Traditional route appears to work

Beginnings of dylib extensions, entirely untestted

orchid-base/src/binary.rs

@@ -0,0 +1,118 @@
+use std::pin::Pin;
+use std::rc::Rc;
+use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
+
+use orchid_api::binary::{FutureContextVT, FutureVT, OwnedWakerVT, UnitPoll};
+
+type WideBox = Box<dyn Future<Output = ()>>;
+
+static OWNED_VTABLE: RawWakerVTable = RawWakerVTable::new(
+	|data| {
+		let data = unsafe { Rc::<OwnedWakerVT>::from_raw(data as *const _) };
+		let val = RawWaker::new(Rc::into_raw(data.clone()) as *const (), &OWNED_VTABLE);
+		// Clone must create a duplicate of the Rc, so it has to be un-leaked, cloned,
+		// then leaked again.
+		let _ = Rc::into_raw(data);
+		val
+	},
+	|data| {
+		// Wake must awaken the task and then clean up the state, so the waker must be
+		// un-leaked
+		let data = unsafe { Rc::<OwnedWakerVT>::from_raw(data as *const _) };
+		(data.wake)(data.data);
+	},
+	|data| {
+		// Wake-by-ref must awaken the task while preserving the future, so the Rc is
+		// untouched
+		let data = unsafe { (data as *const OwnedWakerVT).as_ref() }.unwrap();
+		(data.wake_ref)(data.data);
+	},
+	|data| {
+		// Drop must clean up the state, so the waker must be un-leaked
+		let data = unsafe { Rc::<OwnedWakerVT>::from_raw(data as *const _) };
+		(data.drop)(data.data);
+	},
+);
+
+struct BorrowedWakerData<'a> {
+	go_around: &'a mut bool,
+	cx: FutureContextVT,
+}
+static BORROWED_VTABLE: RawWakerVTable = RawWakerVTable::new(
+	|data| {
+		let data = unsafe { (data as *mut BorrowedWakerData).as_mut() }.unwrap();
+		let owned_data = Rc::<OwnedWakerVT>::new((data.cx.waker)(data.cx.data));
+		RawWaker::new(Rc::into_raw(owned_data) as *const (), &OWNED_VTABLE)
+	},
+	|data| *unsafe { (data as *mut BorrowedWakerData).as_mut() }.unwrap().go_around = true,
+	|data| *unsafe { (data as *mut BorrowedWakerData).as_mut() }.unwrap().go_around = true,
+	|_data| {},
+);
+
+/// Convert a future to a binary-compatible format that can be sent across
+/// dynamic library boundaries
+pub fn future_to_vt<Fut: Future<Output = ()> + 'static>(fut: Fut) -> FutureVT {
+	let wide_box = Box::new(fut) as WideBox;
+	let data = Box::into_raw(Box::new(wide_box));
+	extern "C" fn drop(raw: *const ()) {
+		std::mem::drop(unsafe { Box::<WideBox>::from_raw(raw as *mut _) })
+	}
+	extern "C" fn poll(raw: *const (), cx: FutureContextVT) -> UnitPoll {
+		let mut this = unsafe { Pin::new_unchecked(&mut **(raw as *mut WideBox).as_mut().unwrap()) };
+		loop {
+			let mut go_around = false;
+			let borrowed_waker = unsafe {
+				Waker::from_raw(RawWaker::new(
+					&mut BorrowedWakerData { go_around: &mut go_around, cx } as *mut _ as *const (),
+					&BORROWED_VTABLE,
+				))
+			};
+			let mut ctx = Context::from_waker(&borrowed_waker);
+			let result = this.as_mut().poll(&mut ctx);
+			if matches!(result, Poll::Ready(())) {
+				break UnitPoll::Ready;
+			}
+			if !go_around {
+				break UnitPoll::Pending;
+			}
+		}
+	}
+	FutureVT { data: data as *const _, drop, poll }
+}
+
+struct VirtualFuture {
+	vt: FutureVT,
+}
+impl Unpin for VirtualFuture {}
+impl Future for VirtualFuture {
+	type Output = ();
+	fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+		extern "C" fn waker(raw: *const ()) -> OwnedWakerVT {
+			let waker = unsafe { (raw as *mut Context).as_mut() }.unwrap().waker().clone();
+			let data = Box::into_raw(Box::<Waker>::new(waker)) as *const ();
+			return OwnedWakerVT { data, drop, wake, wake_ref };
+			extern "C" fn drop(raw: *const ()) {
+				std::mem::drop(unsafe { Box::<Waker>::from_raw(raw as *mut Waker) })
+			}
+			extern "C" fn wake(raw: *const ()) {
+				unsafe { Box::<Waker>::from_raw(raw as *mut Waker) }.wake();
+			}
+			extern "C" fn wake_ref(raw: *const ()) {
+				unsafe { (raw as *mut Waker).as_mut() }.unwrap().wake_by_ref();
+			}
+		}
+		let cx = FutureContextVT { data: cx as *mut Context as *const (), waker };
+		let result = (self.vt.poll)(self.vt.data, cx);
+		match result {
+			UnitPoll::Pending => Poll::Pending,
+			UnitPoll::Ready => Poll::Ready(()),
+		}
+	}
+}
+impl Drop for VirtualFuture {
+	fn drop(&mut self) { (self.vt.drop)(self.vt.data) }
+}
+
+/// Receive a future sent across dynamic library boundaries and convert it into
+/// an owned object
+pub fn vt_to_future(vt: FutureVT) -> impl Future<Output = ()> { VirtualFuture { vt } }