Cannot start a runtime from within a runtime

[Virgil-N]

Version
1.22.0

Platform
Mac M1

Description
Enter your issue details here.
One way to structure the description:

I tried this code:

let rt1 = tokio::runtime::Runtime::new().unwrap();
rt1.block_on(async {
    self.render_news_cards(ui).await;
});

start with cargo run, error occurs:
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 while the thread is being used to drive asynchronous tasks.'

How to fix it?

[Darksonn]

Your code example is too small to show what the issue is. Did you write that code inside a #[tokio::main] function? If you're using block_on, then you shouldn't use #[tokio::main].

[Darksonn]

The #[tokio::main] attr creates a runtime, which you should only do once.

[Virgil-N]

Can't nest?

[Darksonn]

No, runtimes cannot nest.

[Virgil-N]

Got it.

[ShyunnY]

@Darksonn

I have a problem: the third-party crate I introduced manually builds the async Runtime through tokio::runtime::Builder. At this time, I need to reference this crate in my project.

Based on your discussion, can I understand that when I introduce this crate, I cannot add [tokio::main] to fn main(), otherwise it will not work properly.

Is my understanding correct?