block-on: Add example from Chapter 20, Asynchronous Programming.
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/target/
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Cargo.lock
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[package]
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name = "block-on"
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version = "0.1.0"
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authors = ["You <you@example.com>"]
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edition = "2018"
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# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
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[dependencies]
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waker-fn = "1.1"
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futures-lite = "1.11"
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crossbeam = "0.8"
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[dev-dependencies]
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async-std = "1.7"
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use waker_fn::waker_fn; // Cargo.toml: waker-fn = "1.1"
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use futures_lite::pin; // Cargo.toml: futures-lite = "1.11"
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use crossbeam::sync::Parker; // Cargo.toml: crossbeam = "0.8"
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use std::future::Future;
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use std::task::{Context, Poll};
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pub fn block_on<F: Future>(future: F) -> F::Output {
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let parker = Parker::new();
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let unparker = parker.unparker().clone();
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let waker = waker_fn(move || unparker.unpark());
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let mut context = Context::from_waker(&waker);
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pin!(future);
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loop {
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match future.as_mut().poll(&mut context) {
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Poll::Ready(value) => return value,
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Poll::Pending => parker.park(),
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}
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}
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}
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#[test]
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fn test() {
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assert_eq!(block_on(std::future::ready(42)), 42);
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use async_std::task::{spawn, sleep};
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use futures_lite::FutureExt;
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use std::time::Duration;
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assert_eq!(
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block_on({
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let one_sec = async {
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sleep(Duration::from_secs(1)).await;
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43
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};
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let half_sec = async {
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sleep(Duration::from_millis(500)).await;
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44
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};
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spawn(one_sec.race(half_sec))
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}),
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44);
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}
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