debugging-aid/inprogress/cpu.js

Experimental tools for debugging Node.js apps without pausing

// testcase
setInterval(function inint () {
  suspect()
}, 0)

function suspect () {
  const t0 = Date.now()
  while (t0 === Date.now()) {
    culprit()
  }
}

function culprit () {
  Math.sqrt(Math.pow(1111111111111, 22222))
}

// -----
const inspector = require('inspector')
const util = require('util')

const session = new inspector.Session()
const postAsync = util.promisify(session.post.bind(session))
const delay = (x = 10) => new Promise((re) => setTimeout(re, x))

let ranking = Object.create(null)
const rank = (key, hits) => {
  if (!ranking[key]) {
    ranking[key] = 0
  }
  ranking[key] += hits
}
function evaluateRanking () {
  const oldRanking = ranking
  const entries = Object.entries(oldRanking).sort((a, b) => {
    return b[1] - a[1]
  })
  ranking = entries
    .slice(0, Math.max(10, Math.ceil(entries.length / 10)))
    .reduce((acc, entry) => {
      acc[entry[0]] = entry[1]
      return acc
    }, Object.create(null))
  return ranking
}

session.connect()
session.post('Profiler.enable', () => {
  setInterval(oneProfile, 50)
  setInterval(() => {
    console.log(evaluateRanking())
  }, 10000)
  console.log('enable')
})

const signature = ({ url, functionName, lineNumber }) => {
  if (url) {
    return `${functionName}@${url}:${lineNumber}`
  } else {
    return functionName
  }
}

async function oneProfile () {
  try {
    await postAsync('Profiler.start')
    await delay(10)
    const result = await postAsync('Profiler.stop')
    result.profile.nodes.forEach((fn) => {
      if (fn.hitCount > 0 && fn.callFrame.functionName !== '(program)') {
        rank(signature(fn.callFrame), fn.hitCount)
      }
    })
  } catch (e) {
  }
}