How to allow Child Process listen to TCP or Socket on RUST

Question

I am trying to write a service that listens to socket for local and port for remote request. However, when I fork new process, the child process cannot create tcpListener nor UnixListener. It gave me bad file descripor/failed to wake io driver error

process num: 0, pid: 51782 => cidr: 0.0.0.0:8000, socks: /tmp/srv/rust-uds-0.sock
process num: 1, pid: 51794 => cidr: 0.0.0.0:8001, socks: /tmp/src/rust-uds-1.sock
thread 'main' panicked at src/main.rs:109:57:
called `Result::unwrap()` on an `Err` value: Os { code: 9, kind: Uncategorized, message: "Bad file descriptor" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at /Users/xxxxx/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.34.0/src/runtime/io/driver.rs:209:27:
failed to wake I/O driver: Os { code: 9, kind: Uncategorized, message: "Bad file descriptor" }

In my code I have

#[tokio::main]
async fn main() {
    let args = Args::parse();

    //uses nix fork and just returns a proc index for printing
    let proc_idx = fork_service(args.numprocs).await;

    let tcp_cidr = format!("0.0.0.0:{}", args.port + proc_idx);
    let socket_path = format!("{}/rust-uds-{}.sock", socket_dir, proc_idx);
    println!("process idx: {}, pid: {} => cidr: {}, socks: {}", proc_idx, id(), tcp_cidr, socket_path);

    // build our application with a single route
    let app = Router::new()
    .route("/", get(index))
    .route("/healthcheck", get(healthcheck))
    .route("/delay/:seconds", get(delay));

    // process http request from remote machine
    let tcplistener = TcpListener::bind(tcp_cidr).await.unwrap();
    axum::serve(tcplistener, app).await.unwrap();
}

I am confused on why this would failed cuz the listener is created after the fork, so there are not sharing. If args.numproc == 1, then everything works perfectly. please help