How to Limit Concurrency in Async Rust (Semaphore)

Use tokio::sync::Semaphore to limit concurrent async tasks by acquiring a permit before execution. Add tokio to your Cargo.toml and wrap your async logic in a permit block to enforce the limit.

use tokio::sync::Semaphore;

#[tokio::main]
async fn main() {
    let semaphore = Semaphore::new(5);
    let mut handles = vec![];

    for _ in 0..100 {
        let sem = semaphore.clone();
        let handle = tokio::spawn(async move {
            let _permit = sem.acquire().await.unwrap();
            // Your async work here
        });
        handles.push(handle);
    }

    for handle in handles {
        handle.await.unwrap();
    }
}

A semaphore acts like a ticket booth that only lets a specific number of people enter a room at once. You use it in async Rust to prevent too many tasks from running simultaneously, which protects your system from crashing due to overload. It ensures that only the allowed number of operations happen at any given moment.