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    use crate::runtime::task::RawTask;

    use std::fmt;
    use std::future::Future;
    use std::marker::PhantomData;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    cfg_rt! {
        /// An owned permission to join on a task (await its termination).
        ///
        /// This can be thought of as the equivalent of [`std::thread::JoinHandle`] for
        /// a task rather than a thread.
        ///
        /// A `JoinHandle` *detaches* the associated task when it is dropped, which
        /// means that there is no longer any handle to the task, and no way to `join`
        /// on it.
        ///
        /// This `struct` is created by the [`task::spawn`] and [`task::spawn_blocking`]
        /// functions.
        ///
        /// # Examples
        ///
        /// Creation from [`task::spawn`]:
        ///
        /// ```
        /// use tokio::task;
        ///
        /// # async fn doc() {
        /// let join_handle: task::JoinHandle<_> = task::spawn(async {
        ///     // some work here
        /// });
        /// # }
        /// ```
        ///
        /// Creation from [`task::spawn_blocking`]:
        ///
        /// ```
        /// use tokio::task;
        ///
        /// # async fn doc() {
        /// let join_handle: task::JoinHandle<_> = task::spawn_blocking(|| {
        ///     // some blocking work here
        /// });
        /// # }
        /// ```
        ///
        /// The generic parameter `T` in `JoinHandle<T>` is the return type of the spawned task.
        /// If the return value is an i32, the join handle has type `JoinHandle<i32>`:
        ///
        /// ```
        /// use tokio::task;
        ///
        /// # async fn doc() {
        /// let join_handle: task::JoinHandle<i32> = task::spawn(async {
        ///     5 + 3
        /// });
        /// # }
        ///
        /// ```
        ///
        /// If the task does not have a return value, the join handle has type `JoinHandle<()>`:
        ///
        /// ```
        /// use tokio::task;
        ///
        /// # async fn doc() {
        /// let join_handle: task::JoinHandle<()> = task::spawn(async {
        ///     println!("I return nothing.");
        /// });
        /// # }
        /// ```
        ///
        /// Note that `handle.await` doesn't give you the return type directly. It is wrapped in a
        /// `Result` because panics in the spawned task are caught by Tokio. The `?` operator has
        /// to be double chained to extract the returned value:
        ///
        /// ```
        /// use tokio::task;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        ///         Ok(5 + 3)
        ///     });
        ///
        ///     let result = join_handle.await??;
        ///     assert_eq!(result, 8);
        ///     Ok(())
        /// }
        /// ```
        ///
        /// If the task panics, the error is a [`JoinError`] that contains the panic:
        ///
        /// ```
        /// use tokio::task;
        /// use std::io;
        /// use std::panic;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        ///         panic!("boom");
        ///     });
        ///
        ///     let err = join_handle.await.unwrap_err();
        ///     assert!(err.is_panic());
        ///     Ok(())
        /// }
        ///
        /// ```
        /// Child being detached and outliving its parent:
        ///
        /// ```no_run
        /// use tokio::task;
        /// use tokio::time;
        /// use std::time::Duration;
        ///
        /// # #[tokio::main] async fn main() {
        /// let original_task = task::spawn(async {
        ///     let _detached_task = task::spawn(async {
        ///         // Here we sleep to make sure that the first task returns before.
        ///         time::sleep(Duration::from_millis(10)).await;
        ///         // This will be called, even though the JoinHandle is dropped.
        ///         println!("♫ Still alive ♫");
        ///     });
        /// });
        ///
        /// original_task.await.expect("The task being joined has panicked");
        /// println!("Original task is joined.");
        ///
        /// // We make sure that the new task has time to run, before the main
        /// // task returns.
        ///
        /// time::sleep(Duration::from_millis(1000)).await;
        /// # }
        /// ```
        ///
        /// [`task::spawn`]: crate::task::spawn()
        /// [`task::spawn_blocking`]: crate::task::spawn_blocking
        /// [`std::thread::JoinHandle`]: std::thread::JoinHandle
        /// [`JoinError`]: crate::task::JoinError
        pub struct JoinHandle<T> {
            raw: Option<RawTask>,
            _p: PhantomData<T>,
        }
    }

    unsafe impl<T: Send> Send for JoinHandle<T> {}
    unsafe impl<T: Send> Sync for JoinHandle<T> {}

    impl<T> JoinHandle<T> {
        pub(super) fn new(raw: RawTask) -> JoinHandle<T> {
            JoinHandle {
                raw: Some(raw),
                _p: PhantomData,
            }
        }

        /// Abort the task associated with the handle.
        ///
        /// Awaiting a cancelled task might complete as usual if the task was
        /// already completed at the time it was cancelled, but most likely it
        /// will complete with a `Err(JoinError::Cancelled)`.
        ///
        /// ```rust
        /// use tokio::time;
        ///
        /// #[tokio::main]
        /// async fn main() {
        ///    let mut handles = Vec::new();
        ///
        ///    handles.push(tokio::spawn(async {
        ///       time::sleep(time::Duration::from_secs(10)).await;
        ///       true
        ///    }));
        ///
        ///    handles.push(tokio::spawn(async {
        ///       time::sleep(time::Duration::from_secs(10)).await;
        ///       false
        ///    }));
        ///
        ///    for handle in &handles {
        ///        handle.abort();
        ///    }
        ///
        ///    for handle in handles {
        ///        assert!(handle.await.unwrap_err().is_cancelled());
        ///    }
        /// }
        /// ```
        pub fn abort(&self) {
            if let Some(raw) = self.raw {
                raw.shutdown();
            }
        }
    }

    impl<T> Unpin for JoinHandle<T> {}

    impl<T> Future for JoinHandle<T> {
        type Output = super::Result<T>;

        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            let mut ret = Poll::Pending;

            // Keep track of task budget
            let coop = ready!(crate::coop::poll_proceed(cx));

            // Raw should always be set. If it is not, this is due to polling after
            // completion
            let raw = self
                .raw
                .as_ref()
                .expect("polling after `JoinHandle` already completed");

            // Try to read the task output. If the task is not yet complete, the
            // waker is stored and is notified once the task does complete.
            //
            // The function must go via the vtable, which requires erasing generic
            // types. To do this, the function "return" is placed on the stack
            // **before** calling the function and is passed into the function using
            // `*mut ()`.
            //
            // Safety:
            //
            // The type of `T` must match the task's output type.
            unsafe {
                raw.try_read_output(&mut ret as *mut _ as *mut (), cx.waker());
            }

            if ret.is_ready() {
                coop.made_progress();
            }

            ret
        }
    }

    impl<T> Drop for JoinHandle<T> {
        fn drop(&mut self) {
            if let Some(raw) = self.raw.take() {
                if raw.header().state.drop_join_handle_fast().is_ok() {
                    return;
                }

                raw.drop_join_handle_slow();
            }
        }
    }

    impl<T> fmt::Debug for JoinHandle<T>
    where
        T: fmt::Debug,
    {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt.debug_struct("JoinHandle").finish()
        }
    }