fix: run GC before collecting open handles

CHANGELOG.md

@@ -50,6 +50,7 @@
 - `[jest-console]` `console.dir` now respects the second argument correctly ([#10638](https://github.com/facebook/jest/pull/10638))
 - `[jest-core]` Don't report PerformanceObserver as open handle ([#11123](https://github.com/facebook/jest/pull/11123))
 - `[jest-core]` Use `WeakRef` to hold timers when detecting open handles ([#11277](https://github.com/facebook/jest/pull/11277))
+- `[jest-core]` Run GC detecting open handles ([#11278](https://github.com/facebook/jest/pull/11278))
 - `[jest-each]` [**BREAKING**] Ignore excess words in headings ([#8766](https://github.com/facebook/jest/pull/8766))
 - `[jest-environment]` [**BREAKING**] Drop support for `runScript` for test environments ([#11155](https://github.com/facebook/jest/pull/11155))
 - `[jest-environment-jsdom]` Use inner realm’s `ArrayBuffer` constructor ([#10885](https://github.com/facebook/jest/pull/10885))

e2e/__tests__/detectOpenHandles.ts

@@ -71,6 +71,17 @@ it('does not report promises', () => {
   expect(textAfterTest).toBe('');
 });
 
+it('does not report crypto random data', () => {
+  // The test here is basically that it exits cleanly without reporting anything (does not need `until`)
+  const {stderr} = runJest('detect-open-handles', [
+    'crypto',
+    '--detectOpenHandles',
+  ]);
+  const textAfterTest = getTextAfterTest(stderr);
+
+  expect(textAfterTest).toBe('');
+});
+
 onNodeVersions('>=11.10.0', () => {
   it('does not report ELD histograms', () => {
     const {stderr} = runJest('detect-open-handles', [

e2e/detect-open-handles/__tests__/crypto.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const {randomFillSync} = require('crypto');
+
+test('randomFillSync()', () => {
+  const buf = Buffer.alloc(10);
+  randomFillSync(buf);
+});

packages/jest-core/src/collectHandles.ts

@@ -8,12 +8,15 @@
 /* eslint-disable local/ban-types-eventually */
 
 import * as asyncHooks from 'async_hooks';
+import {promisify} from 'util';
+import {setFlagsFromString} from 'v8';
+import {runInNewContext} from 'vm';
 import stripAnsi = require('strip-ansi');
 import type {Config} from '@jest/types';
 import {formatExecError} from 'jest-message-util';
 import {ErrorWithStack} from 'jest-util';
 
-export type HandleCollectionResult = () => Array<Error>;
+export type HandleCollectionResult = () => Promise<Array<Error>>;
 
 function stackIsFromUser(stack: string) {
   // Either the test file, or something required by it
@@ -41,6 +44,21 @@ const alwaysActive = () => true;
 
 const hasWeakRef = typeof WeakRef === 'function';
 
+const tick = promisify(setImmediate);
+
+function runGarbageCollector() {
+  const isGarbageCollectorHidden = !global.gc;
+
+  // GC is usually hidden, so we have to expose it before running.
+  setFlagsFromString('--expose-gc');
+  runInNewContext('gc')();
+
+  // The GC was not initially exposed, so let's hide it again.
+  if (isGarbageCollectorHidden) {
+    setFlagsFromString('--no-expose-gc');
+  }
+}
+
 // Inspired by https://github.com/mafintosh/why-is-node-running/blob/master/index.js
 // Extracted as we want to format the result ourselves
 export default function collectHandles(): HandleCollectionResult {
@@ -100,7 +118,14 @@ export default function collectHandles(): HandleCollectionResult {
 
   hook.enable();
 
-  return () => {
+  return async () => {
+    runGarbageCollector();
+
+    // wait some ticks to allow GC to run properly, see https://github.com/nodejs/node/issues/34636#issuecomment-669366235
+    for (let i = 0; i < 10; i++) {
+      await tick();
+    }
+
     hook.disable();
 
     // Get errors for every async resource still referenced at this moment

packages/jest-core/src/runJest.ts

@@ -75,7 +75,7 @@ type ProcessResultOptions = Pick<
   outputStream: NodeJS.WriteStream;
 };
 
-const processResults = (
+const processResults = async (
   runResults: AggregatedResult,
   options: ProcessResultOptions,
 ) => {
@@ -89,7 +89,7 @@ const processResults = (
   } = options;
 
   if (collectHandles) {
-    runResults.openHandles = collectHandles();
+    runResults.openHandles = await collectHandles();
   } else {
     runResults.openHandles = [];
   }
@@ -278,7 +278,7 @@ export default async function runJest({
     await runGlobalHook({allTests, globalConfig, moduleName: 'globalTeardown'});
   }
 
-  processResults(results, {
+  await processResults(results, {
     collectHandles,
     json: globalConfig.json,
     onComplete,