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use core::cell::Cell;
use core::marker::Unpin;
use core::pin::Pin;
use core::option::Option;
use core::ptr::NonNull;
use core::task::{Context, Poll};
use core::ops::{Drop, Generator, GeneratorState};
#[doc(inline)]
#[stable(feature = "futures_api", since = "1.36.0")]
pub use core::future::*;
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
pub fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
GenFuture(x)
}
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[cfg_attr(all(not(test), not(bootstrap)), rustc_diagnostic_item = "gen_future")]
struct GenFuture<T: Generator<Yield = ()>>(T);
impl<T: Generator<Yield = ()>> !Unpin for GenFuture<T> {}
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
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) };
set_task_context(cx, || match gen.resume() {
GeneratorState::Yielded(()) => Poll::Pending,
GeneratorState::Complete(x) => Poll::Ready(x),
})
}
}
thread_local! {
static TLS_CX: Cell<Option<NonNull<Context<'static>>>> = Cell::new(None);
}
struct SetOnDrop(Option<NonNull<Context<'static>>>);
impl Drop for SetOnDrop {
fn drop(&mut self) {
TLS_CX.with(|tls_cx| {
tls_cx.set(self.0.take());
});
}
}
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
pub fn set_task_context<F, R>(cx: &mut Context<'_>, f: F) -> R
where
F: FnOnce() -> R
{
let cx = unsafe {
core::mem::transmute::<&mut Context<'_>, &mut Context<'static>>(cx)
};
let old_cx = TLS_CX.with(|tls_cx| {
tls_cx.replace(Some(NonNull::from(cx)))
});
let _reset = SetOnDrop(old_cx);
f()
}
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
pub fn get_task_context<F, R>(f: F) -> R
where
F: FnOnce(&mut Context<'_>) -> R
{
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(cx_ptr.as_mut()) }
}
#[doc(hidden)]
#[unstable(feature = "gen_future", issue = "50547")]
pub fn poll_with_tls_context<F>(f: Pin<&mut F>) -> Poll<F::Output>
where
F: Future
{
get_task_context(|cx| F::poll(f, cx))
}