Trc

Trc is a biased reference-counted smart pointer for Rust that allows for interior mutability. Trc<T> is a heap-allocated smart pointer for sharing data across threads is a thread-safe manner without putting locks on the data. Trc<T> stands for: Thread Reference Counted. Trc<T> provides a shared ownership of the data similar to Arc<T> and Rc<T>. It implements biased reference counting, which is based on the observation that most objects are only used by one thread. This means that two reference counts can be created: one for thread-local use, and one atomic one for sharing between threads. This implementation of biased reference counting sets the atomic reference count to the number of threads using the data.

A cycle between Trc pointers cannot be deallocated as the reference counts will never reach zero. The solution is a Weak<T>. A Weak<T> is a non-owning reference to the data held by a Trc<T>. They break reference cycles by adding a layer of indirection and act as an observer. They cannot even access the data directly, and must be converted back into Trc<T>. Weak<T> does not keep the value alive (whcih can be dropped), and only keeps the backing allocation alive.

To prevent name clashes, Weak<T>'s functions are associated.

Examples

Example of Trc<T> in a single thread:

use trc::Trc;

let mut trc = Trc::new(100);
assert_eq!(*trc, 100);
*trc = 200;
assert_eq!(*trc, 200);

Example of Trc<T> with multiple threads:

use std::thread;
use trc::Trc;

let trc = Trc::new(100);
let mut trc2 = Trc::clone_across_thread(&trc);

let handle = thread::spawn(move || {
    *trc2 = 200;
});

handle.join().unwrap();
assert_eq!(*trc, 200);

Example of Weak<T> in a single thread:

use trc::Trc;
use trc::Weak;

let trc = Trc::new(100);
let weak = Weak::from_trc(&trc);
let mut new_trc = Weak::to_trc(&weak).unwrap();
println!("Deref test! {}", *new_trc);
println!("DerefMut test");
*new_trc = 200;
println!("Deref test! {}", *new_trc);

Example of Weak<T> with multiple threads:

use std::thread;
use trc::Trc;
use trc::Weak;

let trc = Trc::new(100);
let weak = Weak::from_trc(&trc);

let handle = thread::spawn(move || {
    let mut trc = Weak::to_trc(&weak).unwrap();
    println!("{:?}", *trc);
    *trc = 200;
});
handle.join().unwrap();
println!("{}", *trc);
assert_eq!(*trc, 200);