1 files changed, 74 insertions, 0 deletions

diff --git a/embassy-executor/src/executor/arch/wasm.rs b/embassy-executor/src/executor/arch/wasm.rs
new file mode 100644
index 000000000..9d5aa31ed
--- /dev/null
+++ b/embassy-executor/src/executor/arch/wasm.rs
@@ -0,0 +1,74 @@
+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());
+        }
+    }
+}