resource-pool.ts

interface ResourcePoolOptions<T> {
  defaultSize: number;
  maxSize: number;
  create: () => T;
}

interface Resource<T> extends Disposable {
  value: T;
}

class ResourcePool<T> {
  #free: Set<T>;
  #claimed: Set<T>;
  #defaultSize: number;
  #maxSize: number;
  #create: () => T;

  constructor({defaultSize, maxSize, create}: ResourcePoolOptions<T>) {
    this.#free = new Set(Array.from({length: defaultSize}, () => create()));
    this.#claimed = new Set();
    this.#defaultSize = defaultSize;
    this.#maxSize = maxSize;
    this.#create = create;
  }

  get size(): number {
    return this.#free.size + this.#claimed.size;
  }

  get(): Resource<T> {
    if (this.#free.size > 0) {
      const [value] = this.#free.values();
      this.#free.delete(value);
      this.#claimed.add(value);

      return {
        value,
        [Symbol.dispose]: () => {
          this.#claimed.delete(value);
          this.#free.add(value);
        }
      }
    } else if (this.size < this.#maxSize) {
      this.#free.add(this.#create());
      return this.get();
    } else {
      throw new Error('max size exceeded');
    }
  }
}

const pool = new ResourcePool<ArrayBuffer>({
  defaultSize: 20,
  maxSize: 50,
  create: () => new ArrayBuffer(100),
});

using resource = pool.get();
const buffer = resource.value;