Why Async?
When your server handles thousands of concurrent connections, you need async. Thread-per-connection does not scale. Async lets a single thread multiplex thousands of I/O operations without blocking.
Tokio Fundamentals
Tokio provides the runtime, the I/O primitives, and the synchronization tools you need. The key types are tokio::spawn for tasks, mpsc channels for communication, and select! for waiting on multiple futures.
Pattern: Fan-Out, Fan-In
Spawn multiple tasks to handle work in parallel, collect results through a channel. This pattern powers everything from web scrapers to API aggregators.
Common Mistakes
- Holding a mutex across an await point (deadlock potential)
- Spawning too many tasks without backpressure
- Blocking the async runtime with synchronous code
The Takeaway
Async Rust has a learning curve, but the performance payoff is enormous. A well-written async Rust server can handle 100K+ concurrent connections on modest hardware.