Requirement of async main function

[Raphiiko]

Hi there, I've been working on migrating my application to Tauri v2, and have been running into some difficulty specifically with migrating this plugin.

It seems that in c4b5ca3, the usage of tauri::async_runtime was swapped out, from which point on this plugin requires the application's main function to be made async and annotated with #[tokio::main].

As the application I am migrating blocks on async code in its setup function, this seems to cause some issues.

The recommended way to run async code in Tauri's setup function, seems to be as follows:

fn main() {
    tauri::Builder::default()
        .plugin(tauri_plugin_aptabase::Builder::new("<YOUR_APP_KEY>").build())
        .setup(|app| {
            tauri::async_runtime::block_on(async {
                // Run your async setup code
            });
            Ok(())
        })
        .invoke_handler(tauri::generate_handler![])
        .run(tauri::generate_context!())
        .expect("error while running tauri application");
}

However, as this example stands, the aptabase plugin will not initialize:

thread 'main' panicked at src\main.rs:44:31:
there is no reactor running, must be called from the context of a Tokio 1.x runtime

This is because the main function now has to be made async:

#[tokio::main]
async fn run() {
  ...

This is where my problem starts: Because the main function is now async, I can no longer seem to block on the async code in the setup handler:

Cannot start a runtime from within a runtime. This happens because a function (like `block_on`) attempted to block the current thread while the thread is being used to drive asynchronous tasks.       

Honestly, I'm quite stumped on how to solve this problem. My application relies on this async code as part of its setup, and as it stands I am stuck on an earlier commit and cannot migrate to the latest version of this plugin. I'm sure this change was made for a reason, but as no other first party Tauri plugin seems to require an async main function I cannot quite put my finger on why.

Any advice on how I could tackle this? Thank you!

[nekename]

Hey @Raphiiko

Could you try swapping out tauri::async_runtime::block_on for futures::executor::block_on in your code? Like in the commit you linked to. Never mind, see my comment below

I think this error occurs when both Tauri's asking runtime and direct usage of Tokio are used. My app, for example, is a lot of my own Rust and has minimal usage of Tauri APIs, so I use Tokio directly, I think that's why I would have made that change. I didn't know it would affect the other way around.

[nekename]

Ahh, I've found the answer. Could you try this?

#[tokio::main]
async fn main() {
    tauri::async_runtime::set(tokio::runtime::Handle::current());

    // ...
}

[Raphiiko]

Hi, thanks for looking into this. I've tried your suggestion on a freshly generated Tauri v2 application, however I'm running into the same issue:

Result

thread 'main' panicked at C:\Users\Raph\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\tauri-2.5.1\src\async_runtime.rs:208:27:
Cannot start a runtime from within a runtime. This happens because a function (like `block_on`) attempted to block the current thread while the thread is being used to drive asynchronous tasks.

Cargo.toml

[dependencies]
...
tauri-plugin-aptabase = { git = "https://github.com/aptabase/tauri-plugin-aptabase" }
tokio = { version = "1.44.2", features = ["full"] }

main.rs

#[tokio::main]
async fn main() {
    tauri::async_runtime::set(tokio::runtime::Handle::current());
    tauri::Builder::default()
        .plugin(tauri_plugin_aptabase::Builder::new("<APTABASE_TOKEN>").build())
        .setup(|app| {
            tauri::async_runtime::block_on(async {
                // Run your async setup code
            });
            Ok(())
        })
        .run(tauri::generate_context!())
        .expect("error while running tauri application");
}

[Raphiiko]

@nekename Your earlier suggestion to use futures::executor::block_on instead of
tauri::async_runtime::block_on does seem to fix the example, thank you!

For my full application it seems I had to swap out out every use of tauri::async_runtime::block_on for the futures equivalent for it to run, even those outside the setup function.

As my application already depends on the futures crate this isn't really an issue in my particular case, however considering this plugin isn't a generic Rust crate and specifically targeted for use with Tauri, would it not make more sense to depend on the tools provided by Tauri, rather than those coming from another 3rd party dependency?

Regardless, thanks for the help! (feel free to close this)

[nekename]

I'll have a look at some point, but if my suggestion didn't work then I'm not sure how to reconcile apps that use an async main function with Tauri's async runtime