async-io 0.1.11

Async I/O and timers
Documentation 
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//! A simple `block_on()` that uses `async_io::parking` to wait for the next wakeup.
//!
//! Run with:
//!
//! ```
//! cargo run --example block_on
//! ```

use std::future::Future;
use std::task::{Context, Poll};

use async_io::parking;
use futures_lite::pin;
use waker_fn::waker_fn;

fn block_on<T>(future: impl Future<Output = T>) -> T {
    let (p, u) = parking::pair();
    let waker = waker_fn(move || u.unpark());
    let cx = &mut Context::from_waker(&waker);

    pin!(future);
    loop {
        match future.as_mut().poll(cx) {
            Poll::Ready(t) => return t,
            Poll::Pending => p.park(),
        }
    }
}

fn main() {
    block_on(async {
        println!("Hello world!");
    })
}