Simple Async Runtime

Futures Are State Machines You Poll

async fn in Rust desugars to a type implementing Future. tokio, hyper, and axum all boil down to executors calling poll until Poll::Ready. No magic threads: cooperative tasks yield at .await.

rustCopy
Loading…

• Poll::Pending: not done; store the Waker from cx and call it when I/O completes
• Poll::Ready(v): finish the task with value v
• Pin: many futures are self-referential; moving them after poll is UB

A Minimal Executor Loop

rustCopy
Loading…

Real runtimes integrate epoll/kqueue and timer wheels; yours can spin for teaching.

For this exercise, you will implement a tiny executor that polls spawned futures until idle. This task asks you to wire a Waker that requeues tasks, because debugging tokio hangs without understanding poll/wake is guesswork.

Keep the relevant man page, ABI doc, or Rust reference chapter open while you work. When your output disagrees with the reference implementation on the same machine, the mismatch is usually an alignment rule, an off-by-one terminator, or a register slot you misread in GDB. Skim the official documentation for the tool or ABI named in the exercise; the prose changes, but register roles, syscall numbers, and ownership rules stay stable across releases.