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: limits.rs
    path of file: ./repos/cube/rust/cubestore/cubestore/src/import
    
    the code of the file until where you have to start completion: use crate::CubeError;
use std::sync::Arc;
use tokio
    
/// async fn do_work(limits: &ConcurrencyLimits) {
///     loop // run processing in parallel, but limit the number of active data frames.
///     {
///         let permit = limits.acquire_data_frame().await?;
///         // ... read data frame
///         tokio::spawn(async move || {
///             // ... process data frame
///             std::mem::drop(permit)
///         })
///     }
/// }