Module task 

Task types, generic future storage, and the task registry.

Tasks are placed in the .rivet_tasks linker section for discovery by the executor at startup. Each entry is a TaskReg — just the metadata the executor needs to poll a task. The task’s actual Future state machine lives in a TaskCell, sized generically and monomorphized per concrete future type.

Why not static TASK: TaskCell<F> = ...?

F is the compiler-generated, unnameable type of an async fn’s Future. Stable Rust cannot name that type in a static declaration (that requires type_alias_impl_trait, nightly-only). Instead, TaskCell is generic over a usize byte size, which is nameable (TaskCell<512>), and the actual read/write of the future happens inside a generic method (TaskCell::poll::<F>) that the compiler monomorphizes separately for each task’s concrete F. This gets real async fn tasks with static, zero-allocation storage on 100% stable Rust.

Structs

TaskCell

Generic, zero-allocation storage for one task’s Future state machine.

TaskId

The unified identity of a cooperative-tier task: (priority, index) packed into one u16, used by the waker, executor, timer queue, semaphore, and channel (plan.md [B12] — replaces two ad-hoc encodings (prio << 24) | index and (prio << 8) | index).

TaskReg

Registration entry placed in the .rivet_tasks linker section. The executor walks these to discover all statically-declared tasks.

Constants

DEFAULT_TASK_SIZE

Default byte size reserved for a task’s future state machine when the user doesn’t override it with #[rivet::task(stack = N)].

MAX_PRIORITY

Maximum priority level (0 = lowest, 31 = highest).

MAX_TASKS

Maximum number of tasks per priority level (RIVET_MAX_COOP_TASKS).

TASK_CELL_ALIGN

Alignment guaranteed for future storage inside a TaskCell. Covers all primitive/usize/u64-aligned types used in typical embedded futures. TaskCell::poll asserts this at runtime on first use.