Why does the newly created channel close？

[reison]

I have code a test, every thread create a channel, and asynchronous receiver message,look this:

fn test(res:Receiver){

let res = res.recv();

if res.is_err(){

    println!("{:?}",res.err().unwrap().to_string());

}

}

fn main() {

loop{

    std::thread::sleep(Duration::from_secs(1));

    std::thread::spawn(move ||{

        let (mut sender,mut res) = std::sync::mpsc::sync_channel(1);

        std::thread::spawn(move||{
            test(res);
        })
    });
}

}

the error message is:"receiving on a closed channel"
why every channel was closed when it created?I do not understand,someone konw?pls help, thanks!

[s3bk]

Because you are dropping the sender immediately.
If there is no sender remaining, the channel is closed.

[reison]

oh, u are right!thanks,so how could I make sender is alive？I think loop send like the heartbeat is bad idea?

[s3bk]

If you want to send a heartbeat, then the channel needs to be created outside of the loop.

Basically:

1. create channel
2. spawn thread that sends a message to the sender every second.
3. receive messages from the channel in the main thread

[reison]

I make one clone of sender with receiver to make sender alive as long as receiver, when receiver was drop, the sender was drop too, but it is a bad way?!