some unexpected panic

[huangjj27]

hello world example is modified as follow:

# Cargo.toml
[package]
name = "async_runtime"
version = "0.1.0"
authors = ["huangjj27 <huangjj.27@qq.com>"]
edition = "2018"

[dependencies]
runtime = "0.3.0-alpha.3"
futures-preview = "0.3.0-alpha.15"

// main.rs
#![feature(async_await, await_macro)]

async fn say_hi(num: usize) {
    println!("Hello, async - {}!", num);
}

#[runtime::main]
async fn main() {
    for i in 1..=100 {
        runtime::spawn(async move {
            let i = i;
            say_hi(i).await;

            Ok::<(), std::io::Error>(())
        });
    }
}

then, run:

PS E:\learning-rust\async_runtime> cargo +nightly run
   Compiling async_runtime v0.1.0 (E:\learning-rust\async_runtime)
    Finished dev [unoptimized + debuginfo] target(s) in 3.16s
     Running `target\debug\async_runtime.exe`
Hello, async - 2!
Hello, async - 3!
Hello, async - 4!
Hello, async - 5!
Hello, async - 6!
Hello, async - 7!
Hello, async - 8!
Hello, async - 9!
Hello, async - 10!
Hello, async - 11!
Hello, async - 16!
Hello, async - 13!
Hello, async - 14!
Hello, async - 15!

and run again:

PS E:\learning-rust\async_runtime> cargo +nightly run
    Finished dev [unoptimized + debuginfo] target(s) in 0.27s
     Running `target\debug\async_runtime.exe`
Hello, async - 1!
Hello, async - 3!
thread 'thread 'thread 'Hello, async - 2!
thread '<unnamed>thread 'thread '<unnamed>thread '<unnamed><unnamed>' panicked at '<unnamed><unnamed>' panicked at '

Expected Behaviour

It should print 100 times with no specific order

[yoshuawuyts]

Thanks for opening this issue! Yeah, what's happening is that the .spawn call is not being awaited:

#![feature(async_await, await_macro)]

async fn say_hi(num: usize) {
    println!("Hello, async - {}!", num);
}

#[runtime::main]
async fn main() {
    for i in 1..=100 {
        runtime::spawn(async move {
            let i = i;
            say_hi(i).await;

            Ok::<(), std::io::Error>(())
        }).await;
    }
}

We should probably fix this by adding #[must_use] attributes throughout the code so it will become clearer that Futures aren't being awaited where appropriate.

However, this processes the list of futures in order. The way to create an unordered list of futures is by using futures::stream::FuturesUnordered:

#![feature(async_await, await_macro)]

use futures::stream::FuturesUnordered;
use futures::prelude::*;

async fn say_hi(num: usize) {
    println!("Hello, async - {}!", num);
}

#[runtime::main]
async fn main() {
    let mut collection = FuturesUnordered::new();
    for i in 1..=100 {
        let fut = runtime::spawn(async move {
            let i = i;
            say_hi(i).await;

            Ok::<(), std::io::Error>(())
        });
        collection.push(fut);
    }

    while let Some(_) = collection.next().await { }
}

This should hopefully solve your issue!

[yoshuawuyts]

Actually feeling pretty confident this issue should be solved. Going to go ahead and close it. I've filed #30 to address the structural problem.

If there's anything missing, I'd be happy to reopen this!

[huangjj27]

This should hopefully solve your issue!

@yoshuawuyts thanks! your reply help and teach me alot!