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    // 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.

    //! Types and Traits for working with asynchronous tasks.

    pub use core::task::*;

    #[cfg(any(
        all(stage0, target_has_atomic = "ptr"),
        all(not(stage0), target_has_atomic = "ptr", target_has_atomic = "cas")
    ))]
    pub use self::if_arc::*;

    #[cfg(any(
        all(stage0, target_has_atomic = "ptr"),
        all(not(stage0), target_has_atomic = "ptr", target_has_atomic = "cas")
    ))]
    mod if_arc {
        use super::*;
        use core::marker::PhantomData;
        use core::mem;
        use core::ptr::{self, NonNull};
        use sync::Arc;

        /// A way of waking up a specific task.
        ///
        /// Any task executor must provide a way of signaling that a task it owns
        /// is ready to be `poll`ed again. Executors do so by implementing this trait.
        pub trait Wake: Send + Sync {
            /// Indicates that the associated task is ready to make progress and should
            /// be `poll`ed.
            ///
            /// Executors generally maintain a queue of "ready" tasks; `wake` should place
            /// the associated task onto this queue.
            fn wake(arc_self: &Arc<Self>);

            /// Indicates that the associated task is ready to make progress and should
            /// be `poll`ed. This function is like `wake`, but can only be called from the
            /// thread on which this `Wake` was created.
            ///
            /// Executors generally maintain a queue of "ready" tasks; `wake_local` should place
            /// the associated task onto this queue.
            #[inline]
            unsafe fn wake_local(arc_self: &Arc<Self>) {
                Self::wake(arc_self);
            }
        }

        #[cfg(any(
            all(stage0, target_has_atomic = "ptr"),
            all(not(stage0), target_has_atomic = "ptr", target_has_atomic = "cas")
        ))]
        struct ArcWrapped<T>(PhantomData<T>);

        unsafe impl<T: Wake + 'static> UnsafeWake for ArcWrapped<T> {
            #[inline]
            unsafe fn clone_raw(&self) -> Waker {
                let me: *const ArcWrapped<T> = self;
                let arc = (*(&me as *const *const ArcWrapped<T> as *const Arc<T>)).clone();
                Waker::from(arc)
            }

            #[inline]
            unsafe fn drop_raw(&self) {
                let mut me: *const ArcWrapped<T> = self;
                let me = &mut me as *mut *const ArcWrapped<T> as *mut Arc<T>;
                ptr::drop_in_place(me);
            }

            #[inline]
            unsafe fn wake(&self) {
                let me: *const ArcWrapped<T> = self;
                T::wake(&*(&me as *const *const ArcWrapped<T> as *const Arc<T>))
            }

            #[inline]
            unsafe fn wake_local(&self) {
                let me: *const ArcWrapped<T> = self;
                T::wake_local(&*(&me as *const *const ArcWrapped<T> as *const Arc<T>))
            }
        }

        impl<T> From<Arc<T>> for Waker
            where T: Wake + 'static,
        {
            fn from(rc: Arc<T>) -> Self {
                unsafe {
                    let ptr = mem::transmute::<Arc<T>, NonNull<ArcWrapped<T>>>(rc);
                    Waker::new(ptr)
                }
            }
        }

        /// Creates a `LocalWaker` from a local `wake`.
        ///
        /// This function requires that `wake` is "local" (created on the current thread).
        /// The resulting `LocalWaker` will call `wake.wake_local()` when awoken, and
        /// will call `wake.wake()` if awoken after being converted to a `Waker`.
        #[inline]
        pub unsafe fn local_waker<W: Wake + 'static>(wake: Arc<W>) -> LocalWaker {
            let ptr = mem::transmute::<Arc<W>, NonNull<ArcWrapped<W>>>(wake);
            LocalWaker::new(ptr)
        }

        struct NonLocalAsLocal<T>(ArcWrapped<T>);

        unsafe impl<T: Wake + 'static> UnsafeWake for NonLocalAsLocal<T> {
            #[inline]
            unsafe fn clone_raw(&self) -> Waker {
                self.0.clone_raw()
            }

            #[inline]
            unsafe fn drop_raw(&self) {
                self.0.drop_raw()
            }

            #[inline]
            unsafe fn wake(&self) {
                self.0.wake()
            }

            #[inline]
            unsafe fn wake_local(&self) {
                // Since we're nonlocal, we can't call wake_local
                self.0.wake()
            }
        }

        /// Creates a `LocalWaker` from a non-local `wake`.
        ///
        /// This function is similar to `local_waker`, but does not require that `wake`
        /// is local to the current thread. The resulting `LocalWaker` will call
        /// `wake.wake()` when awoken.
        #[inline]
        pub fn local_waker_from_nonlocal<W: Wake + 'static>(wake: Arc<W>) -> LocalWaker {
            unsafe {
                let ptr = mem::transmute::<Arc<W>, NonNull<NonLocalAsLocal<W>>>(wake);
                LocalWaker::new(ptr)
            }
        }
    }

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