How to solve this lifetime problem?

help
#1

:sob: can someone help me with this? I've met this problem a lot of times.

    //in lib
    pub async fn run(&'static self, addr: String) -> Result<(), Box<dyn Error>> {
        let listener = TcpListener::bind("127.0.0.1:8080").await?;
        loop {
            let (socket, _) = listener.accept().await?;
            tokio::spawn(handle_connection(&self, socket));
        }
    }

//in main
App::new().run("".to_string());
// complains 
//temporary value dropped while borrowed 
//creates a temporary which is freed while still in use
#2

Why do you need the 'static lifetime for self? That tells the compiler self needs to be valid beyond the end of main, which is causing your compile error.

1 Like
#3

Hi, I try not using static but in the handle function would complains, and I don't want to copy the app each time in the loop.

#4

Consider passing around Arc<App> instead of &App.

pub async fn run(self: Arc<Self>, addr: String) -> Result<(), Box<dyn Error>> {
    let listener = TcpListener::bind("127.0.0.1:8080").await?;
    loop {
        let app = self.clone();
        let (socket, _) = listener.accept().await?;
        tokio::spawn(handle_connection(app, socket));
    }
}

in main:

//in main
Arc::new(App::new()).run("".to_string());

(You'll probably also need to change handle_connection to take Arc.)

Cloning the Arc is cheap, like copying a reference. The new Arc will still point to the same, shared App value.

#5

Hi, I tried your advice and I can complie, the only problem is when i run it, I get a stack overflow :joy:

#6

When the compiler tells you to add 'static don't listen to it. It's almost always a wrong, misleading suggestion.

When compiler says it wants 'static, it tries to say that all temporary references are forbidden. 'static just happens to be the only case of a reference that isn't temporary, but in practice it's a useless solution, because almost nothing in real programs can be static (i.e. a constant or leaked memory). The real solution is to use self-contained/owned types, Arc, or a copy of the data instead.

Compiler bug:

4 Likes
#7

Thank you!

#8

I was long annoyed by that suggestion, thanks for bringing it up! (it's only now that I see the issue on GitHub.)

#9

Any potential recursion or really big arrays in your code?

#10

yes it's my fault, I arranged a very big array in my code which causes the problem