TcpListener locked until TcpStream is closed. How to handle connection on new thread and avoid blocking?

Question

EDIT: It is now solved, the problem was some kind of strange behaviour in Windows with the way I was using to connect to the server. Sorry :(

I am trying to write a simple TCP server in which each connection is processed in a new thread. The connection must be kept active for a long period of time, and while client's connections are being processed, new connections must be accepted and processed.

Here an example of the code I am running:

use std::net::{TcpListener, TcpStream};
use std::io::{Write, Read};

fn main() {
    let addr_str = format!("0.0.0.0:{}", 1234);
    if let Ok(tcp_listener) = std::net::TcpListener::bind(addr_str) {
        tcp_listener.set_nonblocking(true);
        println!("listening on 0.0.0.0:{}", 1234);
        for tcp_stream in tcp_listener.incoming() {
            if let Ok(mut tstream) = tcp_stream {
                tstream.set_nonblocking(true);
                println!("open connection!");
                std::thread::spawn(move|| {
                    std::thread::sleep(std::time::Duration::from_millis(10000)); // sleep to simulate the processing, but in the real server it cloud be a really long task.. probably hours..
                    tstream.write(b"hello world:)");
                    println!("client disconnected ...");
                });
            }
        }
    } else {
        println!("ERROR: unable to create TcpListener");
    }
}

The problem is it only accepts 2 connections at the same time, so no new connections are accepted and processed until one of the previously accepted connection is finished.

Please, could you tell me what I am doing wrong? Thank you very much!