From 5d28bfcfd6086c3328837de9695099ea39048d0d Mon Sep 17 00:00:00 2001
From: Fenrir <fenrirwolf@gmail.com>
Date: Sun, 19 Aug 2018 17:48:00 -0600
Subject: Update for nightly-2018-08-18

---
 ctr-std/src/future.rs | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 ctr-std/src/future.rs

(limited to 'ctr-std/src/future.rs')

diff --git a/ctr-std/src/future.rs b/ctr-std/src/future.rs
new file mode 100644
index 0000000..12ea1ea
--- /dev/null
+++ b/ctr-std/src/future.rs
@@ -0,0 +1,116 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Asynchronous values.
+
+use core::cell::Cell;
+use core::marker::Unpin;
+use core::mem::PinMut;
+use core::option::Option;
+use core::ptr::NonNull;
+use core::task::{self, Poll};
+use core::ops::{Drop, Generator, GeneratorState};
+
+#[doc(inline)]
+pub use core::future::*;
+
+/// Wrap a future in a generator.
+///
+/// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give
+/// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`).
+#[unstable(feature = "gen_future", issue = "50547")]
+pub fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
+    GenFuture(x)
+}
+
+/// A wrapper around generators used to implement `Future` for `async`/`await` code.
+#[unstable(feature = "gen_future", issue = "50547")]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+struct GenFuture<T: Generator<Yield = ()>>(T);
+
+// We rely on the fact that async/await futures are immovable in order to create
+// self-referential borrows in the underlying generator.
+impl<T: Generator<Yield = ()>> !Unpin for GenFuture<T> {}
+
+#[unstable(feature = "gen_future", issue = "50547")]
+impl<T: Generator<Yield = ()>> Future for GenFuture<T> {
+    type Output = T::Return;
+    fn poll(self: PinMut<Self>, cx: &mut task::Context) -> Poll<Self::Output> {
+        set_task_cx(cx, || match unsafe { PinMut::get_mut_unchecked(self).0.resume() } {
+            GeneratorState::Yielded(()) => Poll::Pending,
+            GeneratorState::Complete(x) => Poll::Ready(x),
+        })
+    }
+}
+
+thread_local! {
+    static TLS_CX: Cell<Option<NonNull<task::Context<'static>>>> = Cell::new(None);
+}
+
+struct SetOnDrop(Option<NonNull<task::Context<'static>>>);
+
+impl Drop for SetOnDrop {
+    fn drop(&mut self) {
+        TLS_CX.with(|tls_cx| {
+            tls_cx.set(self.0.take());
+        });
+    }
+}
+
+#[unstable(feature = "gen_future", issue = "50547")]
+/// Sets the thread-local task context used by async/await futures.
+pub fn set_task_cx<F, R>(cx: &mut task::Context, f: F) -> R
+where
+    F: FnOnce() -> R
+{
+    let old_cx = TLS_CX.with(|tls_cx| {
+        tls_cx.replace(NonNull::new(
+            cx
+                as *mut task::Context
+                as *mut ()
+                as *mut task::Context<'static>
+        ))
+    });
+    let _reset_cx = SetOnDrop(old_cx);
+    f()
+}
+
+#[unstable(feature = "gen_future", issue = "50547")]
+/// Retrieves the thread-local task context used by async/await futures.
+///
+/// This function acquires exclusive access to the task context.
+///
+/// Panics if no task has been set or if the task context has already been
+/// retrived by a surrounding call to get_task_cx.
+pub fn get_task_cx<F, R>(f: F) -> R
+where
+    F: FnOnce(&mut task::Context) -> R
+{
+    let cx_ptr = TLS_CX.with(|tls_cx| {
+        // Clear the entry so that nested `with_get_cx` calls
+        // will fail or set their own value.
+        tls_cx.replace(None)
+    });
+    let _reset_cx = SetOnDrop(cx_ptr);
+
+    let mut cx_ptr = cx_ptr.expect(
+        "TLS task::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()) }
+}
+
+#[unstable(feature = "gen_future", issue = "50547")]
+/// Polls a future in the current thread-local task context.
+pub fn poll_in_task_cx<F>(f: PinMut<F>) -> Poll<F::Output>
+where
+    F: Future
+{
+    get_task_cx(|cx| f.poll(cx))
+}
-- 
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