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#[cfg(bootstrap)]
use core::{
cell::Cell,
marker::Unpin,
ops::{Drop, Generator, GeneratorState},
pin::Pin,
ptr::NonNull,
task::{Context, Poll},
};
#[doc(inline)]
pub use core::future::*;
#[cfg(bootstrap)]
#[doc(hidden)]
pub const fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
GenFuture(x)
}
#[cfg(bootstrap)]
#[doc(hidden)]
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
struct GenFuture<T: Generator<Yield = ()>>(T);
#[cfg(bootstrap)]
impl<T: Generator<Yield = ()>> !Unpin for GenFuture<T> {}
#[cfg(bootstrap)]
#[doc(hidden)]
impl<T: Generator<Yield = ()>> Future for GenFuture<T> {
type Output = T::Return;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let gen = unsafe { Pin::map_unchecked_mut(self, |s| &mut s.0) };
let _guard = unsafe { set_task_context(cx) };
match gen.resume(()) {
GeneratorState::Yielded(()) => Poll::Pending,
GeneratorState::Complete(x) => Poll::Ready(x),
}
}
}
#[cfg(bootstrap)]
thread_local! {
static TLS_CX: Cell<Option<NonNull<Context<'static>>>> = Cell::new(None);
}
#[cfg(bootstrap)]
struct SetOnDrop(Option<NonNull<Context<'static>>>);
#[cfg(bootstrap)]
impl Drop for SetOnDrop {
fn drop(&mut self) {
TLS_CX.with(|tls_cx| {
tls_cx.set(self.0.take());
});
}
}
#[cfg(bootstrap)]
unsafe fn set_task_context(cx: &mut Context<'_>) -> SetOnDrop {
let cx = core::mem::transmute::<&mut Context<'_>, &mut Context<'static>>(cx);
let old_cx = TLS_CX.with(|tls_cx| tls_cx.replace(Some(NonNull::from(cx))));
SetOnDrop(old_cx)
}
#[cfg(bootstrap)]
#[doc(hidden)]
pub fn poll_with_tls_context<F>(f: Pin<&mut F>) -> Poll<F::Output>
where
F: Future,
{
let cx_ptr = TLS_CX.with(|tls_cx| {
tls_cx.replace(None)
});
let _reset = SetOnDrop(cx_ptr);
let mut cx_ptr = cx_ptr.expect(
"TLS Context not set. This is a rustc bug. \
Please file an issue on https://github.com/rust-lang/rust.",
);
unsafe { F::poll(f, cx_ptr.as_mut()) }
}