feat(util): managed scope and util for handling freeable objects

Author: rhyslbw

Diff for: packages/util/src/freeable.ts

@@ -0,0 +1,64 @@
+import { Freeable } from './types';
+
+/**
+ * A scope to ease the management of objects that require manual resource management.
+ *
+ */
+export class ManagedFreeableScope {
+  #scopeStack: Freeable[] = [];
+  #disposed = false;
+
+  /**
+   * Objects passed to this method will then be managed by the instance.
+   *
+   * @param freeable An object with a free function, or undefined. This makes it suitable for wrapping functions that
+   * may or may not return a value, to minimise the implementation logic.
+   * @returns The freeable object passed in, which can be undefined.
+   */
+  public manage<T extends Freeable | undefined>(freeable: T): T {
+    if (freeable === undefined) return freeable;
+    if (this.#disposed) throw new Error('This scope is already disposed.');
+    this.#scopeStack.push(freeable);
+    return freeable;
+  }
+
+  /**
+   * Once the freeable objects being managed are no longer being accessed, call this method.
+   */
+  public dispose(): void {
+    if (this.#disposed) return;
+    for (const resource of this.#scopeStack) {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      if ((resource as any)?.ptr === 0 || !resource?.free) {
+        continue;
+      }
+
+      resource?.free();
+    }
+    this.#disposed = true;
+  }
+}
+
+class AutoFree<TReturn> {
+  #scope: ManagedFreeableScope;
+  readonly #callback: (scope: ManagedFreeableScope) => TReturn;
+
+  constructor(cb: (scope: ManagedFreeableScope) => TReturn) {
+    this.#callback = cb;
+    this.#scope = new ManagedFreeableScope();
+  }
+
+  public execute() {
+    try {
+      return this.#callback(this.#scope);
+    } finally {
+      this.#scope.dispose();
+    }
+  }
+}
+
+/**
+ * A wrapper function to setup and dispose of a ManagedFreeableScope at the end of the callback execution.
+ */
+export const usingAutoFree = <TReturn>(cb: (scope: ManagedFreeableScope) => TReturn) =>
+  new AutoFree<TReturn>(cb).execute();

Diff for: packages/util/src/index.ts

@@ -1,4 +1,5 @@
 export * from './equals';
+export * from './freeable';
 export * from './types';
 export * from './BigIntMath';
 export * from './hexString';

Diff for: packages/util/src/types.ts

@@ -15,3 +15,7 @@ export type DeepPartial<T, O = never> = T extends O | Primitive
   : {
       [P in keyof T]?: DeepPartial<T[P], O>;
     };
+
+export interface Freeable {
+  free: () => void;
+}

Diff for: packages/util/test/freeable.test.ts

@@ -0,0 +1,59 @@
+import { Freeable, ManagedFreeableScope, usingAutoFree } from '../src';
+
+class FreeableEntity implements Freeable {
+  constructor(public id: number) {}
+  public getId(): number {
+    return this.id;
+  }
+  public free() {
+    void 0;
+  }
+}
+
+describe('freeable', () => {
+  describe('ManagedFreeableScope', () => {
+    it('manage returns undefined if argument passed is undefined', () => {
+      const scope = new ManagedFreeableScope();
+      const freeable = undefined;
+      const one = scope.manage(freeable);
+      expect(one).toBeUndefined();
+    });
+  });
+  describe('usingAutoFree', () => {
+    it('calls the object free method after executing callback', () => {
+      const entity = new FreeableEntity(1);
+      const spy = jest.spyOn(entity, 'free');
+      usingAutoFree((scope) => {
+        const one = scope.manage(entity);
+        expect(one.getId()).toBe(1);
+      });
+      expect(spy).toHaveBeenCalledTimes(1);
+    });
+
+    it('can return a value', () => {
+      const entity = new FreeableEntity(1);
+      const spy = jest.spyOn(entity, 'free');
+      const id = usingAutoFree((scope) => {
+        const one = scope.manage(entity);
+        return one.getId();
+      });
+      expect(id).toBe(1);
+      expect(spy).toHaveBeenCalledTimes(1);
+    });
+
+    it('can handle multiple objects', () => {
+      const firstEntity = new FreeableEntity(1);
+      const secondEntity = new FreeableEntity(2);
+      const firstSpy = jest.spyOn(firstEntity, 'free');
+      const secondSpy = jest.spyOn(secondEntity, 'free');
+      usingAutoFree((scope) => {
+        const one = scope.manage(firstEntity);
+        const two = scope.manage(secondEntity);
+        expect(one.getId()).toBe(1);
+        expect(two.getId()).toBe(2);
+      });
+      expect(firstSpy).toHaveBeenCalledTimes(1);
+      expect(secondSpy).toHaveBeenCalledTimes(1);
+    });
+  });
+});