Tokio Runtime Setup

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Tokio Tutorial(DOCUMENTATION)

Introduction

Tokio is the most widely used async runtime for Rust. It provides a multi-threaded work-stealing executor, async I/O, timers, and synchronization primitives. Setup starts with the #[tokio::main] macro.

Key Concepts

Quick start:

toml
[dependencies]
tokio = { version = "1", features = ["full"] }
rust
#[tokio::main]
async fn main() {
    println!("Hello from Tokio!");
}

This expands to:

rust
fn main() {
    tokio::runtime::Runtime::new()
        .unwrap()
        .block_on(async { println!("Hello from Tokio!"); });
}

Real World Context

Most production Rust services use #[tokio::main] at the entry point. Feature gates let you pull in only what you need for smaller binaries.

Deep Dive

Runtime flavors:

rust
// Multi-threaded (default) — work-stealing scheduler
#[tokio::main]
async fn main() { }

// Single-threaded — no Send requirement, simpler
#[tokio::main(flavor = "current_thread")]
async fn main() { }

// Custom worker count
#[tokio::main(worker_threads = 4)]
async fn main() { }

Manual Runtime::Builder for full control:

rust
let rt = tokio::runtime::Builder::new_multi_thread()
    .worker_threads(4)
    .thread_name("my-worker")
    .enable_all()
    .build()?;

rt.block_on(async {
    // Your async code here
});

Feature gates — don't use "full" in production if you want minimal binaries:

toml
tokio = { version = "1", features = ["rt", "macros", "net", "time"] }

Common Pitfalls

  • Using "full" features in a library crate — let consumers choose
  • Forgetting enable_all() on manual builders — I/O and timers won't work
  • Using current_thread when spawned tasks need Send across threads

Best Practices

  • Use #[tokio::main] for applications, manual builder for libraries
  • Select only the features you need
  • Use current_thread for simple tools and tests

Summary

#[tokio::main] is the standard entry point. Choose multi_thread (default) or current_thread. Use Runtime::Builder for advanced configuration. Select minimal feature gates for production.

Code Examples

rust
// Feature-gated setup for smaller binaries
// Cargo.toml: tokio = { version = "1", features = ["rt", "macros"] }

#[tokio::main(flavor = "current_thread")]
async fn main() {
    println!("Lightweight single-threaded runtime!");
}

// For tests: #[tokio::test] works the same way
#[tokio::test]
async fn my_test() {
    assert_eq!(2 + 2, 4);
}
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