Scheduler

The async scheduler is the only supported execution backend. User code runs inside it automatically — no setup required.

Architecture

On Linux, the scheduler is a single-threaded event loop backed by io_uring. On other platforms (macOS, CI), a threadpool-based backend provides the same interface using blocking I/O on background threads.

All I/O operations (port reads/writes, TCP, subprocess) yield to the scheduler, which submits them to the backend and resumes the fiber when the operation completes.

┌─────────────┐
│  User fiber  │ ← ev/spawn creates these
│  (yield :io) │
└──────┬───────┘
       │ submit to io_uring
       ▼
┌─────────────┐
│  Event loop  │ ← io/wait polls completions
│  (io_uring)  │
└──────┬───────┘
       │ completion → resume fiber
       ▼
┌─────────────┐
│  User fiber  │ ← continues after yield
│  (result)    │
└─────────────┘

ev/run

ev/run is the scheduler's entry point. The runtime calls it automatically for user code. You rarely need to call it directly.

io/wait

The scheduler's poll loop. Waits for io_uring completions and resumes waiting fibers. Called internally by the event loop.

Signal integration

I/O operations signal :io when they yield. The fiber's signal mask must include :io (the async scheduler sets this up automatically for spawned fibers).

Timer support