tokio_global_shared_state_example.rs

/*
[dependencies]
futures = "0.3"
tokio = { version = "1", features = ["full"] }
rand = "0.8"
 */

use std::sync::Arc;
use rand::prelude::*;

type AppResult<T> = Result<T, Box<dyn std::error::Error + Send + Sync + 'static>>;
type DataRef = Arc<Vec<&'static str>>;
type StateRef = Arc<dyn State + Send + Sync>;

trait State {
    fn data(&self) -> DataRef;
}

struct AppState {
    data: DataRef
}

impl State for AppState {
    fn data(&self) -> DataRef {
        Arc::clone(&self.data)
    }
}

async fn process(context: StateRef) -> AppResult<()> {
    let n = thread_rng().gen_range(0..=2);
    println!("{}", context.data()[n]);
    Ok(())
}

#[tokio::main]
async fn main() {
    let context = Arc::new(
        AppState {
        data: Arc::new(vec!["foo", "bar", "baz"]),
    }) as StateRef;

    let ha = tokio::spawn(process(Arc::clone(&context)));
    let hb = tokio::spawn(process(Arc::clone(&context)));
    let hc = tokio::spawn(process(Arc::clone(&context)));
    let _ = futures::join!(ha, hb, hc);
}