1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245
use crate::{bindings::io::poll, WasiImpl, WasiView};
use anyhow::{anyhow, Result};
use std::any::Any;
use std::collections::HashMap;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use wasmtime::component::{Resource, ResourceTable};
pub type PollableFuture<'a> = Pin<Box<dyn Future<Output = ()> + Send + 'a>>;
pub type MakeFuture = for<'a> fn(&'a mut dyn Any) -> PollableFuture<'a>;
pub type ClosureFuture = Box<dyn Fn() -> PollableFuture<'static> + Send + 'static>;
/// A host representation of the `wasi:io/poll.pollable` resource.
///
/// A pollable is not the same thing as a Rust Future: the same pollable may be used to
/// repeatedly check for readiness of a given condition, e.g. if a stream is readable
/// or writable. So, rather than containing a Future, which can only become Ready once, a
/// Pollable contains a way to create a Future in each call to `poll`.
pub struct Pollable {
index: u32,
make_future: MakeFuture,
remove_index_on_delete: Option<fn(&mut ResourceTable, u32) -> Result<()>>,
}
/// A trait used internally within a [`Pollable`] to create a `pollable`
/// resource in `wasi:io/poll`.
///
/// This trait is the internal implementation detail of any pollable resource in
/// this crate's implementation of WASI. The `ready` function is an `async fn`
/// which resolves when the implementation is ready. Using native `async` Rust
/// enables this type's readiness to compose with other types' readiness
/// throughout the WASI implementation.
///
/// This trait is used in conjunction with [`subscribe`] to create a `pollable`
/// resource.
///
/// # Example
///
/// This is a simple example of creating a `Pollable` resource from a few
/// parameters.
///
/// ```
/// use tokio::time::{self, Duration, Instant};
/// use wasmtime_wasi::{WasiView, Subscribe, subscribe, Pollable, async_trait};
/// use wasmtime::component::Resource;
/// use wasmtime::Result;
///
/// fn sleep(cx: &mut dyn WasiView, dur: Duration) -> Result<Resource<Pollable>> {
/// let end = Instant::now() + dur;
/// let sleep = MySleep { end };
/// let sleep_resource = cx.table().push(sleep)?;
/// subscribe(cx.table(), sleep_resource)
/// }
///
/// struct MySleep {
/// end: Instant,
/// }
///
/// #[async_trait]
/// impl Subscribe for MySleep {
/// async fn ready(&mut self) {
/// tokio::time::sleep_until(self.end).await;
/// }
/// }
/// ```
#[async_trait::async_trait]
pub trait Subscribe: Send + 'static {
/// An asynchronous function which resolves when this object's readiness
/// operation is ready.
///
/// This function is invoked as part of `poll` in `wasi:io/poll`. The
/// meaning of when this function Returns depends on what object this
/// [`Subscribe`] is attached to. When the returned future resolves then the
/// corresponding call to `wasi:io/poll` will return.
///
/// Note that this method does not return an error. Returning an error
/// should be done through accessors on the object that this `pollable` is
/// connected to. The call to `wasi:io/poll` itself does not return errors,
/// only a list of ready objects.
async fn ready(&mut self);
}
/// Creates a `pollable` resource which is subscribed to the provided
/// `resource`.
///
/// If `resource` is an owned resource then it will be deleted when the returned
/// resource is deleted. Otherwise the returned resource is considered a "child"
/// of the given `resource` which means that the given resource cannot be
/// deleted while the `pollable` is still alive.
pub fn subscribe<T>(table: &mut ResourceTable, resource: Resource<T>) -> Result<Resource<Pollable>>
where
T: Subscribe,
{
fn make_future<'a, T>(stream: &'a mut dyn Any) -> PollableFuture<'a>
where
T: Subscribe,
{
stream.downcast_mut::<T>().unwrap().ready()
}
let pollable = Pollable {
index: resource.rep(),
remove_index_on_delete: if resource.owned() {
Some(|table, idx| {
let resource = Resource::<T>::new_own(idx);
table.delete(resource)?;
Ok(())
})
} else {
None
},
make_future: make_future::<T>,
};
Ok(table.push_child(pollable, &resource)?)
}
#[async_trait::async_trait]
impl<T> poll::Host for WasiImpl<T>
where
T: WasiView,
{
async fn poll(&mut self, pollables: Vec<Resource<Pollable>>) -> Result<Vec<u32>> {
type ReadylistIndex = u32;
if pollables.is_empty() {
return Err(anyhow!("empty poll list"));
}
let table = self.table();
let mut table_futures: HashMap<u32, (MakeFuture, Vec<ReadylistIndex>)> = HashMap::new();
for (ix, p) in pollables.iter().enumerate() {
let ix: u32 = ix.try_into()?;
let pollable = table.get(p)?;
let (_, list) = table_futures
.entry(pollable.index)
.or_insert((pollable.make_future, Vec::new()));
list.push(ix);
}
let mut futures: Vec<(PollableFuture<'_>, Vec<ReadylistIndex>)> = Vec::new();
for (entry, (make_future, readylist_indices)) in table.iter_entries(table_futures) {
let entry = entry?;
futures.push((make_future(entry), readylist_indices));
}
struct PollList<'a> {
futures: Vec<(PollableFuture<'a>, Vec<ReadylistIndex>)>,
}
impl<'a> Future for PollList<'a> {
type Output = Vec<u32>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut any_ready = false;
let mut results = Vec::new();
for (fut, readylist_indicies) in self.futures.iter_mut() {
match fut.as_mut().poll(cx) {
Poll::Ready(()) => {
results.extend_from_slice(readylist_indicies);
any_ready = true;
}
Poll::Pending => {}
}
}
if any_ready {
Poll::Ready(results)
} else {
Poll::Pending
}
}
}
Ok(PollList { futures }.await)
}
}
#[async_trait::async_trait]
impl<T> crate::bindings::io::poll::HostPollable for WasiImpl<T>
where
T: WasiView,
{
async fn block(&mut self, pollable: Resource<Pollable>) -> Result<()> {
let table = self.table();
let pollable = table.get(&pollable)?;
let ready = (pollable.make_future)(table.get_any_mut(pollable.index)?);
ready.await;
Ok(())
}
async fn ready(&mut self, pollable: Resource<Pollable>) -> Result<bool> {
let table = self.table();
let pollable = table.get(&pollable)?;
let ready = (pollable.make_future)(table.get_any_mut(pollable.index)?);
futures::pin_mut!(ready);
Ok(matches!(
futures::future::poll_immediate(ready).await,
Some(())
))
}
fn drop(&mut self, pollable: Resource<Pollable>) -> Result<()> {
let pollable = self.table().delete(pollable)?;
if let Some(delete) = pollable.remove_index_on_delete {
delete(self.table(), pollable.index)?;
}
Ok(())
}
}
pub mod sync {
use crate::{
bindings::io::poll as async_poll,
bindings::sync::io::poll::{self, Pollable},
runtime::in_tokio,
WasiImpl, WasiView,
};
use anyhow::Result;
use wasmtime::component::Resource;
impl<T> poll::Host for WasiImpl<T>
where
T: WasiView,
{
fn poll(&mut self, pollables: Vec<Resource<Pollable>>) -> Result<Vec<u32>> {
in_tokio(async { async_poll::Host::poll(self, pollables).await })
}
}
impl<T> crate::bindings::sync::io::poll::HostPollable for WasiImpl<T>
where
T: WasiView,
{
fn ready(&mut self, pollable: Resource<Pollable>) -> Result<bool> {
in_tokio(async { async_poll::HostPollable::ready(self, pollable).await })
}
fn block(&mut self, pollable: Resource<Pollable>) -> Result<()> {
in_tokio(async { async_poll::HostPollable::block(self, pollable).await })
}
fn drop(&mut self, pollable: Resource<Pollable>) -> Result<()> {
async_poll::HostPollable::drop(self, pollable)
}
}
}