Struct PendingErrorCell 

pub struct PendingErrorCell(/* private fields */);

Interior-mutable slot for the renderer’s pending error-scope value.

This is the euv-engine analog of euv-core’s HandlerRegistryCell (core/src/renderer/registry/struct.rs:62): a single-element Sync wrapper that holds an Option<JsValue> behind an UnsafeCell.

Why this type exists

WebGpuRenderer::pending_error needs interior mutability because:

1. pop_error_sync takes &self (the WebGPU hot path cannot be async), but the spawned wasm_bindgen_futures::spawn_local future must mutate the slot to store the resolved Promise<GPUError?> value.
2. take_last_error also takes &self and drains the slot on the next render tick.

The first implementation used Rc<RefCell<Option<JsValue>>>, which works but pays for:

• a RefCell::borrow_mut runtime borrow check on every write (the panic path is unreachable in practice — only the spawn_local future and take_last_error ever touch the slot, and they never overlap because the future is a microtask drained before the next render tick).
• a heap allocation for the RefCell’s borrow state.

The newtype keeps the interior-mutability primitive (Rc), because the spawn_local future needs its own owning handle, but swaps the inner cell from RefCell to UnsafeCell:

• zero runtime borrow check (the WASM single-threaded scheduler makes the borrow impossible to violate).
• zero allocation (the cell is just a *mut Option<JsValue> sitting inside the Rc-managed box).

Sync safety

PendingErrorCell is not Sync by default (UnsafeCell explicitly opts out). We hand-implement Sync for it because the renderer is only ever used in the WASM single-threaded runtime; the Rc ensures the same instance is never shared across threads (it is not Send/Sync either), and the WASM main thread is the only place that ever touches the slot. This matches euv-core’s pattern (unsafe impl Sync for HandlerRegistryCell {}).

If the engine is ever compiled for a multi-threaded target (native, wasm-bindgen-rayon), this unsafe impl Sync is unsound and must be removed.

Implementations

impl PendingErrorCell

pub fn new() -> Self

Construct a new, empty pending-error slot.

The inner UnsafeCell<Option<JsValue>> starts as None; the WebGPU pop_error_sync microtask is the only thing that ever writes to it, and take_last_error is the only reader.

pub fn as_ptr(&self) -> *mut Option<JsValue>

Hand out a raw pointer to the inner cell for the wasm_bindgen_futures::spawn_local closure to write through.

Safety

The returned pointer is only valid for the lifetime of &self, and only safe to write to on the WASM main thread. The caller must guarantee that no other code is reading the same PendingErrorCell concurrently — this is enforced by the single-threaded scheduler: the spawned future is drained before the next render tick’s take_last_error runs.

Trait Implementations

impl Default for PendingErrorCell

fn default() -> Self

Returns the “default value” for a type.

impl Sync for PendingErrorCell