Rust Async With Tokio: Tasks, Await, And Executor Basics

Rust **`async fn`** syntax desugars to state machines implementing the **`Future`** trait. **Tokio** is the dominant async runtime for networking: TCP, timers, and task scheduling on thread pools documented at `tokio.rs`.

`tokio::spawn` runs concurrent tasks on the runtime. `.await` yields at I/O boundaries without blocking OS threads. CPU-bound work belongs on `spawn_blocking` or dedicated worker pools to avoid starving the reactor.

Ecosystem crates (`hyper`, `axum`, `tonic`, `sqlx`) build on Tokio. Choose **`current_thread`** for embedded CLIs and **multi-thread** runtimes for servers.

Rust async error handling uses `Result` and libraries like `anyhow` or `thiserror`. Read the Tokio tuning guide before production: set worker thread counts from CPU cores and measure latency under load.