How to calculate the execution time of an async function in JavaScript?

Question

I would like to calculate how long an async function (async/await) is taking in JavaScript.

One could do:

const asyncFunc =         


        

Answer 1

The problem we have

process.nextTick(() => {/* hang 100ms */})
const asyncFunc = async () => {/* hang 10ms */}
const t0 = /* timestamp */
asyncFunc().then(() => {
  const t1 = /* timestamp */
  const timeUsed = t1 - t0 /* 110ms because of nextTick */
  /* WANTED: timeUsed = 10ms */
})

A solution (idea)

const AH = require('async_hooks')
const hook = /* AH.createHook for
   1. Find async scopes that asycnFunc involves ... SCOPES
      (by handling 'init' hook)
   2. Record time spending on these SCOPES ... RECORDS 
      (by handling 'before' & 'after' hook) */
hook.enable()
asyncFunc().then(() => {
  hook.disable()
  const timeUsed = /* process RECORDS */
})

But this wont capture the very first sync operation; i.e. Suppose asyncFunc as below, $1$ wont add to SCOPES(as it is sync op, async_hooks wont init new async scope) and then never add time record to RECORDS

hook.enable()
/* A */
(async function asyncFunc () { /* B */
  /* hang 10ms; usually for init contants etc ... $1$ */ 
  /* from async_hooks POV, scope A === scope B) */
  await /* async scope */
}).then(..)

To record those sync ops, a simple solution is to force them to run in a new ascyn scope, by wrapping into a setTimeout. This extra stuff does take time to run, ignore it because the value is very small

hook.enable()
/* force async_hook to 'init' new async scope */
setTimeout(() => { 
   const t0 = /* timestamp */
   asyncFunc()
    .then(()=>{hook.disable()})
    .then(()=>{
      const timeUsed = /* process RECORDS */
    })
   const t1 = /* timestamp */
   t1 - t0 /* ~0; note that 2 `then` callbacks will not run for now */ 
}, 1)

Note that the solution is to 'measure time spent on sync ops which the async function involves', the async ops e.g. timeout idle will not count, e.g.

async () => {
  /* hang 10ms; count*/
  await new Promise(resolve => {
    setTimeout(() => {
      /* hang 10ms; count */
      resolve()
    }, 800/* NOT count*/)
  }
  /* hang 10ms; count*/
}
// measurement takes 800ms to run
// timeUsed for asynFunc is 30ms

---

Last, I think it maybe possible to measure async function in a way that includes both sync & async ops(e.g. 800ms can be determined) because async_hooks does provide detail of scheduling, e.g. setTimeout(f, ms), async_hooks will init an async scope of "Timeout" type, the scheduling detail, ms, can be found in resource._idleTimeout at init(,,,resource) hook

---

Demo(tested on nodejs v8.4.0)

// measure.js
const { writeSync } = require('fs')
const { createHook } = require('async_hooks')

class Stack {
  constructor() {
    this._array = []
  }
  push(x) { return this._array.push(x) }
  peek() { return this._array[this._array.length - 1] }
  pop() { return this._array.pop() }
  get is_not_empty() { return this._array.length > 0 }
}

class Timer {
  constructor() {
    this._records = new Map/* of {start:number, end:number} */
  }
  starts(scope) {
    const detail =
      this._records.set(scope, {
        start: this.timestamp(),
        end: -1,
      })
  }
  ends(scope) {
    this._records.get(scope).end = this.timestamp()
  }
  timestamp() {
    return Date.now()
  }
  timediff(t0, t1) {
    return Math.abs(t0 - t1)
  }
  report(scopes, detail) {
    let tSyncOnly = 0
    let tSyncAsync = 0
    for (const [scope, { start, end }] of this._records)
      if (scopes.has(scope))
        if (~end) {
          tSyncOnly += end - start
          tSyncAsync += end - start
          const { type, offset } = detail.get(scope)
          if (type === "Timeout")
            tSyncAsync += offset
          writeSync(1, `async scope ${scope} \t... ${end - start}ms \n`)
        }
    return { tSyncOnly, tSyncAsync }
  }
}

async function measure(asyncFn) {
  const stack = new Stack
  const scopes = new Set
  const timer = new Timer
  const detail = new Map
  const hook = createHook({
    init(scope, type, parent, resource) {
      if (type === 'TIMERWRAP') return
      scopes.add(scope)
      detail.set(scope, {
        type: type,
        offset: type === 'Timeout' ? resource._idleTimeout : 0
      })
    },
    before(scope) {
      if (stack.is_not_empty) timer.ends(stack.peek())
      stack.push(scope)
      timer.starts(scope)
    },
    after() {
      timer.ends(stack.pop())
    }
  })

  // Force to create a new async scope by wrapping asyncFn in setTimeout,
  // st sync part of asyncFn() is a async op from async_hooks POV.
  // The extra async scope also take time to run which should not be count
  return await new Promise(r => {
    hook.enable()
    setTimeout(() => {
      asyncFn()
        .then(() => hook.disable())
        .then(() => r(timer.report(scopes, detail)))
        .catch(console.error)
    }, 1)
  })
}

Test

// arrange
const hang = (ms) => {
  const t0 = Date.now()
  while (Date.now() - t0 < ms) { }
}
const asyncFunc = async () => {
  hang(16)                           // 16
  try {
    await new Promise(r => {
      hang(16)                       // 16
      setTimeout(() => {
        hang(16)                     // 16
        r()
      }, 100)                        // 100
    })
    hang(16)                         // 16
  } catch (e) { }
  hang(16)                           // 16
}
// act
process.nextTick(() => hang(100))    // 100
measure(asyncFunc).then(report => {
  // inspect
  const { tSyncOnly, tSyncAsync } = report
  console.log(`
  ∑ Sync Ops       = ${tSyncOnly}ms \t (expected=${16 * 5})
  ∑ Sync&Async Ops = ${tSyncAsync}ms \t (expected=${16 * 5 + 100})
  `)
}).catch(e => {
  console.error(e)
})

Result

async scope 3   ... 38ms
async scope 14  ... 16ms
async scope 24  ... 0ms
async scope 17  ... 32ms

  ∑ Sync Ops       = 86ms       (expected=80)
  ∑ Sync&Async Ops = 187ms      (expected=180)