Show that threads work in parallel

• spawn will create a new thread. We can use thread::current().id() to get the id of the current thread.
• join in the main thread will block till the other thread stops.
• We can see "Loop in main thread ended" is already printed before the "Spawned thread ended", but then the main thread waits.

use std::thread;
use std::time::Duration;

fn main() {
    println!("Before starting: {:?}", thread::current().id());

    let handle = thread::spawn(|| {
        for i in 1..=10 {
            println!(
                "Hi number {} from the spawned thread! {:?}",
                i,
                thread::current().id()
            );
            thread::sleep(Duration::from_millis(1));
        }
        println!("Spawned thread ended");
    });

    //thread::sleep(Duration::from_millis(1));
    //thread::sleep(Duration::from_micros(1));
    for i in 1..=5 {
        println!(
            "Hi number {} from the main    thread! {:?}",
            i,
            thread::current().id()
        );
        thread::sleep(Duration::from_millis(1));
    }

    println!("Loop in main thread ended");
    handle.join().unwrap(); // waiting for the other thread to end.
    println!("After ending: {:?}", thread::current().id());

    println!("Exiting");
}

Before starting: ThreadId(1)
Hi number 1 from the main    thread! ThreadId(1)
Hi number 1 from the spawned thread! ThreadId(2)
Hi number 2 from the main    thread! ThreadId(1)
Hi number 2 from the spawned thread! ThreadId(2)
Hi number 3 from the main    thread! ThreadId(1)
Hi number 3 from the spawned thread! ThreadId(2)
Hi number 4 from the main    thread! ThreadId(1)
Hi number 4 from the spawned thread! ThreadId(2)
Loop in main thread ended
Hi number 5 from the spawned thread! ThreadId(2)
Hi number 6 from the spawned thread! ThreadId(2)
Hi number 7 from the spawned thread! ThreadId(2)
Hi number 8 from the spawned thread! ThreadId(2)
Hi number 9 from the spawned thread! ThreadId(2)
Spawned thread ended
After ending: ThreadId(1)
Exiting

• thread
• spawn
• sleep
• join
• current