Struct Executor 

pub struct Executor { /* private fields */ }

Single-threaded async executor.

Manages task lifecycle: spawn, poll, complete, free. Tasks are allocated via Box (default) or slab (via spawn_slab). Each task’s header contains a free_fn that knows how to deallocate its own storage — the executor doesn’t know or care which allocator was used.

UnsafeCell on incoming and deferred_free

These fields are wrapped in UnsafeCell to prevent a provenance aliasing violation. During poll(), raw pointers to these Vecs are stored in TLS for wakers to push into. Later in the same poll(), complete_task(&mut self) takes &mut self — which under Rust’s aliasing rules asserts exclusive access to ALL fields. Without UnsafeCell, this invalidates the TLS pointers because two &mut paths to the same memory exist. UnsafeCell opts these fields out of &mut’s exclusivity guarantee, telling the compiler they may be accessed through other paths (the TLS raw pointers).

This is NOT a performance concern — UnsafeCell is zero-sized and get() compiles to a no-op pointer cast. The only effect is that the compiler won’t optimize based on exclusive access to these fields.

Implementations

impl Executor

pub fn new(initial_capacity: usize) -> Self

Create an executor.

pub fn spawn_boxed<F>(&mut self, future: F) -> JoinHandle<F::Output>

where F: Future + 'static, F::Output: 'static,

Spawn an async task via Box allocation. Returns a JoinHandle that can be awaited for the task’s output.

pub fn poll(&mut self) -> usize

Poll all ready tasks once.

pub fn task_count(&self) -> usize

Number of live tasks.

pub fn has_ready(&self) -> bool

Returns true if any tasks are queued for polling.

pub fn set_tasks_per_cycle(&mut self, limit: usize)

Set the maximum tasks to poll per cycle.

Trait Implementations

impl Drop for Executor

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.