How to await an async function in an async tauri command?

[shi-yan]

I wasn't able to find an example and the following doesn't compile:

#![cfg_attr(
    all(not(debug_assertions), target_os = "windows"),
    windows_subsystem = "windows"
)]

use std::sync::Mutex;

struct State {
    content: String
}

impl State {
    fn new() -> Self {
        State {
            content: "test".to_string()
        }
    }

    pub async fn test_async(&mut self) -> Result<String, String> {
        Ok("test".to_string())
    }
}

// Learn more about Tauri commands at https://tauri.app/v1/guides/features/command
#[tauri::command]
async fn greet(state: tauri::State<'_, Mutex< State>>,) -> Result<String, String> {
    //format!("Hello, {}! You've been greeted from Rust!", name)
    if let Ok(content) = state.lock().unwrap().test_async().await
    {
        return Ok(content.to_string());
    }
    else {
        return Err("test".to_string());
    }
}

fn main() {
    let state = Mutex::new(State::new());
    tauri::Builder::default()
    .manage(state)
        .invoke_handler(tauri::generate_handler![greet])
        .run(tauri::generate_context!())
        .expect("error while running tauri application");
}

the above gives:

error: future cannot be sent between threads safely
   --> src/main.rs:25:1
    |
25  | #[tauri::command]
    | ^^^^^^^^^^^^^^^^^ future returned by `greet` is not `Send`
...
42  |         .invoke_handler(tauri::generate_handler![greet])
    |                         ------------------------------- in this macro invocation
    |
    = help: within `impl Future<Output = Result<String, String>>`, the trait `Send` is not implemented for `MutexGuard<'_, State>`
note: future is not `Send` as this value is used across an await
   --> src/main.rs:29:50
    |
28  |     let mut state_inner = state.lock().unwrap();
    |         --------------- has type `MutexGuard<'_, State>` which is not `Send`
29  |     if let Ok(content) = state_inner.test_async().await
    |                                                  ^^^^^^ await occurs here, with `mut state_inner` maybe used later
...
36  | }
    | - `mut state_inner` is later dropped here
note: required by a bound in `ResultFutureTag::future`
   --> /Users/shiy/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-1.2.4/src/command.rs:289:42
    |
289 |       F: Future<Output = Result<T, E>> + Send,
    |                                          ^^^^ required by this bound in `ResultFutureTag::future`
    = note: this error originates in the macro `__cmd__greet` which comes from the expansion of the macro `tauri::generate_handler` (in Nightly builds, run with -Z macro-backtrace for more info)

I tried multiple ways, none worked, including using Arc<RwLock> for example, if Future is not send, I can't await another async function at all?

I also tried a synchronized workaround, using tauri's block_on, but that freezes the tauri ui.

[shi-yan]

I solved it by https://stackoverflow.com/questions/67277282/async-function-the-trait-stdmarkersend-is-not-implemented-for-stdsync

[ryardley]

Would love to see a code snippet to understand what you have done specifically.

[mehedimi]

@shi-yan Hay, could you please share some code snippets? I faced this error bellow

18 | /   async move {
19 | |     let data = Connection::find().all(state.setup.lock().unwrap().deref_mut()).await;
20 | |
21 | |     dbg!(data);
22 | |
23 | |     Ok(())
24 | |   }.boxed();
   | |    -^^^^^ method not found in `[async block@src/connection_commands.rs:18:3: 24:4]`
   | |____|