A sort of an Arc-RwLock combination..

That aims to be simple and straightforward to use when sharing data between threads.

An attempt at creating an Arc-RwLock combination that is straightforward to use and no hassle , instead of worrying about being fast and lean.

• cloning referefences works like Arc
• made for sharing objects between threads without worry
• locking things works like RwLock with write() or read()
• it spins a few times and then queues if a lock is not obtained
• miri seems to be happy , so i trust it doesnt leak too much memory etc.
• requires that everything you stick into it is Send+Sync
• no need to constantly .unwrap() things instead it will just block forever or blow up

Example

use cura::Cura;
trait Foo:Send+Sync
{
    fn get(&self)->i32;
    fn set(&mut self,i:i32);
}
#[derive(Debug)]
struct FF{i:i32,};
struct BB{i:i32};
//!
impl Foo for FF{
    fn get(&self)->i32{return self.i;}
    fn set(&mut self,i:i32){self.i=i;}
}
//!
impl Foo for BB{
    fn get(&self)->i32{return self.i;}
    fn set(&mut self,i:i32){self.i=i;}
}
//!
let t=FF{i:1};
//!
// you can do straight "from_box" but currently its impossible to
// "alter" unsized types
let foo2:Cura<dyn Foo>=Cura::from_box(Box::new(FF{i:2}));
let foo:Cura<Box<dyn Foo>>=Cura::new(Box::new(t));
let a=foo.clone();
let b=foo.clone();
//!
{
    assert_eq!(a.read().get(),1);
    {
        a.alter(|s|{
            s.set(2);
            Some(())
        });
    }
    {
        a.alter(|s|{ //this only works for Sized types
            *s=Box::new(BB{i:2});
            Some(())
        });
    }
    let lock=a.read();
    let v=lock;
    assert_eq!(v.get(),2)
}//lock dropped here
{
    (*b.write()).set(3); //lock dropped here i think 
}
//!
assert_eq!((*a.read()).get(),3);
//!