Exclude Send + Sync from async

hydroper1 · November 23, 2023, 11:57am

Using this macro causes the surrounding asynchronous context to implement !Send. I used it in my cross-platform timer API and I like to ensure everything is non concurrent.

/// Marks asynchronous code as `!Send`.
#[allow(unused)]
pub(crate) macro no_send {
    () => {
        futures::future::ready(std::marker::PhantomData::<*const ()>::default()).await;
    },
}

I'm in inertia with my Agera SDK project, but I'm wondering if I can implement !Sync to the surrounding async?

kpreid · November 23, 2023, 3:17pm

Does Sync ever matter? You can't access any part of an opaque Future through a & reference.

alice · November 23, 2023, 4:53pm

You can use a test like the following to ensure that Send and Sync have the value you want:

github.com

tokio-rs/tokio/blob/master/tokio/tests/async_send_sync.rs

#![warn(rust_2018_idioms)]
#![cfg(feature = "full")]
#![allow(clippy::type_complexity, clippy::diverging_sub_expression)]

use std::cell::Cell;
use std::future::Future;
use std::io::SeekFrom;
use std::net::SocketAddr;
use std::pin::Pin;
use std::rc::Rc;
use tokio::net::TcpStream;
use tokio::time::{Duration, Instant};

// The names of these structs behaves better when sorted.
// Send: Yes, Sync: Yes
#[derive(Clone)]
struct YY {}

// Send: Yes, Sync: No
#[derive(Clone)]

This file has been truncated. show original

system · February 21, 2024, 4:54pm

This topic was automatically closed 90 days after the last reply. We invite you to open a new topic if you have further questions or comments.

Topic		Replies	Views
Async, tokio & future code review	7	582	January 7, 2023
Await occurs here with maybe used later when combine tokio mutex with std mutex help	2	1443	November 2, 2022
Omit sync requirements	11	464	October 22, 2022
Send + Sync error help	7	147	March 22, 2024
Help, future is not 'Send', how to fix	3	1082	November 3, 2021

Exclude Send + Sync from async

Related Topics