async await non-blocking example

async-await-non-blocking.md

async await non-blocking

In the context of the node process that handles multiple http requests, async await is non-blocking. Though in each request, async await will block.

See this example, calling the 2 endpoints /fast and /slow, /slow will respond after 3 seconds, you can call the /fast at the same time multiple times and you will get a response immediately.

index.js

// system imports
// 3rd party imports
const express = require('express')
// local imports

const app = express()
const port = 3000

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

app.get('/fast', (req, res) => {
  console.log('reached /fast')
  res.send('Hello World!')
})

app.get('/slow', async (req, res) => {
  const toSleep = 3000
  await sleep(toSleep)
  console.log('reached /slow')
  res.send(`After ${toSleep}ms, Hello World!`)
})

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`)
})

package.json

{
  "name": "async-wait-non-blocking",
  "version": "0.0.1",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  },
  "author": "kaizhang@duck.com",
  "license": "MIT",
  "dependencies": {
    "express": "^4.18.2"
  }
}