pub struct Queue
{
    data: std::collections::VecDeque<u8>,
}

impl Queue
{
    pub fn push(&mut self, val: u8)
    {
        self.data.push_back(val);
    }

    pub fn pop(&mut self)
    {
        if !self.data.is_empty()
        {
            self.data.pop_front();
        }
    }

    pub fn front(&self) -> u8
    {
        *self.data.front().unwrap()
    }
}

fn processing(i_b: &mut Arc<RefCell<Queue>>, o_b: &mut Arc<RefCell<Queue>>)
    {
        i_b.get_mut().pop();
        print!("{}, {} : ", i_b.get_mut().front(), o_b.get_mut().front());
    }

error[E0277]: `std::cell::RefCell<Queue>` cannot be shared between threads safely
  --> srcmain.rs:69:14
   |
69 |     let _c = thread::spawn(move || {
   |              ^^^^^^^^^^^^^ `std::cell::RefCell<Queue>` cannot be shared between threads safely
   |
   = help: the trait `std::marker::Sync` is not implemented for `std::cell::RefCell<Queue>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::sync::Arc<std::cell::RefCell<Queue>>`
   = note: required because it appears within the type `[closure@srcmain.rs:69:28: 71:6 _a:std::sync::Arc<std::cell::RefCell<Queue>>, _b:std::sync::Arc<std::cell::RefCell<Queue>>]`
   = note: required by `std::thread::spawn`