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use core::marker::PhantomData;
use js_sys::Promise;
use wasm_bindgen::prelude::*;
use super::raw::util::UninitCell;
use super::raw::{self};
use super::Spawner;
/// WASM executor, wasm_bindgen to schedule tasks on the JS event loop.
pub struct Executor {
inner: raw::Executor,
ctx: &'static WasmContext,
not_send: PhantomData<*mut ()>,
}
pub(crate) struct WasmContext {
promise: Promise,
closure: UninitCell<Closure<dyn FnMut(JsValue)>>,
}
impl WasmContext {
pub fn new() -> Self {
Self {
promise: Promise::resolve(&JsValue::undefined()),
closure: UninitCell::uninit(),
}
}
}
impl Executor {
/// Create a new Executor.
pub fn new() -> Self {
let ctx = &*Box::leak(Box::new(WasmContext::new()));
let inner = raw::Executor::new(
|p| unsafe {
let ctx = &*(p as *const () as *const WasmContext);
let _ = ctx.promise.then(ctx.closure.as_mut());
},
ctx as *const _ as _,
);
Self {
inner,
not_send: PhantomData,
ctx,
}
}
/// Run the executor.
///
/// The `init` closure is called with a [`Spawner`] that spawns tasks on
/// this executor. Use it to spawn the initial task(s). After `init` returns,
/// the executor starts running the tasks.
///
/// To spawn more tasks later, you may keep copies of the [`Spawner`] (it is `Copy`),
/// for example by passing it as an argument to the initial tasks.
///
/// This function requires `&'static mut self`. This means you have to store the
/// Executor instance in a place where it'll live forever and grants you mutable
/// access. There's a few ways to do this:
///
/// - a [Forever](crate::util::Forever) (safe)
/// - a `static mut` (unsafe)
/// - a local variable in a function you know never returns (like `fn main() -> !`), upgrading its lifetime with `transmute`. (unsafe)
pub fn start(&'static mut self, init: impl FnOnce(Spawner)) {
unsafe {
let executor = &self.inner;
self.ctx.closure.write(Closure::new(move |_| {
executor.poll();
}));
init(self.inner.spawner());
}
}
}
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