rust - 丢弃最后一个发件人但收信人仍处于事件状态时，是否可以在Tokio MPSC中保留项目？

Question

我的Tokio MPSC队列有限，只有一个发送者和一个接收者。我在一个任务中放入了几项(在本例中为1到10，包括1和10)，然后在另一项任务中将这些项拉出。如预期的那样，接收器处理所有10个值。
然后，我在处理之间添加了一些其他异步任务(在这种情况下，通过在接收循环中取消注释sleep调用)，现在，最后一个发送者完成时， channel 的内容将被丢弃。

use tokio::sync::mpsc;
use tokio::time::sleep;
use std::time::Duration;

#[tokio::main]
async fn main() {
    let (mut tx, mut rx) = mpsc::channel(3);
    
    tokio::spawn(async move {
        while let Some(val) = rx.recv().await {
            println!("Recieved {}", val);
            //sleep(Duration::from_secs(1)).await;
        }
        
        println!("Recieve finished");
    });
    
    for i in 1..=10i32 {
        tx.send(i).await.unwrap();
        println!("Sent {}", i);
    }
}

Rust Playground
这是注释掉 sleep的输出(交错值的顺序有时会更改，但始终会打印“已接收10”):

Sent 1
Recieved 1
Recieved 2
Sent 2
Sent 3
Recieved 3
Recieved 4
Sent 4
Sent 5
Recieved 5
Recieved 6
Sent 6
Sent 7
Recieved 7
Recieved 8
Sent 8
Sent 9
Recieved 9
Recieved 10
Sent 10

这是未注释 sleep的输出:

Sent 1
Sent 2
Sent 3
Recieved 1
Sent 4
Recieved 2
Sent 5
Recieved 3
Sent 6
Recieved 4
Sent 7
Recieved 5
Sent 8
Recieved 6
Sent 9
Recieved 7
Sent 10

是否有任何方法可以确定即使删除了最后一个 Reciever后(假设没有删除 Sender)， Reciever也处理了放入队列中的所有值？ close函数似乎可以做到这一点，但是却是另一种方式(确保在删除 Reciever之前已处理了队列内容)。如果没有，是否存在可以提供此保证的备用异步友好MPSC实现？

Answer 1

如注释中所述，问题是您的程序在接收器线程完成之前退出。只需确保退出之前先等待即可:

use tokio::sync::mpsc;
use tokio::time::sleep;
use std::time::Duration;

#[tokio::main]
async fn main() {
    let (mut tx, mut rx) = mpsc::channel(3);
    
    let join_handle = tokio::spawn(async move {
        while let Some(val) = rx.recv().await {
            println!("Received {}", val);
            //sleep(Duration::from_secs(1)).await;
        }
        
        println!("Receive finished");
    });
    
    for i in 1..=10i32 {
        tx.send(i).await.unwrap();
        println!("Sent {}", i);
    }
    
    std::mem::drop(tx); // Drop the sender so the receiver doesn't listen forever
    join_handle.await.unwrap(); // Wait for the receiver to finish processing
}

Sent 1
Received 1
Received 2
Sent 2
Sent 3
Sent 4
Sent 5
Received 3
Received 4
Received 5
Sent 6
Sent 7
Sent 8
Received 6
Received 7
Received 8
Sent 9
Sent 10
Received 9
Received 10
Receive finished