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use std::pin::Pin;
use std::sync::{Arc, Mutex};
use futures::Future;
use futures::task::{Context, Poll};
pub struct CallbackFuture<T> {
loader: Option<Box<dyn FnOnce(Box<dyn FnOnce(T) + Send + 'static>) + Send + 'static>>,
result: Arc<Mutex<Option<T>>>,
}
impl<T> CallbackFuture<T> {
pub fn new(loader: impl FnOnce(Box<dyn FnOnce(T) + Send + 'static>) + Send + 'static)
-> CallbackFuture<T> {
CallbackFuture {
loader: Some(Box::new(loader)),
result: Arc::new(Mutex::new(None)),
}
}
pub fn ready(value: T) -> CallbackFuture<T> {
CallbackFuture {
loader: None,
result: Arc::new(Mutex::new(Some(value))),
}
}
}
impl<T: Send + 'static> Future for CallbackFuture<T> {
type Output = T;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let self_mut = self.get_mut();
match self_mut.loader.take() {
Some(loader) => {
let waker = cx.waker().clone();
let result = self_mut.result.clone();
loader(Box::new(move |value| {
*result.lock().unwrap() = Some(value);
waker.wake();
}));
Poll::Pending
}
None => {
match self_mut.result.lock().unwrap().take() {
Some(value) => Poll::Ready(value),
None => Poll::Pending,
}
}
}
}
}
#[cfg(test)]
mod tests {
use std::thread;
use std::time::Duration;
use futures::{executor::block_on, join};
use crate::CallbackFuture;
#[test]
fn test_complete_async() {
let fu = CallbackFuture::new(move |complete| {
thread::spawn(move || { complete(42); });
});
assert_eq!(block_on(fu), 42);
}
#[test]
fn test_complete_sync() {
let fu = CallbackFuture::new(move |complete| {
complete(42);
});
assert_eq!(block_on(fu), 42);
}
#[test]
fn test_ready() {
let fu = CallbackFuture::ready(42);
assert_eq!(block_on(fu), 42);
}
#[test]
fn test_join() {
let all = async {
let fu1 = CallbackFuture::new(move |complete| {
complete("Hello");
});
let fu2 = CallbackFuture::ready(", ");
let fu3 = CallbackFuture::new(move |complete| {
thread::spawn(move || { complete("world!"); });
});
let (r1, r2, r3) = join!(fu1, fu2, fu3);
[r1, r2, r3].concat()
};
assert_eq!(block_on(all), "Hello, world!");
}
#[test]
fn test_await() {
let all = async {
let r1 = CallbackFuture::new(move |complete| {
thread::sleep(Duration::from_millis(100));
complete("Hello");
}).await;
let r2 = CallbackFuture::ready(", ").await;
let r3 = CallbackFuture::new(move |complete| {
thread::spawn(move || { complete("world!"); });
}).await;
[r1, r2, r3].concat()
};
assert_eq!(block_on(all), "Hello, world!");
}
#[test]
fn test_async_fn() {
async fn do_async() -> String {
CallbackFuture::new(move |complete| {
thread::spawn(move || { complete("Hello, world!".to_string()); });
}).await
}
assert_eq!(block_on(do_async()), "Hello, world!");
}
}