Eddie's Blog

[Day5] Read Rust Atomics and Locks

by Mara Bos

At Topics: Chapter 1. Basics of Rust Concurrency

Prerequisites

  • Understand smart pointers

Notes

  • Any data shared between threads will need to live as long as the longest living thread.

  • A static item is never droped and has already exists before the main function of the program even starts.

    static X: [i32; 3] = [1, 2, 3];

thread::spawn(|| dbg!(&X)); // [src/main.rs:6] &X = [ 1, 2, 3,]

  • Some ways to share ownership to threads: static, Box::leak(Box::new([1, 2, 3]));, Arc

  • References are Copy, meaning that when you "move" them, the original still exists, just like with an integer or boolean.

Reference Counting

// reference counted
use std::rc::Rc;

// Both 'a' and 'b' Rc will refer to the same allocation; they share ownership.
let a = Rc::new([1, 2, 3]);
let b = a.clone();

assert_eq!(a.as_ptr(), b.as_ptr()); // Same allocation!
  • Threads use std::sync::Arc instead of std::rc::Rc while it guarantees that modifications to the reference counter are indivisible atomic operations

References