Rust async and Tokio

Lesson 1.3 previewed this — now we go deep.

One thread, many tasks

Tokio multiplexes thousands of async tasks on a small thread pool. When code hits .await, the task yields so other webhooks can run.

TokioFutureMachine walks: idle → poll → await Kafka → resume → HTTP response.

Not the browser event loop

	Browser JS	Rust Tokio
Scheduler	Single thread + microtasks	Thread pool + cooperative tasks
Blocking	Blocks the tab	spawn_blocking for CPU/sync I/O
Example	TanStack refetch	ingestion Kafka publish

Read the real handler

Open services/ingestion/src/main.rs — find github_webhook and mark every .await.

Teach-back prompt

What happens to other requests while one handler awaits Kafka?