From b461e2ee92ca203061d85ea0a862a06bd132fb69 Mon Sep 17 00:00:00 2001
From: Erik Onarheim <erik.onarheim@gmail.com>
Date: Mon, 1 Jun 2026 21:09:56 -0500
Subject: [PATCH] fix: possible mem leak on query entity removal (#3768)

---
 .../entity-component-system/query-manager.ts  | 13 ++++---
 src/spec/vitest/query-manager-spec.ts         | 37 +++++++++++++++++++
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/src/engine/entity-component-system/query-manager.ts b/src/engine/entity-component-system/query-manager.ts
index 53bd4b8c..51e049df 100644
--- a/src/engine/entity-component-system/query-manager.ts
+++ b/src/engine/entity-component-system/query-manager.ts
@@ -58,7 +58,7 @@ export class QueryManager {
     }
 
     for (const entity of this._world.entities) {
-      this.addEntity(entity);
+      query.checkAndModify(entity);
     }
 
     return query;
@@ -85,6 +85,7 @@ export class QueryManager {
    * @param entity
    */
   addEntity(entity: Entity) {
+    const alreadyTracked = this._addComponentHandlers.has(entity);
     const maybeAddComponent = this._addComponentHandlers.get(entity);
     const maybeRemoveComponent = this._removeComponentHandlers.get(entity);
     const addComponent = maybeAddComponent ?? this._createAddComponentHandler(entity);
@@ -103,10 +104,12 @@ export class QueryManager {
       query.checkAndModify(entity);
     }
 
-    entity.componentAdded$.subscribe(addComponent);
-    entity.componentRemoved$.subscribe(removeComponent);
-    entity.tagAdded$.subscribe(addTag);
-    entity.tagRemoved$.subscribe(removeTag);
+    if (!alreadyTracked) {
+      entity.componentAdded$.subscribe(addComponent);
+      entity.componentRemoved$.subscribe(removeComponent);
+      entity.tagAdded$.subscribe(addTag);
+      entity.tagRemoved$.subscribe(removeTag);
+    }
   }
 
   /**
diff --git a/src/spec/vitest/query-manager-spec.ts b/src/spec/vitest/query-manager-spec.ts
index 80f272cd..4dd4eb8b 100644
--- a/src/spec/vitest/query-manager-spec.ts
+++ b/src/spec/vitest/query-manager-spec.ts
@@ -257,6 +257,43 @@ describe('A QueryManager', () => {
     expect(queryAB.getEntities()).toEqual([]);
   });
 
+  it('does not duplicate entity subscriptions when creating queries after entities exist', () => {
+    const world = new ex.World(null);
+    const entity = new ex.Entity();
+    entity.addComponent(new FakeComponentA());
+    entity.addTag('A');
+
+    world.add(entity);
+
+    expect(entity.componentAdded$.subscriptions.length).toBe(1);
+    expect(entity.componentRemoved$.subscriptions.length).toBe(1);
+    expect(entity.tagAdded$.subscriptions.length).toBe(1);
+    expect(entity.tagRemoved$.subscriptions.length).toBe(1);
+
+    world.query([FakeComponentA]);
+    world.query([FakeComponentB]);
+    world.queryTags(['A']);
+    world.queryTags(['B']);
+
+    expect(entity.componentAdded$.subscriptions.length).toBe(1);
+    expect(entity.componentRemoved$.subscriptions.length).toBe(1);
+    expect(entity.tagAdded$.subscriptions.length).toBe(1);
+    expect(entity.tagRemoved$.subscriptions.length).toBe(1);
+  });
+
+  it('does not duplicate entity subscriptions when addEntity is called more than once', () => {
+    const world = new ex.World(null);
+    const entity = new ex.Entity();
+
+    world.queryManager.addEntity(entity);
+    world.queryManager.addEntity(entity);
+
+    expect(entity.componentAdded$.subscriptions.length).toBe(1);
+    expect(entity.componentRemoved$.subscriptions.length).toBe(1);
+    expect(entity.tagAdded$.subscriptions.length).toBe(1);
+    expect(entity.tagRemoved$.subscriptions.length).toBe(1);
+  });
+
   it('can update queries when a component is removed', () => {
     const world = new ex.World(null);
     const entity1 = new ex.Entity();
-- 
2.51.2