race2.js

/*

Results of a few runs:

$ node ./index.js
{
  "a": 1000
}
$ node ./index.js
{
  "a": 999,
  "ab": 1
}
$ node ./index.js
{
  "a": 998,
  "ab": 2
}
$ node ./index.js
{
  "a": 995,
  "ab": 5
}


*/


let {appendFile, readFile, writeFile} = require('fs')

let tally = {}
let globalDone = 0
let COUNT = 1000

for (let x = 0; x < COUNT; x++) {

  let path = './tmp/' + Math.random() + '.txt'

  // create file
  writeFile(path, 'a', () => {

  let result = ''
  let done = 0

  let checkDone = () => {
    done++
    if (done === 2) {
      globalDone++
      if (!(result in tally)) {
        tally[result] = 0
      }
      tally[result]++
    }
    if (globalDone === COUNT) {
      console.log(JSON.stringify(tally, null, 2))
    }
  }

  readFile(path, {encoding: 'utf8'}, (error, data) => {
    result = data
    checkDone()
  })

  appendFile(path, 'b', (error) => {
    checkDone()
  })
})
}