loop-async-leak.js

'use strict';

/* global gc */

const RESULT_OBJECT = new Array(128).fill(0).map(x => ~~(Math.random() * 128));

const STREAM_LENGTH = 10;
const SUITE_SIZE = 10000;

function deepCloneInner(obj) {
	/* Some heavy sync operation */
	if (obj === null || typeof obj !== 'object') return obj;
	if (Array.isArray(obj)) return obj.map(prop => deepCloneInner(prop));
	const clone = Object.create(Object.getPrototypeOf(obj));
	for (const key of Object.keys(obj)) {
		clone[key] = deepCloneInner(obj[key]);
	}
	return clone;
}

function deepCloneSync(obj) {
	return deepCloneInner(obj);
}

async function deepClone(obj) {
	return deepCloneInner(obj);
}

async function deepCloneNextTick(obj) {
	return new Promise((resolve, reject) => {
		process.nextTick(() => resolve(deepCloneInner(obj)));
	});
}

async function deepCloneSetImmediate(obj) {
	return new Promise((resolve, reject) => {
		setImmediate(() => resolve(deepCloneInner(obj)));
	});
}

async function deepCloneAwait(obj) {
	await 'ayuwoki';
	return deepCloneInner(obj);
}

const MY_STREAM = {
	iterations: 0,
	async read() {
		if (++this.iterations % STREAM_LENGTH === 0) {
			return null;
		}

		/*
		 * Using deepCloneSync() causes a leak of Promises in Node 10.15.3 (V8 6.8.275.32-node.51),
		 * but it doesn't leak in Node 8.15.1 (V8 6.2.414.75)
		 *
		 * Leak also confirmed (Increase SUITE_SIZE x10) in:
		 *   node 12.0.0-nightly20190331bb98f27181, v8 7.4.288.13-node.13
		 *   node 12.0.0-v8-canary201903313c649ecee6, v8 7.5.149-node.0
		 *   
		 */
		return deepCloneSync(RESULT_OBJECT);
		// return deepClone(RESULT_OBJECT);
		// return deepCloneNextTick(RESULT_OBJECT);
		// return deepCloneSetImmediate(RESULT_OBJECT);
		// return deepCloneAwait(RESULT_OBJECT);
	},
};

const ENV = {
	iterations: 0,
	getNextGameParameters() {
		if (++this.iterations % SUITE_SIZE === 0) {
			return null;
		}
		return this.iterations % 2 ? 'arg1' : 'arg2';
	},
};

async function runGame(logOutput) {
	let chunk;
	let x = Promise.resolve();

	// Changing this to chunk = await MY_STREAM.read() removes the leak.
	while ((chunk = await Promise.race([MY_STREAM.read(), x]))) {
		if (logOutput) console.log(chunk);
	}
}

async function runSuite() {
	let parameters;
	let iterations = 0;
	while ((parameters = ENV.getNextGameParameters())) {
		await runGame().catch(err => {
			console.error(`Error for parameters ${parameters}\n${err.stack}`);
		});

		// Uncommenting fixes the leak (Node.js only)
		/*
		if (iterations++ % 50 === 0) {
			await new Promise(resolve => setImmediate(resolve));
		}
		//*/
	}
}

(async () => {
	await runSuite();
})();