foo.rs

#![feature(scoped)]
use std::thread;
use std::sync::mpsc::{channel, Sender, Receiver};

fn main() {
    let (tx1, rx1) = channel();
    let (tx2, rx2) = channel();
    let _b1 = Bomb1(tx1, rx2);
    let b = Box::new(4);
    foo(tx2, rx1, &b);
}

fn foo(done: Sender<()>, start: Receiver<()>, val: &i32) {
    let _t = thread::scoped(move || {
        drop(start.recv());
        println!("value at {:p} = {}", val, val);
        drop(done.send(()));
    });
    let _b2 = Bomb2;
}

struct Bomb1(Sender<()>, Receiver<()>);
impl Drop for Bomb1 {
    fn drop(&mut self) {
        println!("letting the child go");
        drop(self.0.send(()));
        drop(self.1.recv());
        println!("returning from main thread");
    }
}

struct Bomb2;
impl Drop for Bomb2 {
    fn drop(&mut self) {
        panic!("panicking on main thread");
    }
}