change ticks

crates/bevy_ecs/src/world/mod.rs

@@ -2,7 +2,7 @@ mod entity_ref;
 mod spawn_batch;
 mod world_cell;
 
-pub use crate::change_detection::Mut;
+pub use crate::change_detection::{Mut, CHECK_TICK_THRESHOLD};
 pub use entity_ref::*;
 pub use spawn_batch::*;
 pub use world_cell::*;
@@ -91,6 +91,7 @@ pub struct World {
     main_thread_validator: MainThreadValidator,
     pub(crate) change_tick: AtomicU32,
     pub(crate) last_change_tick: u32,
+    pub(crate) last_check_tick: u32,
 }
 
 impl Default for World {
@@ -109,6 +110,7 @@ impl Default for World {
             // are detected on first system runs and for direct world queries.
             change_tick: AtomicU32::new(1),
             last_change_tick: 0,
+            last_check_tick: 0,
         }
     }
 }
@@ -1399,15 +1401,31 @@ impl World {
         self.last_change_tick
     }
 
+    /// All component change ticks are scanned for risk of age overflow once the world counter
+    /// has incremented at least [`CHECK_TICK_THRESHOLD`](crate::change_detection::CHECK_TICK_THRESHOLD)
+    /// times since the previous `check_change_ticks` scan.
+    ///
+    /// During each scan, any change ticks older than [`MAX_CHANGE_AGE`](crate::change_detection::MAX_CHANGE_AGE)
+    /// are clamped to that age. This prevents false positives that would appear because of overflow.
+    // TODO: parallelize
     pub fn check_change_ticks(&mut self) {
-        // Iterate over all component change ticks, clamping their age to max age
-        // PERF: parallelize
+        let last_check_tick = self.last_check_tick;
         let change_tick = self.change_tick();
-        self.storages.tables.check_change_ticks(change_tick);
-        self.storages.sparse_sets.check_change_ticks(change_tick);
-        let resource_archetype = self.archetypes.resource_mut();
-        for column in resource_archetype.unique_components.values_mut() {
-            column.check_change_ticks(change_tick);
+        if change_tick.wrapping_sub(last_check_tick) >= CHECK_TICK_THRESHOLD {
+            #[cfg(feature = "trace")]
+            let _span = bevy_utils::tracing::info_span!("check component ticks").entered();
+            self.storages.tables.check_change_ticks(change_tick);
+            self.storages.sparse_sets.check_change_ticks(change_tick);
+            let resource_archetype = self.archetypes.resource_mut();
+            for column in resource_archetype.unique_components.values_mut() {
+                column.check_change_ticks(change_tick);
+            }
+
+            if let Some(mut systems) = self.get_resource_mut::<crate::schedule_v3::Systems>() {
+                systems.check_change_ticks(change_tick, last_check_tick);
+            }
+
+            self.last_check_tick = change_tick;
         }
     }