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use tokio::sync::oneshot;
use std::cell::RefCell;
use std::collections::VecDeque;
use std::future::Future;
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};
thread_local! {
static QUEUE: RefCell<VecDeque<Box<dyn FnOnce() + Send>>> = RefCell::new(VecDeque::new())
}
#[derive(Debug)]
pub(crate) struct Blocking<T> {
rx: oneshot::Receiver<T>,
}
pub(crate) fn run<F, R>(f: F) -> Blocking<R>
where
F: FnOnce() -> R + Send + 'static,
R: Send + 'static,
{
let (tx, rx) = oneshot::channel();
let task = Box::new(move || {
let _ = tx.send(f());
});
QUEUE.with(|cell| cell.borrow_mut().push_back(task));
Blocking { rx }
}
impl<T> Future for Blocking<T> {
type Output = Result<T, io::Error>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
use std::task::Poll::*;
match Pin::new(&mut self.rx).poll(cx) {
Ready(Ok(v)) => Ready(Ok(v)),
Ready(Err(e)) => panic!("error = {:?}", e),
Pending => Pending,
}
}
}
pub(crate) async fn asyncify<F, T>(f: F) -> io::Result<T>
where
F: FnOnce() -> io::Result<T> + Send + 'static,
T: Send + 'static,
{
run(f).await?
}
pub(crate) fn len() -> usize {
QUEUE.with(|cell| cell.borrow().len())
}
pub(crate) fn run_one() {
let task = QUEUE
.with(|cell| cell.borrow_mut().pop_front())
.expect("expected task to run, but none ready");
task();
}
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