Javascript function to create heapsnapshot and heapprofile

heap-recorder.js

'use strict';

const v8Profiler = require('v8-profiler-next');
const fs = require('fs');
const fsPromises = require('fs').promises;
const { join } = require('path');
const appLogger = require('../logger');

const wait = (timeMS) => new Promise((res) => setTimeout(res, timeMS));
const snapshotsFolder = join(__dirname, '..', 'heap-snapshots');

// Use synchronous methods for directory check and creation
if (!fs.existsSync(snapshotsFolder)) {
  fs.mkdirSync(snapshotsFolder);
}

const THIRTY_SECONDS_IN_MILLISECONDS = 30_000;

/**
 * Takes a heap snapshot with minimal impact on the main thread
 * @returns {Promise<void>} Path to the saved snapshot file
 */
async function createHeapSnapshot() {
  try {
    appLogger.info('snapshotHeap recording started...');
    const filename = join(snapshotsFolder, `${Date.now().toString()}.heapsnapshot`);

    // Take the snapshot - This operation blocks the main thread.
    const snapshot = v8Profiler.takeSnapshot();
    const transform = snapshot.export();

    const writeStream = fs.createWriteStream(filename, { flags: 'w' });
    transform.pipe(writeStream);

    transform.on('finish', () => {
      snapshot.delete();
      appLogger.info(`snapshot heap recording completed: ${filename}`);
    });

    transform.on('error', (err) => {
      appLogger.withError(err).error('error taking heap snapshot');
    });
  } catch (err) {
    appLogger.withError(err).error('error in creating heap snapshot');
  }
}

/**
 * Creates a heap profile over a specified duration
 * @param {number} timeMs - Duration in milliseconds to profile
 * @returns {Promise<void>} Path to the saved profile file
 */
async function createHeapProfile(timeMs = THIRTY_SECONDS_IN_MILLISECONDS) {
  try {
    appLogger.info(`heap profiling for ${timeMs / 1000} recording started...`);
    const filename = join(snapshotsFolder, `${Date.now().toString()}.heapprofile`);

    // Start profiling
    v8Profiler.startSamplingHeapProfiling();

    // Wait for specified duration
    await wait(timeMs);

    // Stop profiling and save results
    const profile = v8Profiler.stopSamplingHeapProfiling();

    try {
      await fsPromises.writeFile(filename, JSON.stringify(profile));
      appLogger.info(`heap profile recording completed: ${filename}`);
    } catch (writeErr) {
      appLogger.withError(writeErr).error('error writing heap profile to file');
    }
  } catch (err) {
    appLogger.withError(err).error('error in creating heap profile');
  }
}

module.exports = {
  createHeapSnapshot,
  createHeapProfile,
};