Struct wasmtime_wasi::preview2::Table

pub struct Table { /* private fields */ }

The Table type is designed to map u32 handles to resources. The table is now part of the public interface to a WasiCtx - it is reference counted so that it can be shared beyond a WasiCtx with other WASI proposals (e.g. wasi-crypto and wasi-nn) to manage their resources. Elements in the Table are Any typed.

The Table type is intended to model how the Interface Types concept of Resources is shaping up. Right now it is just an approximation.

Implementations

impl Table

pub fn new() -> Self

Create an empty table

pub fn push( &mut self, entry: Box<dyn Any + Send + Sync> ) -> Result<u32, TableError>

Insert a resource at the next available index.

pub fn push_resource<T>(&mut self, entry: T) -> Result<Resource<T>, TableError>

where T: Send + Sync + 'static,

Same as push, but typed.

pub fn push_child( &mut self, entry: Box<dyn Any + Send + Sync>, parent: u32 ) -> Result<u32, TableError>

Insert a resource at the next available index, and track that it has a parent resource.

The parent must exist to create a child. All children resources must be destroyed before a parent can be destroyed - otherwise Table::delete will fail with TableError::HasChildren.

Parent-child relationships are tracked inside the table to ensure that a parent resource is not deleted while it has live children. This allows child resources to hold “references” to a parent by table index, to avoid needing e.g. an Arc<Mutex<parent>> and the associated locking overhead and design issues, such as child existence extending lifetime of parent referent even after parent resource is destroyed, possibility for deadlocks.

Parent-child relationships may not be modified once created. There is no way to observe these relationships through the Table methods except for erroring on deletion, or the std::fmt::Debug impl.

pub fn push_child_resource<T, U>( &mut self, entry: T, parent: &Resource<U> ) -> Result<Resource<T>, TableError>

where T: Send + Sync + 'static, U: 'static,

Same as push_child, but typed.

pub fn contains_key(&self, key: u32) -> bool

Check if the table has a resource at the given index.

pub fn is<T: Any + Sized>(&self, key: u32) -> bool

Check if the resource at a given index can be downcast to a given type. Note: this will always fail if the resource is already borrowed.

pub fn get_any_mut(&mut self, key: u32) -> Result<&mut dyn Any, TableError>

Get a mutable reference to the underlying untyped cell for an entry in the table.

pub fn get<T: Any + Sized>(&self, key: u32) -> Result<&T, TableError>

Get an immutable reference to a resource of a given type at a given index. Multiple immutable references can be borrowed at any given time. Borrow failure results in a trapping error.

pub fn get_mut<T: Any + Sized>( &mut self, key: u32 ) -> Result<&mut T, TableError>

Get a mutable reference to a resource of a given type at a given index.

pub fn get_as_any_mut(&mut self, key: u32) -> Result<&mut dyn Any, TableError>

Get a mutable reference to a resource a a &mut dyn Any.

pub fn get_resource<T: Any + Sized>( &self, key: &Resource<T> ) -> Result<&T, TableError>

Same as get, but typed

pub fn get_resource_mut<T: Any + Sized>( &mut self, key: &Resource<T> ) -> Result<&mut T, TableError>

Same as get_mut, but typed

pub fn delete<T: Any + Sized>(&mut self, key: u32) -> Result<T, TableError>

Remove a resource at a given index from the table.

If this method fails, the resource remains in the table.

May fail with TableError::HasChildren if the resource has any live children.

pub fn delete_resource<T>( &mut self, resource: Resource<T> ) -> Result<T, TableError>

where T: Any,

Same as delete, but typed

pub fn iter_entries<'a, T>( &'a mut self, map: HashMap<u32, T> ) -> impl Iterator<Item = (Result<&'a mut dyn Any, TableError>, T)>

Zip the values of the map with mutable references to table entries corresponding to each key. As the keys in the HashMap are unique, this iterator can give mutable references with the same lifetime as the mutable reference to the Table.

Trait Implementations

impl Debug for Table

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Table

fn default() -> Self

Returns the “default value” for a type.