gistfile1.txt

pub struct Node {
    ...
}

pub type RsvgNode = Weak<Node>;

/* This one works */
#[no_mangle]
pub unsafe extern fn rsvg_node_ref (raw_node: *mut RsvgNode) -> *const RsvgNode {
    assert! (!raw_node.is_null ());
    let weak_node: &RsvgNode = & *raw_node;
    let node = weak_node.upgrade ().unwrap ();

    mem::forget (node.clone ());

    raw_node
}

/* This one doesn't work; doesn't remove a reference at all */
#[no_mangle]
pub extern fn rsvg_node_unref (raw_node: *mut RsvgNode) {
    assert! (!raw_node.is_null ());
    let weak_node: &RsvgNode = unsafe { &*raw_node };
    let node = weak_node.upgrade ().unwrap ();

    println! ("before unref: {}", Rc::strong_count (&node));
    mem::drop (node);

    if weak_node.upgrade ().is_none () {
        let _ = unsafe { Box::from_raw (raw_node) };
        println! ("dropping");
    } else {
        println! ("not dropping");
    }
}

    #[test]
    fn node_refs_and_unrefs () {
        let node = Rc::new (Node::new (...));

        let node_ptr = Box::into_raw (Box::new (Rc::downgrade (&node)));

        let weak_node: &RsvgNode = unsafe { &*node_ptr };

        unsafe { rsvg_node_ref (node_ptr); }
        assert_eq! (Rc::strong_count (&node), 2);

        unsafe { rsvg_node_unref (node_ptr); }
        assert_eq! (Rc::strong_count (&node), 1);    // <------ This assertion fails; 2 != 1

        unsafe { rsvg_node_unref (node_ptr); }
        assert! (weak_node.upgrade ().is_none ());
    }