How to Use Marker Traits (Send, Sync, Unpin) in Rust

Type System
2026-04-17T12:05:42+00:00
Send, Sync, and Unpin are marker traits that define how custom types can be safely shared or moved across threads and async contexts in Rust.

You use Send, Sync, and Unpin as marker traits to tell the compiler how your custom types behave in concurrent or asynchronous contexts. Send allows a type to be transferred between threads, Sync allows a type to be shared between threads via references, and Unpin allows a type to be moved in memory after being pinned. You typically implement these automatically using #[derive] or explicitly for custom types that need specific safety guarantees.

use std::sync::Arc;
use std::thread;

// Automatically implements Send and Sync if all fields do
#[derive(Debug)]
struct MyData {
    value: i32,
}

fn main() {
    let data = Arc::new(MyData { value: 42 });
    let handle = thread::spawn(move || {
        println!("Data from thread: {}", data.value);
    });
    handle.join().unwrap();
}