#![feature(test)]

extern crate test;
use crate::test::Bencher;

use futures::executor::block_on;
use futures::future::Future;
use futures::task::{Context, Poll, Waker};
use std::pin::Pin;

#[bench]
fn thread_yield_single_thread_one_wait(b: &mut Bencher) {
    const NUM: usize = 10_000;

    struct Yield {
        rem: usize,
    }

    impl Future for Yield {
        type Output = ();

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            if self.rem == 0 {
                Poll::Ready(())
            } else {
                self.rem -= 1;
                cx.waker().wake_by_ref();
                Poll::Pending
            }
        }
    }

    b.iter(|| {
        let y = Yield { rem: NUM };
        block_on(y);
    });
}

#[bench]
fn thread_yield_single_thread_many_wait(b: &mut Bencher) {
    const NUM: usize = 10_000;

    struct Yield {
        rem: usize,
    }

    impl Future for Yield {
        type Output = ();

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            if self.rem == 0 {
                Poll::Ready(())
            } else {
                self.rem -= 1;
                cx.waker().wake_by_ref();
                Poll::Pending
            }
        }
    }

    b.iter(|| {
        for _ in 0..NUM {
            let y = Yield { rem: 1 };
            block_on(y);
        }
    });
}

#[bench]
fn thread_yield_multi_thread(b: &mut Bencher) {
    use std::sync::mpsc;
    use std::thread;

    const NUM: usize = 1_000;

    let (tx, rx) = mpsc::sync_channel::<Waker>(10_000);

    struct Yield {
        rem: usize,
        tx: mpsc::SyncSender<Waker>,
    }
    impl Unpin for Yield {}

    impl Future for Yield {
        type Output = ();

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            if self.rem == 0 {
                Poll::Ready(())
            } else {
                self.rem -= 1;
                self.tx.send(cx.waker().clone()).unwrap();
                Poll::Pending
            }
        }
    }

    thread::spawn(move || {
        while let Ok(task) = rx.recv() {
            task.wake();
        }
    });

    b.iter(move || {
        let y = Yield {
            rem: NUM,
            tx: tx.clone(),
        };

        block_on(y);
    });
}
