You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sched.rs
    path of file: ./repos/wasmtime/crates/wasi-common/src/tokio
    
    the code of the file until where you have to start completion: #[cfg(unix)]
mod unix;
#[cfg(unix)]
pub use unix::poll_oneoff;

#[cfg(windows)]
mod windows;
#[cfg(windows)]
pub use windows::poll_oneoff
    
pub fn sched_ctx() -> Box<dyn crate::WasiSched> {
    struct AsyncSched;

    #[wiggle::async_trait]
    impl WasiSched for AsyncSched {
        async fn poll_oneoff<'a>(&self, poll: &mut Poll<'a>) -> Result<(), Error> {
            poll_oneoff(poll).await
        }
        async fn sched_yield(&self) -> Result<(), Error> {
            tokio::task::yield_now().await;
            Ok(())
        }
        async fn sleep(&self, duration: Duration) -> Result<(), Error> {
            tokio::time::sleep(duration).await;
            Ok(())
        }
    }

    Box::new(AsyncSched)
}