在发送消息之前，oneshot关闭

Question

我想使用oneshot在两个任务之间发送消息，但是不幸的是，发送方is_closed()在发送数据之前返回true。

同时，我在#L38发送oneshot::sender并在#L40接收消息发送者，在#L61发送消息，但是is_closed()方法返回它已关闭。

use futures::future::{Future, TryFutureExt};
use std::{
    pin::Pin,
    task::{Context, Poll},
};

use tokio::{
    io::{AsyncWrite, AsyncWriteExt},
    sync::{mpsc, oneshot},
};

use std::io::{Error, ErrorKind};

macro_rules! pin_mut {
    ($($x:ident),*) => { $(
        let mut $x = $x;
        #[allow(unused_mut)]
        let mut $x = unsafe {
            Pin::new_unchecked(&mut $x)
        };
    )* }
}

struct UdpStream {
    writer: mpsc::Sender<oneshot::Sender<usize>>,
}

impl AsyncWrite for UdpStream {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context,
        _buf: &[u8],
    ) -> Poll<std::io::Result<usize>> {
        let (tx, rx) = oneshot::channel::<usize>();
        let mut writer = self.writer.clone();

        let future = writer
            .send(tx)
            .map_err(|_| Error::new(ErrorKind::Other, "oh no!"))
            .and_then(|_| rx.map_err(|_| Error::new(ErrorKind::Other, "oh no!")));

        pin_mut!(future);
        future.poll(cx).map(|len| len)
    }
    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<std::io::Result<()>> {
        Poll::Ready(Ok(()))
    }
    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<std::io::Result<()>> {
        Poll::Ready(Ok(()))
    }
}

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let (tx, mut rx) = mpsc::channel::<oneshot::Sender<usize>>(10);
    let mut x = UdpStream { writer: tx };

    tokio::spawn(async move {
        let oneshot_sender = rx.recv().await.unwrap();
        dbg!(oneshot_sender.is_closed());
        oneshot_sender.send(123).unwrap();
    });

    let x = x.write("Hey".as_bytes()).await.unwrap();
    dbg!(x);

    Ok(())
}

$cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `target/debug/problem`
[src/main.rs:60] oneshot_sender.is_closed() = true
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: 123', src/libcore/result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

我创建了一个展示问题的存储库： https : //github.com/SajjadPourali/oneshot_sender-is_closed/

我在users.rust-lang中询问过，但是答案还没有太大帮助。