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Is there a way to specify a single-threaded runtime using the attribute #[tokio::main] in tokio 0.2? The doc does not seem to have examples for that.

EDIT: I wanted to find a way to set up tokio runtime so that rustc is aware of tokio:spawn() will not be a new thread.

user1783732
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1 Answers1

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The documentation for tokio::main shows what options it has:

core_threads=n - Sets core threads to n (requires rt-threaded feature). max_threads=n - Sets max threads to n (requires rt-core or rt-threaded feature).

Thus:

#[tokio::main(core_threads = 1, max_threads = 1)]
async fn main() {
    println!("Hello world");
}

If this does not work for whatever your case is, you will have to directly create a runtime as shown in How do I synchronously return a value calculated in an asynchronous Future in stable Rust?.

Shepmaster
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  • Thanks for your answer. I should have clarified that I wanted to find a way to have tokio executor runs on the single (current) thread, instead of thread pool of size 1. The reason is that I wanted `rustc` is aware of all tasks are in a single thread, so no need to check for thread safety issues. Later I tried the approach of using `basic_scheduler`, but it seems that `rustc` still thinks it's a new thread when I call `tokio::spawn()`. – user1783732 May 14 '20 at 16:40
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    @user1783732 why wouldn’t you have asked the question you wanted to solve? You are demonstrating the [X-Y problem](https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem). Your problem [isn’t unique to Tokio or async](https://stackoverflow.com/q/32750829/155423) and shows a fundamental misunderstanding of what the Rust compiler is capable of. – Shepmaster May 14 '20 at 16:45
  • @user1783732 You can use [LocalSet](https://docs.rs/tokio/latest/tokio/task/struct.LocalSet.html) and `spawn_local` to limit execution to a single thread. It allows having `!Send` variable over `.await` boundary, which sounds like what you're looking for. – quartzsaber Jan 16 '22 at 15:03