refactor: prevent duplicate instances to be added to pool

packages/melonjs/src/system/pool.test.ts

@@ -31,6 +31,17 @@ test("can release objects from the pool", () => {
 	expect(pool.used()).toBe(1);
 });
 
+test("can not release instance that already exist in pool", () => {
+	const pool = createPool(() => {
+		return { instance: new GameObject() };
+	});
+	const object1 = pool.get();
+	pool.release(object1);
+	expect(() => {
+		pool.release(object1);
+	}).toThrow();
+});
+
 test("can manually purge", () => {
 	const pool = createPool(() => {
 		return { instance: new GameObject() };

packages/melonjs/src/system/pool.ts

@@ -1,3 +1,10 @@
+const takeFromSet = <T>(set: Set<T>) => {
+	for (const value of set) {
+		set.delete(value);
+		return value;
+	}
+};
+
 export interface Pool<T, A extends unknown[]> {
 	get(...args: A): T;
 	release(object: T): void;
@@ -16,7 +23,7 @@ export interface CreatePoolOptions<T, A extends unknown[]> {
 export const createPool = <T, A extends unknown[]>(
 	options: (...args: A) => CreatePoolOptions<T, A>,
 ): Pool<T, A> => {
-	const available: T[] = [];
+	const available = new Set<T>();
 	const instanceResetMethods = new Map<T, Reset<A>>();
 	let inUse: number = 0;
 
@@ -26,15 +33,18 @@ export const createPool = <T, A extends unknown[]>(
 		 * @param instance The object to release.
 		 */
 		release: (instance: T) => {
-			available.push(instance);
+			if (available.has(instance)) {
+				throw new Error("Instance is already in pool.");
+			}
+			available.add(instance);
 			inUse--;
 		},
 		/**
 		 * get an instance from the pool
 		 * @param args The arguments for creating the instance.
 		 */
 		get: (...args) => {
-			const object = available.pop();
+			const object = takeFromSet(available);
 			if (object) {
 				const reset = instanceResetMethods.get(object);
 				reset?.(...args);
@@ -51,14 +61,14 @@ export const createPool = <T, A extends unknown[]>(
 		 * purge the pool
 		 */
 		purge: () => {
-			available.length = 0;
+			available.clear();
 			inUse = 0;
 		},
 		/**
 		 * get the current size of the pool (how many objects are available)
 		 */
 		size: () => {
-			return available.length;
+			return available.size;
 		},
 		/**
 		 * get the number of objects currently in use