Problems to parallel or thread an Actix_web Server

Question

I wish to resolve the following code, but Rust panics because the actix future server() does not implement the trait Send. I didn't find a way to paralelize the actix server whithout error.

use tokio::runtime::Runtime;
use actix_web::{get, App, HttpResponse, HttpServer, Responder};

fn main() {
    let rt = Runtime::new().unwrap();
    let handle = rt.spawn(server());
    rt.block_on(handle).unwrap();

    // other activities in paralell with the server, is a crypto bot
    // and the server is for view the behavior
}

#[get("/")]
async fn hello_world() -> impl Responder {
    HttpResponse::Ok().body("Hello world!")
}

async fn server() -> Result<(), std::io::Error> {
    HttpServer::new(|| {
        App::new().service(hello_world)
    })
    .bind(("127.0.0.1", 5000))?
    .run()
    .await
}

the relevant panic info is the following:

error: future cannot be sent between threads safely
   --> src/main.rs:7:27
    |
7   |     let handle = rt.spawn(server());
    |                           ^^^^^^^^ future returned by `server` is not `Send`
    |
    = help: within `impl std::future::Future<Output = Result<(), std::io::Error>>`, the trait `Send` is not implemented for `Rc<[Box<dyn Fn() -> Pin<Box<dyn Future<Output = ...>>>>]>`
note: future is not `Send` as this value is used across an await

T2345 · Accepted Answer · 2025-07-28 21:09:36Z

0

Use actix_web::rt::spawn(), which does not have a Send requirement, and runs the future on the current thread:

https://docs.rs/actix-web/latest/actix_web/rt/fn.spawn.html

Any other Send futures or tasks can be spawned into different threads, and any other non-Send (!Send) futures can be spawned on the same thread, they will cooperate to share execution time.

If you need a dedicated thread for a !Send future, you can create it manually using std::thread::Builder, then use Handle::block_on() to call actix_web::rt::spawn() to run the future locally on that thread.

Here is a similar answer that covers most of that:

https://stackoverflow.com/a/75387575/4970342

answered Jul 28 at 21:09

T2345

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