Rust: What is the difference between sync::Semaphore and tokio::sync::Semaphore?

1// Blocking
2use std::sync::Semaphore;
3let sem = Semaphore::new(5);
4let _permit = sem.acquire().unwrap();
5
6// Async
7use tokio::sync::Semaphore;
8let sem = Semaphore::new(5);
9let _permit = sem.acquire().await.unwrap();