+#[cfg(feature = "futures")]
+pub(crate) mod futures_util {
+ use core::future::Future;
+ use core::task::{Poll, Waker, RawWaker, RawWakerVTable};
+ use core::pin::Pin;
+ use core::marker::Unpin;
+ pub(crate) struct Selector<
+ A: Future<Output=()> + Unpin, B: Future<Output=()> + Unpin, C: Future<Output=bool> + Unpin
+ > {
+ pub a: A,
+ pub b: B,
+ pub c: C,
+ }
+ pub(crate) enum SelectorOutput {
+ A, B, C(bool),
+ }
+
+ impl<
+ A: Future<Output=()> + Unpin, B: Future<Output=()> + Unpin, C: Future<Output=bool> + Unpin
+ > Future for Selector<A, B, C> {
+ type Output = SelectorOutput;
+ fn poll(mut self: Pin<&mut Self>, ctx: &mut core::task::Context<'_>) -> Poll<SelectorOutput> {
+ match Pin::new(&mut self.a).poll(ctx) {
+ Poll::Ready(()) => { return Poll::Ready(SelectorOutput::A); },
+ Poll::Pending => {},
+ }
+ match Pin::new(&mut self.b).poll(ctx) {
+ Poll::Ready(()) => { return Poll::Ready(SelectorOutput::B); },
+ Poll::Pending => {},
+ }
+ match Pin::new(&mut self.c).poll(ctx) {
+ Poll::Ready(res) => { return Poll::Ready(SelectorOutput::C(res)); },
+ Poll::Pending => {},
+ }
+ Poll::Pending
+ }
+ }
+
+ // If we want to poll a future without an async context to figure out if it has completed or
+ // not without awaiting, we need a Waker, which needs a vtable...we fill it with dummy values
+ // but sadly there's a good bit of boilerplate here.
+ fn dummy_waker_clone(_: *const ()) -> RawWaker { RawWaker::new(core::ptr::null(), &DUMMY_WAKER_VTABLE) }
+ fn dummy_waker_action(_: *const ()) { }
+
+ const DUMMY_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(
+ dummy_waker_clone, dummy_waker_action, dummy_waker_action, dummy_waker_action);
+ pub(crate) fn dummy_waker() -> Waker { unsafe { Waker::from_raw(RawWaker::new(core::ptr::null(), &DUMMY_WAKER_VTABLE)) } }
+}
+#[cfg(feature = "futures")]
+use futures_util::{Selector, SelectorOutput, dummy_waker};
+#[cfg(feature = "futures")]
+use core::task;
+