What is the difference between join and select in async

The terms join and select do not exist as keywords in Rust's async system; join is a method on JoinHandle to wait for a thread, while select is a macro in the tokio crate to wait for the first of multiple futures to complete. Use join to wait for a specific task to finish and select to handle multiple concurrent tasks where you only need the first result.

use tokio::select;
use std::time::Duration;

async fn main() {
    let handle = tokio::spawn(async { println!("Task done"); });
    
    select! {
        _ = tokio::time::sleep(Duration::from_secs(1)) => println!("Timeout"),
        _ = handle => println!("Task finished first"),
    }
    
    handle.await.unwrap();
}

Note: join is standard library (std::thread::JoinHandle), while select requires an external crate like tokio.

Think of join as waiting for a specific person to finish their task before you move on, ensuring that specific job is done. select is like standing at a crossroads waiting for the first of several people to arrive, so you can react immediately to whichever one gets there first. You use join when order matters and select when speed or the first available result matters.