use std::sync::Arc;
use std::sync::RwLock;
use std::os::raw::c_void;

struct Counter {
    val: u32,
}

impl Counter {
    fn inc(&mut self, n: &mut N) {
        self.val += n.val;
        n.val += 1;
    }
}

struct N {
    val: u32,
}

struct X {
    n: N,
    ctr: Counter,
}

fn main() {}

fn f(x_ptr: *mut c_void) {
    let x_ref = unsafe { &mut *(x_ptr as *mut Arc<RwLock<X>>) };
    let mut x_writer = x_ref.write().unwrap();
    x_writer.ctr.inc(&mut x_writer.n);
}