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    mod core;
    use self::core::Cell;
    pub(crate) use self::core::Header;

    mod error;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::error::JoinError;

    mod harness;
    use self::harness::Harness;

    mod join;
    #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
    pub use self::join::JoinHandle;

    mod raw;
    use self::raw::RawTask;

    mod state;
    use self::state::State;

    mod waker;

    cfg_rt_multi_thread! {
        mod stack;
        pub(crate) use self::stack::TransferStack;
    }

    use crate::util::linked_list;

    use std::future::Future;
    use std::marker::PhantomData;
    use std::ptr::NonNull;
    use std::{fmt, mem};

    /// An owned handle to the task, tracked by ref count
    #[repr(transparent)]
    pub(crate) struct Task<S: 'static> {
        raw: RawTask,
        _p: PhantomData<S>,
    }

    unsafe impl<S> Send for Task<S> {}
    unsafe impl<S> Sync for Task<S> {}

    /// A task was notified
    #[repr(transparent)]
    pub(crate) struct Notified<S: 'static>(Task<S>);

    unsafe impl<S: Schedule> Send for Notified<S> {}
    unsafe impl<S: Schedule> Sync for Notified<S> {}

    /// Task result sent back
    pub(crate) type Result<T> = std::result::Result<T, JoinError>;

    pub(crate) trait Schedule: Sync + Sized + 'static {
        /// Bind a task to the executor.
        ///
        /// Guaranteed to be called from the thread that called `poll` on the task.
        /// The returned `Schedule` instance is associated with the task and is used
        /// as `&self` in the other methods on this trait.
        fn bind(task: Task<Self>) -> Self;

        /// The task has completed work and is ready to be released. The scheduler
        /// is free to drop it whenever.
        ///
        /// If the scheduler can immediately release the task, it should return
        /// it as part of the function. This enables the task module to batch
        /// the ref-dec with other options.
        fn release(&self, task: &Task<Self>) -> Option<Task<Self>>;

        /// Schedule the task
        fn schedule(&self, task: Notified<Self>);

        /// Schedule the task to run in the near future, yielding the thread to
        /// other tasks.
        fn yield_now(&self, task: Notified<Self>) {
            self.schedule(task);
        }
    }

    cfg_rt! {
        /// Create a new task with an associated join handle
        pub(crate) fn joinable<T, S>(task: T) -> (Notified<S>, JoinHandle<T::Output>)
        where
            T: Future + Send + 'static,
            S: Schedule,
        {
            let raw = RawTask::new::<_, S>(task);

            let task = Task {
                raw,
                _p: PhantomData,
            };

            let join = JoinHandle::new(raw);

            (Notified(task), join)
        }
    }

    cfg_rt! {
        /// Create a new `!Send` task with an associated join handle
        pub(crate) unsafe fn joinable_local<T, S>(task: T) -> (Notified<S>, JoinHandle<T::Output>)
        where
            T: Future + 'static,
            S: Schedule,
        {
            let raw = RawTask::new::<_, S>(task);

            let task = Task {
                raw,
                _p: PhantomData,
            };

            let join = JoinHandle::new(raw);

            (Notified(task), join)
        }
    }

    impl<S: 'static> Task<S> {
        pub(crate) unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
            Task {
                raw: RawTask::from_raw(ptr),
                _p: PhantomData,
            }
        }

        pub(crate) fn header(&self) -> &Header {
            self.raw.header()
        }
    }

    cfg_rt_multi_thread! {
        impl<S: 'static> Notified<S> {
            pub(crate) unsafe fn from_raw(ptr: NonNull<Header>) -> Notified<S> {
                Notified(Task::from_raw(ptr))
            }

            pub(crate) fn header(&self) -> &Header {
                self.0.header()
            }
        }

        impl<S: 'static> Task<S> {
            pub(crate) fn into_raw(self) -> NonNull<Header> {
                let ret = self.header().into();
                mem::forget(self);
                ret
            }
        }

        impl<S: 'static> Notified<S> {
            pub(crate) fn into_raw(self) -> NonNull<Header> {
                self.0.into_raw()
            }
        }
    }

    impl<S: Schedule> Task<S> {
        /// Pre-emptively cancel the task as part of the shutdown process.
        pub(crate) fn shutdown(&self) {
            self.raw.shutdown();
        }
    }

    impl<S: Schedule> Notified<S> {
        /// Run the task
        pub(crate) fn run(self) {
            self.0.raw.poll();
            mem::forget(self);
        }

        /// Pre-emptively cancel the task as part of the shutdown process.
        pub(crate) fn shutdown(self) {
            self.0.shutdown();
        }
    }

    impl<S: 'static> Drop for Task<S> {
        fn drop(&mut self) {
            // Decrement the ref count
            if self.header().state.ref_dec() {
                // Deallocate if this is the final ref count
                self.raw.dealloc();
            }
        }
    }

    impl<S> fmt::Debug for Task<S> {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(fmt, "Task({:p})", self.header())
        }
    }

    impl<S> fmt::Debug for Notified<S> {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(fmt, "task::Notified({:p})", self.0.header())
        }
    }

    /// # Safety
    ///
    /// Tasks are pinned
    unsafe impl<S> linked_list::Link for Task<S> {
        type Handle = Task<S>;
        type Target = Header;

        fn as_raw(handle: &Task<S>) -> NonNull<Header> {
            handle.header().into()
        }

        unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
            Task::from_raw(ptr)
        }

        unsafe fn pointers(target: NonNull<Header>) -> NonNull<linked_list::Pointers<Header>> {
            // Not super great as it avoids some of looms checking...
            NonNull::from(target.as_ref().owned.with_mut(|ptr| &mut *ptr))
        }
    }