Make downloads asyncronous

[Veetaha]

I failed to integrate this library into my application which natively uses async/await and tokio.
I simply cannot create a model, because I get

thread 'main' panicked at 'Cannot start a runtime from within a runtime.
This happens because a function (like `block_on`) attempted to block the current thread 

every time I try to create SentimentModel::new().
I may be a newbie in tokio, so I tried

let model = tokio::task::block_in_place(|| SentimentModel::new(Default::default())).unwrap();

But this didn't solve the problem.
Also doing this:

let model = tokio::task::spawn_blocking(|| SentimentModel::new(Default::default()).unwrap())
    .await.unwrap();

also doesn't work because Rust complaints about sending some internal std::rc::Rc between threads. Even wrapping it all with Arc<Mutex<SentimentModel>> doesn't help.
I am simply perplexed and don't know how to use this crate inside of async fns...

[guillaume-be]

Hello,

The dependencies download is asynchronous. The code is located at:

rust-bert/src/common/resources.rs

Line 182 in 60bffe6

pub async fn download_resource(resource: &Resource) -> failure::Fallible<&PathBuf> {

I believe the problem is that I declared a #[tokio::main] which would not allow you to do so in your main application.

I am pushing some changes to make the overall function synchronous and use a local runtime instead. As I do not have code available to reproduce the issue, could you please check-out the branch async_download and let me know if this solves the issue?

[Veetaha]

Sorry for not mentioning, basically the reproduction is:

use rust_bert::pipelines::sentiment::SentimentModel;

#[tokio::main]
async fn main() {
    let model = SentimentModel::new(Default::default()).unwrap();

    // or
    let model = tokio::task::block_in_place(|| SentimentModel::new(Default::default())).unwrap();

    // or the following which you cannot do due to rust complaining about sending Rc between threads
    let model = tokio::task::spawn_blocking(|| SentimentModel::new(Default::default()).unwrap())
        .await.unwrap();
}

It should produce the Cannot start a runtime from within a runtime, let me know if it doesn't!

[guillaume-be]

Hello,

The library is by design currently synchronous, because the download part of it is a minimal feature.
To run the code in an asynchronous environment, please spawn a blocking thread:

#[tokio::main]
async fn main() {
    task::spawn_blocking(move || { let model = SentimentModel::new(Default::default()).unwrap(); });
}