Module task 

Task lifecycle types: TaskHeader, Task, JoinHandle.

Memory Model

Two separate heap allocations per spawned future:

1. Arc<TaskHeader> — shared between executor (Task), all Wakers, and JoinHandle. Contains the atomic state, vtable pointer, join-waker slot, and the output slot (written on completion, read by JoinHandle).

2. Box<TaskBody<F>> (stored as body_ptr: *mut () in TaskHeader) — owns the erased Pin<Box<F>> (the live future). Freed by the executor the moment the future resolves or the task is cancelled, independent of when the JoinHandle reads the output.

Separating the output from the body lets drop_body free the future immediately on completion while the output lives safely in the Arc until JoinHandle::poll retrieves it.

Thread Safety for Multi-Threaded Executor

join_waker is now protected by a Mutex to allow safe concurrent access between JoinHandle::poll (any worker thread) and poll_task / cancel (any background worker). The double-check pattern in JoinHandle::poll ensures the waker is never missed if a task completes concurrently.

Structs

JoinHandle

Future returned from spawn(). Resolves when the spawned task completes.

Enums

JoinError

Error returned by a JoinHandle when the task does not complete normally.