Rust Async Patterns

Production patterns for async Rust programming with Tokio runtime, including tasks, channels, streams, and error handling.

When to Use This Skill

• Building async Rust applications
• Implementing concurrent network services
• Using Tokio for async I/O
• Handling async errors properly
• Debugging async code issues
• Optimizing async performance

Core Concepts

1. Async Execution Model

Future (lazy) → poll() → Ready(value) | Pending
                ↑           ↓
              Waker ← Runtime schedules

2. Key Abstractions

Concept	Purpose
Future	Lazy computation that may complete later
async fn	Function returning impl Future
await	Suspend until future completes
Task	Spawned future running concurrently
Runtime	Executor that polls futures

Quick Start

# Cargo.toml
[dependencies]
tokio = { version = "1", features = ["full"] }
futures = "0.3"
async-trait = "0.1"
anyhow = "1.0"
tracing = "0.1"
tracing-subscriber = "0.3"

use tokio::time::{sleep, Duration};
use anyhow::Result;

#[tokio::main]
async fn main() -> Result<()> {
    // Initialize tracing
    tracing_subscriber::fmt::init();

    // Async operations
    let result = fetch_data("https://api.example.com").await?;
    println!("Got: {}", result);

    Ok(())
}

async fn fetch_data(url: &str) -> Result<String> {
    // Simulated async operation
    sleep(Duration::from_millis(100)).await;
    Ok(format!("Data from {}", url))
}

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Best Practices

Do's

• Use tokio::select! - For racing futures
• Prefer channels - Over shared state when possible
• Use JoinSet - For managing multiple tasks
• Instrument with tracing - For debugging async code
• Handle cancellation - Check CancellationToken

Don'ts

• Don't block - Never use std::thread::sleep in async
• Don't hold locks across awaits - Causes deadlocks
• Don't spawn unboundedly - Use semaphores for limits
• Don't ignore errors - Propagate with ? or log
• Don't forget Send bounds - For spawned futures