Concurrency Traits

Thread safety traits

Send Trait

use std::thread;
use std::sync::Arc;
use std::rc::Rc;

fn main() {
    // Send = safe to SEND to another thread
    // Ownership can be transferred across thread boundaries

    // Owned data is Send if type is Send
    let data = vec![1, 2, 3, 4, 5];

    let handle = thread::spawn(move || {
        // data is moved here
        println!("Vec in thread: {:?}", data);
    });

    handle.join().unwrap();

    // Arc is Send (when T: Send + Sync)
    let shared = Arc::new(String::from("shared"));
    let shared_clone = Arc::clone(&shared);

    thread::spawn(move || {
        println!("Arc in thread: {}", shared_clone);
    }).join().unwrap();

    // Rc is NOT Send
    let rc = Rc::new(42);
    // thread::spawn(move || { println!("{}", rc); });  // Error!
    println!("\nRc must stay single-threaded: {}", rc);

    println!("\n=== Send Types ===");
    println!("- i32, String, Vec<T> where T: Send");
    println!("- Arc<T> where T: Send + Sync");
    println!("- Mutex<T> where T: Send");
    println!("- mpsc::Sender<T> where T: Send");

    println!("\n=== NOT Send ===");
    println!("- Rc<T>: non-atomic refcount");
    println!("- Raw pointers: *const T, *mut T");
    println!("- MutexGuard: must unlock in same thread");
}