that while [`Resource`] itself does not specify destructors
/// it's still possible to do so via the [`Linker::resource`] definition. When a
/// resource type is defined for a guest component a destructor can be specified
/// which can be used to hook into resource destruction triggered by the guest.
///
/// This means that there are two ways that resource destruction is handled:
///
/// * Host resources destroyed by the guest can hook into the
/// [`Linker::resource`] destructor closure to handle resource destruction.
/// This could, for example, remove table entries.
///
/// * Host resources owned by the host itself have no automatic means of
/// destruction. The host can make its own determination that its own resource
/// is not lent out to the guest and at that time choose to destroy or
/// deallocate it.
///
/// # Dynamic behavior of a resource
///
/// A host-defined [`Resource`] does not necessarily represent a static value.
/// Its internals may change throughout its usage to track the state associated
/// with the resource. The internal 32-bit host-defined representation never
/// changes, however.
///
/// For example if there's a component model function of the form:
///
/// ```wasm
/// (func (param "a" (borrow $t)) (param "b" (own $t)))
/// ```
///
/// Then that can be extracted in Rust with:
///
/// ```rust,ignore
/// let func = instance.get_typed_func::<(&Resource<T>, &Resource<T>), ()>(&mut store, "name")?;
/// ```
///
/// Here the exact same resource can be provided as both arguments but that is
/// not valid to do so because the same resource cannot be actively borrowed and
/// passed by-value as the second parameter at the same time. The internal state
/// in `Resource<T>` will track this information and provide a dynamic runtime
/// error in this situation.
///
/// Mostly it's important to be aware that there is dynamic state associated
/// with a [`Resource<T>`] to provide errors in situations that cannot be
/// statically ruled out.
///
/// # Borrows and host responsibilities
///
/// Borrows to resources in the component model are guaranteed to be transient
/// such that if a borrow is passed as part of a function call then when the
/// function returns it's guaranteed that the guest no longer has access to the
/// resource. This guarantee, however, must be manually upheld by the host when
/// it receives its own borrow.
///
/// As mentioned above the [`Resource<T>`] type can represent a borrowed value
/// in addition to an owned value. This means a guest can provide the host with
/// a borrow, such as an argument to an imported function:
///
/// ```rust,ignore
/// linker.root().func_wrap("name", |_cx, (r,): (Resource<MyType>,)| {
/// assert!(!r.owned());
/// // .. here `r` is a borrowed value provided by the guest and the host
/// // shouldn't continue to access it beyond the scope of this call
/// })?;
/// ```
///
/// In this situation the host should take care to not attempt to persist the
/// resource beyond the scope of the call. It's the host's resource so it
/// technically can do what it wants with it but nothing is statically
/// preventing `r` to stay pinned to the lifetime of the closure invocation.
/// It's considered a mistake that the host performed if `r` is persisted too
/// long and accessed at the wrong time.
///
/// [`Linker::resource`]: crate::component::LinkerInstance::resource
pub struct Resource<T> {
/// The host-defined 32-bit representation of this resource.
rep: u32,
/// Dear rust please consider `T` used even though it's not actually used.
_marker: marker::PhantomData<fn() -> T>,
state: AtomicResourceState,
}
/// Internal dynamic state tracking for this resource. This can be one of
/// four different states:
///
/// * `BORROW` / `u64::MAX` - this indicates that this is a borrowed
/// resource. The `rep` doesn't live in the host table and this `Resource`
/// instance is transiently available. It's the host's responsibility to
/// discard this resource when the borrow duration has finished.
///
/// * `NOT_IN_TABLE` / `u64::MAX - 1` - this indicates that this is an owned
/// resource not present in any store's table. This resource is not lent
/// out. It can be passed as an `(own $t)` directly into a guest's table
/// or it can be passed as a borrow to a guest which will insert it into
/// a host store's table for dynamic borrow tracking.
///
/// * `TAKEN` / `u64::MAX - 2` - while the `rep` is available the resource
/// has been dynamically moved into a guest and cannot be moved in again.
/// This is used for example to prevent the same resource from being
/// passed twice to a guest.
///
/// * All other values - any other value indicates that the value is an
/// index into a store's table of host resources. It's guaranteed that the
/// table entry represents a host resource and the resource may have
/// borrow tracking associated with it. The low 32-bits of the value are
/// the table index and the upper 32-bits are the generation.
///
/// Note that this is an `AtomicU64` but it's not intended to actually be
/// used in conjunction with threads as generally a `Store<T>` lives on one
/// thread at a time. The `AtomicU64` here is used to ensure that this type
/// is `Send + Sync` when captured as a reference to make async programming
/// more ergonomic.
struct AtomicResourceState(AtomicU64);
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
enum ResourceState {
Borrow,
NotInTable,
Taken,
Index(HostResourceIndex),
}
impl AtomicResourceState {
const BORROW: Self = Self(AtomicU64::new(ResourceState::BORROW));
const NOT_IN_TABLE: Self = Self(AtomicU64::new(ResourceState::NOT_IN_TABLE));
fn get(&self) -> ResourceState {
ResourceState::decode(self.0.load(Relaxed))
}
fn swap(&self, state: ResourceState) -> ResourceState {
ResourceState::decode(self.0.swap(state.encode(), Relaxed))
}
}
impl ResourceState {
// See comments on `state` above for info about these values.
const BORROW: u64 = u64::MAX;
const NOT_IN_TABLE: u64 = u64::MAX - 1;
const TAKEN: u64 = u64::MAX - 2;
fn decode(bits: u64) -> ResourceState {
match bits {
Self::BORROW => Self::Borrow,
Self::NOT_IN_TABLE => Self::NotInTable,
Self::TAKEN => Self::Taken,
other => Self::Index(HostResourceIndex(other)),
}
}
fn encode(&self) -> u64 {
match self {
Self::Borrow => Self::BORROW,
Self::NotInTable => Self::NOT_IN_TABLE,
Self::Taken => Self::TAKEN,
Self::Index(index) => index.0,
}
}
}
/// Metadata tracking the state of resources within a `Store`.
///
/// This is a borrowed structure created from a `Store` piecemeal from below.
/// The `ResourceTables` type holds most of the raw information and this
/// structure tacks on a reference to `HostResourceData` to track generation
/// numbers of host indices.
pub struct HostResourceTables<'a> {
tables: ResourceTables<'a>,
host_resource_data: &'a mut HostResourceData,
}
/// Metadata for host-owned resources owned within a `Store`.
///
/// This metadata is used to prevent the ABA problem with indices handed out as
/// part of `Resource` and `ResourceAny`. Those structures are `Copy` meaning
/// that it's easy to reuse them, possibly accidentally. To prevent issues in
/// the host Wasmtime attaches both an index (within `ResourceTables`) as well
/// as a 32-bit generation counter onto each `HostResourceIndex` which the host
/// actually holds in `Resource` and `ResourceAny`.
///
/// This structure holds a list which is a parallel list to the "list of reps"
/// that's stored within `ResourceTables` elsewhere in the `Store`. This
/// parallel list holds the last known generation of each element in the table.
/// The generation is then compared on access to make sure it's the same.
///
/// Whenever a slot in the table is allocated the `cur_generation` field is
/// pushed at the corresponding index of `generation_of_table_slot`. Whenever
/// a field is accessed the current value of `generation_of_table_slot` is
/// checked against the generation of the index. Whenever a slot is deallocated
/// the generation is incremented. Put together this means that any access of a
/// deallocated slot should deterministically provide an error.
#[derive(Default)]
pub struct HostResourceData {
cur_generation: u32,
table_slot_metadata: Vec<TableSlot>,
}
#[derive(Copy, Clone)]
struct TableSlot {
generation: u32,
flags: Option<InstanceFlags>,
dtor: Option<SendSyncPtr<VMFuncRef>>,
}
/// Host representation of an index into a table slot.
///
/// This is morally (u32, u32) but is encoded as a 64-bit integer. The low
/// 32-bits are the table index and the upper 32-bits are the generation
/// counter.
#[derive(PartialEq, Eq, Debug, Copy, Clone)]
#[repr(transparent)]
pub struct HostResourceIndex(u64);
impl HostResourceIndex {
fn new(idx: u32, gen: u32) -> HostResourceIndex {
HostResourceIndex(u64::from(idx) | (u64::from(gen) << 32))
}
fn index(&self) -> u32 {
u32::try_from(self.0 & 0xffffffff).unwrap()
}
fn gen(&self) -> u32 {
u32::try_from(self.0 >> 32).unwrap()
}
}
impl<'a> HostResourceTables<'a> {
pub fn new_host(store: &'a mut StoreOpaque) -> HostResourceTables<'a> {
let (calls, host_table, host_resource_data) = store.component_resource_state();
HostResourceTables::from_parts(
ResourceTables {
host_table: Some(host_table),
calls,
tables: None,
},
host_resource_data,
)
}
pub fn from_parts(
tables: ResourceTables<'a>,
host_resource_data: &'a mut HostResourceData,
) -> Self {
HostResourceTables {
tables,
host_resource_data,
}
}
/// Lifts an `own` resource that resides in the host's tables at the `idx`
/// specified into its `rep`.
///
/// # Errors
///
/// Returns an error if `idx` doesn't point to a valid owned resource, or
/// if `idx` can't be lifted as an `own` (e.g. it has active borrows).
pub fn host_resource_lift_own(&mut self, idx: HostResourceIndex) -> Result<u32> {
let (idx, _) = self.validate_host_index(idx, true)?;
self.tables.resource_lift_own(None, idx)
}
/// See [`HostResourceTables::host_resource_lift_own`].
pub fn host_resource_lift_borrow(&mut self, idx: HostResourceIndex) -> Result<u32> {
let (idx, _) = self.validate_host_index(idx, false)?;
self.tables.resource_lift_borrow(None, idx)
}
/// Lowers an `own` resource to be owned by the host.
///
/// This returns a new index into the host's set of resource tables which
/// will point to the `rep` specified. The returned index is suitable for
/// conversion into either [`Resource`] or [`ResourceAny`].
///
/// The `dtor` and instance `flags` are specified as well to know what
/// destructor to run when this resource is destroyed.
pub fn host_resource_lower_own(
&mut self,
rep: u32,
dtor: Option<NonNull<VMFuncRef>>,
flags: Option<InstanceFlags>,
) -> Result<HostResourceIndex> {
let idx = self.tables.resource_lower_own(None, rep)?;
Ok(self.new_host_index(idx, dtor, flags))
}
/// See [`HostResourceTables::host_resource_lower_own`].
pub fn host_resource_lower_borrow(&mut self, rep: u32) -> Result<HostResourceIndex> {
let idx = self.tables.resource_lower_borrow(None, rep)?;
Ok(self.new_host_index(idx, None, None))
}
/// Validates that `idx` is still valid for the host tables, notably
/// ensuring that the generation listed in `idx` is the same as the
/// last recorded generation of the slot itself.
///
/// The `is_removal` option indicates whether or not this table access will
/// end up removing the element from the host table. In such a situation the
/// current generation number is incremented.
fn validate_host_index(
&mut self,
idx: HostResourceIndex,
is_removal: bool,
) -> Result<(u32, Option<TableSlot>)> {
let actual = usize::try_from(idx.index())
.ok()
.and_then(|i| self.host_resource_data.table_slot_metadata.get(i).copied());
// If `idx` is out-of-bounds then skip returning an error. In such a
// situation the operation that this is guarding will return a more
// precise error, such as a lift operation.
if let Some(actual) = actual {
if actual.generation != idx.gen() {
bail!("host-owned resource is being used with the wrong type");
}
}
// Bump the current generation of this is a removal to ensure any
// future item placed in this slot can't be pointed to by the `idx`
// provided above.
if is_removal {
self.host_resource_data.cur_generation += 1;
}
Ok((idx.index(), actual))
}
/// Creates a new `HostResourceIndex` which will point to the raw table
/// slot provided by `idx`.
///
/// This will register metadata necessary to track the current generation
/// in the returned `HostResourceIndex` as well.
fn new_host_index(
&mut self,
idx: u32,
dtor: Option<NonNull<VMFuncRef>>,
flags: Option<InstanceFlags>,
) -> HostResourceIndex {
let list = &mut self.host_resource_data.table_slot_metadata;
let info = TableSlot {
generation: self.host_resource_data.cur_generation,
flags,
dtor: dtor.map(SendSyncPtr::new),
};
match list.get_mut(idx as usize) {
Some(slot) => *slot = info,
None => {
// Resource handles start at 1, not zero, so push two elements
// for the first resource handle.
if list.is_empty() {
assert_eq!(idx, 1);
list.push(TableSlot {
generation: 0,
flags: None,
dtor: None,
});
}
assert_eq!(idx as usize, list.len());
list.push(info);
}
}
HostResourceIndex::new(idx, info.generation)
}
/// Drops a host-owned resource from host tables.
///
/// This method will attempt to interpret `idx` as pointing to either a
/// `borrow` or `own` resource with the `expected` type specified. This
/// method will then return the underlying `rep` if it points to an `own`
/// resource which can then be further processed for destruction.
///
/// # Errors
///
/// Returns an error if `idx` doesn't point to a valid resource, points to
/// an `own` with active borrows, or if it doesn't have the type `expected`
/// in the host tables.
fn host_resource_drop(&mut self, idx: HostResourceIndex) -> Result<Option<(u32, TableSlot)>> {
let (idx, slot) = self.validate_host_index(idx, true)?;
match self.tables.resource_drop(None, idx)? {
Some(rep) => Ok(Some((rep, slot.unwrap()))),
None => Ok(None),
}
}
/// Lowers an `own` resource into the guest, converting the `rep` specified
/// into a guest-local index.
///
/// The `ty` provided is which table to put this into.
pub fn guest_resource_lower_own(
&mut self,
rep: u32,
ty: TypeResourceTableIndex,
) -> Result<u32> {
self.tables.resource_lower_own(Some(ty), rep)
}
/// Lowers a `borrow` resource into the guest, converting the `rep`
/// specified into a guest-local index.
///
/// The `ty` provided is which table to put this into.
///
/// Note that this cannot be used in isolation because lowering a borrow
/// into a guest has a special case where `rep` is returned directly if `ty`
/// belongs to the component being lowered into. That property must be
/// handled by the caller of this function.
pub fn guest_resource_lower_borrow(
&mut self,
rep: u32,
ty: TypeResourceTableIndex,
) -> Result<u32> {
self.tables.resource_lower_borrow(Some(ty), rep)
}
/// Lifts an `own` resource from the `idx` specified from the table `ty`.
///
/// This will lookup the appropriate table in the guest and return the `rep`
/// corresponding to `idx` if it's valid.
pub fn guest_resource_lift_own(&mut self, idx: u32, ty: TypeResourceTableIndex) -> Result<u32> {
self.tables.resource_lift_own(Some(ty), idx)
}
/// Lifts a `borrow` resource from the `idx` specified from the table `ty`.
///
/// This will lookup the appropriate table in the guest and return the `rep`
/// corresponding to `idx` if it's valid.
pub fn guest_resource_lift_borrow(
&mut self,
idx: u32,
ty: TypeResourceTableIndex,
) -> Result<u32> {
self.tables.resource_lift_borrow(Some(ty), idx)
}
/// Begins a call into the component instance, starting recording of
/// metadata related to resource borrowing.
#[inline]
pub fn enter_call(&mut self) {
self.tables.enter_call()
}
/// Completes a call into the component instance, validating that it's ok to
/// complete by ensuring the are no remaining active borrows.
#[inline]
pub fn exit_call(&mut self) -> Result<()> {
self.tables.exit_call()
}
}
impl<T> Resource<T>
where
T: 'static,
{
/// Creates a new owned resource with the `rep` specified.
///
/// The returned value is suitable for passing to a guest as either a
/// `(borrow $t)` or `(own $t)`.
pub fn new_own(rep: u32) -> Resource<T> {
Resource {
state: AtomicResourceState::NOT_IN_TABLE,
rep,
_marker: marker::PhantomData,
}
}
/// Creates a new borrowed resource which isn't actually rooted in any
/// ownership.
///
/// This can be used to pass to a guest as a borrowed resource and the
/// embedder will know that the `rep` won't be in use by the guest
/// afterwards. Exactly how the lifetime of `rep` works is up to the
/// embedder.
pub fn new_borrow(rep: u32) -> Resource<T> {
Resource {
state: AtomicResourceState::BORROW,
rep,
_marker: marker::PhantomData,
}
}
/// Returns the underlying 32-bit representation used to originally create
/// this resource.
pub fn rep(&self) -> u32 {
self.rep
}
/// Returns whether this is an owned resource or not.
///
/// Owned resources can be safely destroyed by the embedder at any time, and
/// borrowed resources have an owner somewhere else on the stack so can only
/// be accessed, not destroyed.
pub fn owned(&self) -> bool {
match self.state.get() {
ResourceState::Borrow => false,
ResourceState::Taken | ResourceState::NotInTable | ResourceState::Index(_) => true,
}
}
fn lower_to_index<U>(&self, cx: &mut LowerContext<'_, U>, ty: InterfaceType) -> Result<u32> {
match ty {
InterfaceType::Own(t) => {
let rep = match self.state.get() {
// If this is a borrow resource then this is a dynamic
// error on behalf of the embedder.
ResourceState::Borrow => {
bail!("cannot lower a `borrow` resource into an `own`")
}
// If this resource does not yet live in a table then we're
// dynamically transferring ownership to wasm. Record that
// it's no longer present and then pass through the
// representation.
ResourceState::NotInTable => {
let prev = self.state.swap(ResourceState::Taken);
assert_eq!(prev, ResourceState::NotInTable);
self.rep
}
// This resource has already been moved into wasm so this is
// a dynamic error on behalf of the embedder.
ResourceState::Taken => bail!("host resource already consumed"),
// If this resource lives in a host table then try to take
// it out of the table, which may fail, and on success we
// can move the rep into the guest table.
ResourceState::Index(idx) => cx.host_resource_lift_own(idx)?,
};
cx.guest_resource_lower_own(t, rep)
}
InterfaceType::Borrow(t) => {
let rep = match self.state.get() {
// If this is already a borrowed resource, nothing else to
// do and the rep is passed through.
ResourceState::Borrow => self.rep,
// If this resource is already gone, that's a dynamic error
// for the embedder.
ResourceState::Taken => bail!("host resource already consumed"),
// If this resource is not currently in a table then it
// needs to move into a table to participate in state
// related to borrow tracking. Execute the
// `host_resource_lower_own` operation here and update our
// state.
//
// Afterwards this is the same as the `idx` case below.
//
// Note that flags/dtor are passed as `None` here since
// `Resource<T>` doesn't offer destruction support.
ResourceState::NotInTable => {
let idx = cx.host_resource_lower_own(self.rep, None, None)?;
let prev = self.state.swap(ResourceState::Index(idx));
assert_eq!(prev, ResourceState::NotInTable);
cx.host_resource_lift_borrow(idx)?
}
// If this resource lives in a table then it needs to come
// out of the table with borrow-tracking employed.
ResourceState::Index(idx) => cx.host_resource_lift_borrow(idx)?,
};
cx.guest_resource_lower_borrow(t, rep)
}
_ => bad_type_info(),
}
}
fn lift_from_index(cx: &mut LiftContext<'_>, ty: InterfaceType, index: u32) -> Result<Self> {
let (state, rep) = match ty {
// Ownership is being transferred from a guest to the host, so move
// it from the guest table into a new `Resource`. Note that this
// isn't immediately inserted into the host table and that's left
// for the future if it's necessary to take a borrow from this owned
// resource.
InterfaceType::Own(t) => {
debug_assert!(cx.resource_type(t) == ResourceType::host::<T>());
let (rep, dtor, flags) = cx.guest_resource_lift_own(t, index)?;
assert!(dtor.is_some());
assert!(flags.is_none());
(AtomicResourceState::NOT_IN_TABLE, rep)
}
// The borrow here is lifted from the guest, but note the lack of
// `host_resource_lower_borrow` as it's intentional. Lowering
// a borrow has a special case in the canonical ABI where if the
// receiving module is the owner of the resource then it directly
// receives the `rep` and no other dynamic tracking is employed.
// This effectively mirrors that even though the canonical ABI
// isn't really all that applicable in host context here.
InterfaceType::Borrow(t) => {
debug_assert!(cx.resource_type(t) == ResourceType::host::<T>());
let rep = cx.guest_resource_lift_borrow(t, index)?;
(AtomicResourceState::BORROW, rep)
}
_ => bad_type_info(),
};
Ok(Resource {
state,
rep,
_marker: marker::PhantomData,
})
}
/// Attempts to convert a [`ResourceAny`] into [`Resource`].
///
/// This method will check that `resource` has type
/// `ResourceType::host::<T>()` and then convert it into a typed version of
/// the resource.
///
/// # Errors
///
/// This function will return an error if `resource` does not have type
/// `ResourceType::host::<T>()`. This function may also return an error if
/// `resource` is no longer valid, for example it was previously converted.
///
/// # Panics
///
/// This function will panic if `resource` does not belong to the `store`
/// specified.
pub fn try_from_resource_any(
resource: ResourceAny,
mut store: impl AsContextMut,
) -> Result<Self> {
let store = store.as_context_mut();
let mut tables = HostResourceTables::new_host(store.0);
let ResourceAny { idx, ty, owned } = resource;
ensure!(ty == ResourceType::host::<T>(), "resource type mismatch");
let (state, rep) = if owned {
let rep = tables.host_resource_lift_own(idx)?;
(AtomicResourceState::NOT_IN_TABLE, rep)
} else {
// For borrowed handles, first acquire the `rep` via lifting the
// borrow. Afterwards though remove any dynamic state associated
// with this borrow. `Resource<T>` doesn't participate in dynamic
// state tracking and it's assumed embedders know what they're
// doing, so the drop call will clear out that a borrow is active
//
// Note that the result of `drop` should always be `None` as it's a
// borrowed handle, so assert so.
let rep = tables.host_resource_lift_borrow(idx)?;
let res = tables.host_resource_drop(idx)?;
assert!(res.is_none());
(AtomicResourceState::BORROW, rep)
};
Ok(Resource {
state,
rep,
_marker: marker::PhantomData,
})
}
/// See [`ResourceAny::try_from_resource`]
pub fn try_into_resource_any(self, store: impl AsContextMut) -> Result<ResourceAny> {
ResourceAny::try_from_resource(self, store)
}
}
unsafe impl<T: 'static> ComponentType for Resource<T> {
const ABI: CanonicalAbiInfo = CanonicalAbiInfo::SCALAR4;
type Lower = <u32 as ComponentType>::Lower;
fn typecheck(ty: &InterfaceType, types: &InstanceType<'_>) -> Result<()> {
let resource = match ty {
InterfaceType::Own(t) | InterfaceType::Borrow(t) => *t,
other => bail!("expected `own` or `borrow`, found `{}`", desc(other)),
};
match types.resource_type(resource).kind {
ResourceTypeKind::Host(id) if TypeId::of::<T>() == id => {}
_ => bail!("resource type mismatch"),
}
Ok(())
}
}
unsafe impl<T: 'static> Lower for Resource<T> {
fn lower<U>(
&self,
cx: &mut LowerContext<'_, U>,
ty: InterfaceType,
dst: &mut MaybeUninit<Self::Lower>,
) -> Result<()> {
self.lower_to_index(cx, ty)?
.lower(cx, InterfaceType::U32, dst)
}
fn store<U>(
&self,
cx: &mut LowerContext<'_, U>,
ty: InterfaceType,
offset: usize,
) -> Result<()> {
self.lower_to_index(cx, ty)?
.store(cx, InterfaceType::U32, offset)
}
}
unsafe impl<T: 'static> Lift for Resource<T> {
fn lift(cx: &mut LiftContext<'_>, ty: InterfaceType, src: &Self::Lower) -> Result<Self> {
let index = u32::lift(cx, InterfaceType::U32, src)?;
Resource::lift_from_index(cx, ty, index)
}
fn load(cx: &mut LiftContext<'_>, ty: InterfaceType, bytes: &[u8]) -> Result<Self> {
let index = u32::load(cx, InterfaceType::U32, bytes)?;
Resource::lift_from_index(cx, ty, index)
}
}
impl<T> fmt::Debug for Resource<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let state = match self.state.get() {
ResourceState::Borrow => "borrow",
ResourceState::NotInTable => "own (not in table)",
ResourceState::Taken => "taken",
ResourceState::Index(_) => "own",
};
f.debug_struct("Resource")
.field("rep", &self.rep)
.field("state", &state)
.finish()
}
}
/// Representation of a resource in the component model, either a guest-defined
/// or a host-defined resource.
///
/// This type is similar to [`Resource`] except that it can be used to represent
/// any resource, either host or guest. This type cannot be directly constructed
/// and is only available if the guest returns it to the host (e.g. a function
/// returning a guest-defined resource) or by a conversion from [`Resource`] via
/// [`ResourceAny::try_from_resource`].
/// This type also does not carry a static type parameter `T` for example and
/// does not have as much information about its type.
/// This means that it's possible to get runtime type-errors when
/// using this type because it cannot statically prevent mismatching resource
/// types.
///
/// Like [`Resource`] this type represents either an `own` or a `borrow`
/// resource internally. Unlike [`Resource`], however, a [`ResourceAny`] must
/// always be explicitly destroyed with the [`ResourceAny::resource_drop`]
/// method. This will update internal dynamic state tracking and invoke the
/// WebAssembly-defined destructor for a resource, if any.
///
/// Note that it is required to call `resource_drop` for all instances of
/// [`ResourceAny`]: even borrows. Both borrows and own handles have state
/// associated with them that must be discarded by the time they're done being
/// used.
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub struct ResourceAny {
idx: HostResourceIndex,
ty: ResourceType,
owned: bool,
}
impl ResourceAny {
/// Attempts to convert an imported [`Resource`] into [`ResourceAny`].
///
/// * `resource` is the resource to convert.
/// * `store` is the store to place the returned resource into.
///
/// The returned `ResourceAny` will not have a destructor attached to it
/// meaning that if `resource_drop` is called then it will not invoked a
/// host-defined destructor. This is similar to how `Resource<T>` does not
/// have a destructor associated with it.
///
/// # Errors
///
/// This method will return an error if `resource` has already been "taken"
/// and has ownership transferred elsewhere which can happen in situations
/// such as when it's already lowered into a component.
pub fn try_from_resource<T: 'static>(
resource: Resource<T>,
mut store: impl AsContextMut,
) -> Result<Self> {
let Resource { rep, state, .. } = resource;
let store = store.as_context_mut();
let mut tables = HostResourceTables::new_host(store.0);
let (idx, owned) = match state.get() {
ResourceState::Borrow => (tables.host_resource_lower_borrow(rep)?, false),
ResourceState::NotInTable => {
let idx = tables.host_resource_lower_own(rep, None, None)?;
(idx, true)
}
ResourceState::Taken => bail!("host resource already consumed"),
ResourceState::Index(idx) => (idx, true),
};
Ok(Self {
idx,
ty: ResourceType::host::<T>(),
owned,
})
}
/// See [`Resource::try_from_resource_any`]
pub fn try_into_resource<T: 'static>(self, store: impl AsContextMut) -> Result<Resource<T>> {
Resource::try_from_resource_any(self, store)
}
/// Returns the corresponding type associated with this resource, either a
/// host-defined type or a guest-defined type.
///
/// This can be compared against [`ResourceType::host`] for example to see
/// if it's a host-resource or against a type extracted with
/// [`Instance::get_resource`] to see if it's a guest-defined resource.
///
/// [`Instance::get_resource`]: crate::component::Instance::get_resource
pub fn ty(&self) -> ResourceType {
self.ty
}
/// Returns whether this is an owned resource, and if not it's a borrowed
/// resource.
pub fn owned(&self) -> bool {
self.owned
}
/// Destroy this resource and release any state associated with it.
///
/// This is required to be called (or the async version) for all instances
/// of [`ResourceAny`] to ensure that state associated with this resource is
/// properly cleaned up. For owned resources this may execute the
/// guest-defined destructor if applicable (or the host-defined destructor
/// if one was specified).
pub fn resource_drop(self, mut store: impl AsContextMut) -> Result<()> {
let mut store = store.as_context_mut();
assert!(
!store.0.async_support(),
"must use `resource_drop_async` when async support is enabled on the config"
);
self.resource_drop_impl(&mut store.as_context_mut())
}
/// Same as [`ResourceAny::resource_drop`] except for use with async stores
/// to execute the destructor asynchronously.
#[cfg(feature = "async")]
pub async fn resource_drop_async<T>(self, mut store: impl AsContextMut<Data = T>) -> Result<()>
where
T: Send,
{
let mut store = store.as_context_mut();
assert!(
store.0.async_support(),
"cannot use `resource_drop_async` without enabling async support in the config"
);
store
.on_fiber(|store| self.resource_drop_impl(store))
.await?
}
fn resource_drop_impl<T>(self, store: &mut StoreContextMut<'_, T>) -> Result<()> {
// Attempt to remove `self.idx` from the host table in `store`.
//
// This could fail if the index is invalid or if this is removing an
// `Own` entry which is currently being borrowed.
let pair = HostResourceTables::new_host(store.0).host_resource_drop(self.idx)?;
let (rep, slot) = match (pair, self.owned) {
(Some(pair), true) => pair,
// A `borrow` was removed from the table and no further
// destruction, e.g. the destructor, is required so we're done.
(None, false) => return Ok(()),
_ => unreachable!(),
};
// Implement the reentrance check required by the canonical ABI. Note
// that this happens whether or not a destructor is present.
//
// Note that this should be safe because the raw pointer access in
// `flags` is valid due to `store` being the owner of the flags and
// flags are never destroyed within the store.
if let Some(flags) = slot.flags {
unsafe {
if !flags.may_enter() {
bail!(Trap::CannotEnterComponent);
}
}
}
let dtor = match slot.dtor {
Some(dtor) => dtor.as_non_null(),
None => return Ok(()),
};
let mut args = [ValRaw::u32(rep)];
// This should be safe because `dtor` has been checked to belong to the
// `store` provided which means it's valid and still alive. Additionally
// destructors have al been previously type-checked and are guaranteed
// to take one i32 argument and return no results, so the parameters
// here should be configured correctly.
unsafe { crate::Func::call_unchecked_raw(store, dtor, args.as_mut_ptr(), args.len()) }
}
fn lower_to_index<U>(&self, cx: &mut LowerContext<'_, U>, ty: InterfaceType) -> Result<u32> {
match ty {
InterfaceType::Own(t) => {
if cx.resource_type(t) != self.ty {
bail!("mismatched resource types");
}
let rep = cx.host_resource_lift_own(self.idx)?;
cx.guest_resource_lower_own(t, rep)
}
InterfaceType::Borrow(t) => {
if cx.resource_type(t) != self.ty {
bail!("mismatched resource types");
}
let rep = cx.host_resource_lift_borrow(self.idx)?;
cx.guest_resource_lower_borrow(t, rep)
}
_ => bad_type_info(),
}
}
fn lift_from_index(cx: &mut LiftContext<'_>, ty: InterfaceType, index: u32) -> Result<Self> {
match ty {
InterfaceType::Own(t) => {
let ty = cx.resource_type(t);
let (rep, dtor, flags) = cx.guest_resource_lift_own(t, index)?;
let idx = cx.host_resource_lower_own(rep, dtor, flags)?;
Ok(ResourceAny {
idx,
ty,
owned: true,
})
}
InterfaceType::Borrow(t) => {
let ty = cx.resource_type(t);
let rep = cx.guest_resource_lift_borrow(t, index)?;
let idx = cx.host_resource_lower_borrow(rep)?;
Ok(ResourceAny {
idx,
ty,
owned: false,
})
}
_ => bad_type_info(),
}
}
}
unsafe impl ComponentType for ResourceAny {
const ABI: CanonicalAbiInfo = CanonicalAbiInfo::SCALAR4;
type Lower = <u32 as ComponentType>::Lower;
fn typecheck(ty: &InterfaceType, _types: &InstanceType<'_>) -> Result<()> {
match ty {
InterfaceType::Own(_) | InterfaceType::Borrow(_) => Ok(()),
other => bail!("expected `own` or `borrow`, found `{}`", desc(other)),
}
}
}
unsafe impl Lower for ResourceAny {
fn lower<T>(
&self,
cx: &mut LowerContext<'_, T>,
ty: InterfaceType,
dst: &mut MaybeUninit<Self::Lower>,
) -> Result<()> {
self.lower_to_index(cx, ty)?
.lower(cx, InterfaceType::U32, dst)
}
fn store<T>(
&self,
cx: &mut LowerContext<'_, T>,
ty: InterfaceType,
offset: usize,
) -> Result<()> {
self.lower_to_index(cx, ty)?
.store(cx, InterfaceType::U32, offset)
}
}
unsafe impl Lift for ResourceAny {
fn lift(cx: &mut LiftContext<'_>, ty: InterfaceType, src: &Self::Lower) -> Result<Self> {
let index = u32::lift(cx, InterfaceType::U32, src)?;
ResourceAny::lift_from_index(cx, ty, index)
}
fn load(cx: &mut LiftContext<'_>, ty: InterfaceType, bytes: &[u8]) -> Result<Self> {
let index = u32::load(cx, InterfaceType::U32, bytes)?;
ResourceAny::lift_from_index(cx, ty, index)
}
}