Struct BatchGuard 

pub struct BatchGuard { /* private fields */ }

RAII guard returned by Core::begin_batch.

While alive, suppresses per-emit wave drains — multiple emit / complete / error / teardown / invalidate calls coalesce into one wave. On drop:

• Outermost guard: drains the wave (fires sinks, runs cleanup, clears in-tick).
• Nested guard (an outer BatchGuard or an in-progress wave already owns the in-tick flag): silently no-ops.

On thread panic during the closure body, the drop path discards pending tier-3+ delivery rather than firing sinks (avoids cascading panics). Subscribers observe no tier-3+ delivery for the panicked wave. State-node cache writes that already executed inside the closure are rolled back via wave-cache snapshots — cache_of(s) returns the pre- panic value. The atomicity guarantee covers both sink-observability and cache state.

Thread safety

BatchGuard is !Send by design. begin_batch claims the per-Core in_tick flag AND the per-partition wave_owner re-entrant mutex(es) on the calling thread; sending the guard to another thread and dropping it there would clear in_tick and release the wave-owner guards from a different thread than the one that acquired them, breaking both the thread-local “I own the wave scope” semantic and parking_lot::ReentrantMutex’s ownership invariant. The _wave_guards field is a SmallVec of !Send ArcReentrantMutexGuard<()>; the PhantomData<*const ()> marker is belt-and-suspenders.

Slice Y1 / Phase E (2026-05-08): the field migrated from a single ArcReentrantMutexGuard (legacy Core-global wave_owner) to a SmallVec of partition wave-owner guards. Closure-form begin_batch acquires every current partition (serialization point); begin_batch_for(seed) acquires only the transitively- touched partitions (parallel for disjoint sets).

use graphrefly_core::{BatchGuard, BindingBoundary, Core, DepBatch, FnId, FnResult, HandleId, NodeId};
use std::sync::Arc;

struct Stub;
impl BindingBoundary for Stub {
    fn invoke_fn(&self, _: NodeId, _: FnId, _: &[DepBatch]) -> FnResult {
        FnResult::Noop { tracked: None }
    }
    fn custom_equals(&self, _: FnId, _: HandleId, _: HandleId) -> bool { false }
    fn release_handle(&self, _: HandleId) {}
}
fn requires_send<T: Send>(_: T) {}
let core = Core::new(Arc::new(Stub) as Arc<dyn BindingBoundary>);
let guard = core.begin_batch();
requires_send(guard); // <- compile_fail: BatchGuard is !Send.

Trait Implementations

impl Drop for BatchGuard

fn drop(&mut self)

Executes the destructor for this type.