Error

"the trait Send is not implemented for (some async type)" — How to Fix

Async
2026-04-17T12:05:42+00:00
Fix the 'trait Send is not implemented' error by ensuring all struct fields are thread-safe or wrapping them in Arc and Mutex.

The error occurs because the type you are trying to send across threads does not implement the Send trait, which is required for thread-safe data transfer. To fix this, ensure all fields within your struct implement Send, or wrap non-Send types like Rc<T> in a Mutex or replace them with thread-safe alternatives like Arc<T>.

use std::sync::{Arc, Mutex};
use std::thread;

struct Data {
    // Replace Rc with Arc for thread safety
    counter: Arc<Mutex<usize>>,
}

fn main() {
    let data = Data {
        counter: Arc::new(Mutex::new(0)),
    };

    let handle = thread::spawn(move || {
        let mut num = data.counter.lock().unwrap();
        *num += 1;
    });

    handle.join().unwrap();
}