Rust Async Patterns Skill

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

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