Implement Async Rust Patterns with Tokio

Rust Async Patterns provides implementation patterns for asynchronous Rust applications using Tokio. It explains futures as lazy computations polled by a runtime, with await suspending execution until a future completes and tasks allowing work to proceed concurrently. The examples span task execution, communication, errors, shutdown, traits, streams, shared resources, and diagnostics.

Concurrent execution uses JoinSet to manage spawned tasks and distinguish task failures from join failures. A stream-based alternative applies buffer_unordered to constrain concurrent work. The select macro races futures when the workflow should proceed with the first completed result. These approaches let a developer choose between collecting multiple results, limiting parallel activity, and selecting one outcome.

Use it for async Rust applications, concurrent network services, Tokio-based I/O, error handling, performance work, or diagnosing asynchronous behavior. Clarify the goals, constraints, and required inputs before choosing patterns, then validate the resulting behavior in the target application.

Avoid blocking an async task with a thread sleep, holding locks across awaits, spawning work without bounds, or ignoring errors. Spawned futures also need the appropriate Send bounds. Prefer channels over shared mutable state when the workflow allows it. The examples are patterns to adapt rather than a substitute for environment-specific testing.

Inputs include asynchronous operations, concurrency limits, message types, application errors, and shutdown requirements. Outputs include collected task results, bounded streams, typed errors, and coordinated cancellation behavior. Channel options cover multi-producer single-consumer messages, broadcast delivery, a single-use result through oneshot, and the latest value through watch.

Error handling combines anyhow context for application failures with thiserror-based service errors and timeout wrappers. Shutdown examples use CancellationToken or a broadcast signal to notify workers after a control-C event. Async traits describe repository operations, with an implementation backed by a PostgreSQL pool.

Stream examples create delayed values, filter and map them, process chunks, and merge multiple streams. Resource patterns use RwLock for read-heavy shared data, Mutex for exclusive access, and Semaphore to constrain resource acquisition. These patterns make limits and synchronization explicit instead of allowing unbounded work.

A dependency excerpt is:

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

The examples also use SQLx for database access and tokio-util for cancellation. Tracing instrumentation attaches context to async functions and spawned tasks. The tokio-console tool is presented as a runtime diagnostic tool, with the corresponding tracing configuration needed for its use.