An example of mpmc with flume crate

mpmc.rs

// This will spawn 2 producer threads which will try to keep up to NUM_SESSIONS Sessions available for consumers

use flume::Receiver;
use once_cell::sync::OnceCell;

#[derive(Debug, Clone)]
struct Session;

const NUM_SESSIONS: usize = 10;

static POOL: OnceCell<Receiver<Session>> = OnceCell::new();

fn get_session() -> Session {
    let pool = POOL.get_or_init(|| {
        let (tx, rx) = flume::bounded(NUM_SESSIONS);
        for _ in 0..2 {
            let tx = tx.clone();
            std::thread::spawn(move || loop {
                tx.send(Session).unwrap();
            });
        }
        rx
    });

    pool.recv().unwrap()
}

fn main() {
    let mut ses = 50;
    while ses > 0 {
        let _ = get_session();
        println!("Got session {}", ses);
        ses -= 1;
    }
}