Error Help: Type inside async block must be known in this context

[dogou77]

Hello, I am somewhat of an amateur when it comes to Rust (especially asynchronous programming in it). I am trying to find out a way to see if a task I spawned is still running after a loop so that I can cancel it. The only solution that made sense to me at my skill level was to make a Vector that holds all of the spawned tasks, and then check the vector to see if the tasks are still running. But this led to a bizarre problem that I cannot find a solution for anywhere. I have the following code that is giving me an error:

let mut tag_log_tasks = Vec::new();

The error goes as follows:

Error[E0698]: type inside `async` block must be known in this context
    --> src/main.rs:100:29
     |
100  |     let mut tag_log_tasks = Vec::new();
     |                             ^^^^^^^^ cannot infer type for type parameter `T` declared on the struct `Vec`
     |
note: the type is part of the `async` block because of this `await`
    --> src/main.rs:1006:139
     |
1006 | ...   let mut func_response = api::update_tags(rack_input.value(), change_input.value(), &global_token, config_data.clone()).await;
     |                                                                                                                             ^^^^^^

Line 1006 goes as follows:

let mut func_response = api::update_tags(rack_input.value(), change_input.value(), &global_token, config_data.clone()).await;

The update_tags function in the api module is defined as follows:

pub struct FunctionResponse {
    pub token: String,
    pub error: String,
}

pub async fn update_tags(rack: String, change: String, new_token: &String, config: ConfigData) -> FunctionResponse {

My main() function is defined as follows:

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

I cannot post the full code unfortunately, but I was hoping that someone could help give me an idea of what was going on because I am very confused.

[dogou77]

I tried to define the type of the Vector with the following code:

let mut tag_log_tasks: Vec<JoinHandle<_>> = Vec::new();

But I get the error:

error[E0698]: type inside `async` block must be known in this context
    --> src/main.rs:97:9
     |
97   |     let mut tag_log_tasks: Vec<JoinHandle<_>> = Vec::new();
     |         ^^^^^^^^^^^^^^^^^ cannot infer type
     |
note: the type is part of the `async` block because of this `await`
    --> src/main.rs:1004:139
     |
1004 | ...   let mut func_response = api::update_tags(rack_input.value(), change_input.value(), &global_token, config_data.clone()).await;
     |                                                                                                                             ^^^^^^

Now I understand that this is because the type inside JoinHandle isn't known (the <_> portion). Does anyone know if there is any type I can put inside there that would fix my issue? The code I am trying to store inside this vec goes as follows:

tokio::spawn(async move {
    tokio::time::sleep(Duration::from_secs(5)).await;
    log_buffer_clone.set_text("");
});

I appreciate the help.

[Darksonn]

It seems like you aren't returning anything from the task, in which case the return type is (). In that case, you would use JoinHandle<()> as the type.

I note that this error sometimes comes from another error inhibiting type inference. If there are also other errors, you may want to try and fix those first.

You may find this page on graceful shutdown useful.

[dogou77]

Thanks so much, the page you recommended is really useful.