Struct MicrotaskQueue 

pub struct MicrotaskQueue { /* private fields */ }

The microtask queue — drained completely after each macrotask.

Like Chrome’s microtask queue in V8::MicrotaskQueue / Blink’s EventLoop::PerformMicrotaskCheckpoint().

Spec behavior

“If the microtask queue is not empty:

1. Let oldestMicrotask be the result of dequeuing from microtask queue.
2. Set event loop’s currently running task to oldestMicrotask.
3. Run oldestMicrotask.
4. Set event loop’s currently running task back to null.
5. Go to step 1.“

Key: microtasks enqueued DURING drain are also drained in the same cycle.

Implementations

impl MicrotaskQueue

pub fn new() -> Self

Create an empty microtask queue.

pub fn enqueue(&mut self, microtask: Microtask)

Enqueue a microtask.

If called during drain(), the new microtask will be processed in the same drain cycle.

pub fn queue_microtask(&mut self, callback: impl FnOnce() + 'static)

Convenience: enqueue a closure as a microtask.

pub fn drain(&mut self) -> usize

Drain the microtask queue completely (microtask checkpoint).

Runs all microtasks, including any new ones enqueued during drain. Returns the number of microtasks executed.

Re-entrancy

This takes microtasks one at a time via pop_front(). If a microtask enqueues more, they appear at the back and will be processed before drain() returns. To prevent infinite loops from buggy user code, a safety limit is enforced.

pub fn len(&self) -> usize

Number of pending microtasks.

pub fn is_empty(&self) -> bool

Whether the microtask queue is empty.

Trait Implementations

impl Default for MicrotaskQueue

fn default() -> Self

Returns the “default value” for a type.