bus: Receivers don't always get the broadcasted item

Took me all day but I finally got a simple test case. If you cargo run this a few times it will eventually hang (on my machine anyway).

extern crate bus;

use std::thread;

use bus::Bus;

fn main() {
    println!("Starting");

    let strings = vec!["hi", "bye", "one", "two"];
    let mut bus = Bus::new(2);

    {
        let recv = bus.add_rx();

        thread::spawn(move || {
            println!("Looping 1");
            for rec in recv {
                println!("Got 1 :: {}", rec);
            }
        });
    };

    {
        let recv = bus.add_rx();

        thread::spawn(move || {
            println!("Looping 2");
            for rec in recv {
                println!("Got a 2 :: {}", rec);
            }
        });
    };

    for f in strings {
        println!("bcast :: {}", f);
        bus.broadcast(0);
    }
    println!("Done");
}

Example output

Finishes:

    Finished dev [unoptimized + debuginfo] target(s) in 0.08s
     Running `target/debug/fse_dump`
Starting
Looping 1
bcast :: hi
bcast :: bye
Looping 2
Got 1 :: 0
bcast :: one
Got 1 :: 0
Got 1 :: 0
Got a 2 :: 0
Got a 2 :: 0
Got a 2 :: 0
bcast :: two
Got 1 :: 0
Got a 2 :: 0
Done

Stuck:

    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target/debug/fse_dump`
Starting
Looping 1
bcast :: hi
Looping 2
Got a 2 :: 0
bcast :: bye
bcast :: one
Got 1 :: 0
Got 1 :: 0
Got 1 :: 0
bcast :: two

Machine info:

$ uname -a
Darwin 34363bc7dc9c 18.2.0 Darwin Kernel Version 18.2.0: Thu Dec 20 20:46:53 PST 2018; root:xnu-4903.241.1~1/RELEASE_X86_64 x86_64 i386 MacBookPro11,3 Darwin

$ rustc --version
rustc 1.33.0 (2aa4c46cf 2019-02-28)