node.js - learnyounode #9 juggling async, can official solution break? -

so learning node.js right , have done multitasking before , concept async , multitasking have many similar isses, brings me question.

the official solution problem is:

  var http = require('http')     var bl = require('bl')     var results = []     var count = 0      function printresults () {       (var = 0; < 3; i++)         console.log(results[i])     }      function httpget (index) {       http.get(process.argv[2 + index], function (response) {         response.pipe(bl(function (err, data) {           if (err)             return console.error(err)            results[index] = data.tostring()           //area of interest start           count++            if (count == 3)             printresults()           //area of interest end         }))       })     }      (var = 0; < 3; i++)       httpget(i) 

notice part in 'area of interest' comments. not possible race condition occur here causing printresults function called multiple times?

for example, 3 'end' callbacks come simultaneously, each executes count++ 1 after other (so count == 3 check has not happened yet on callback count has been increment thrice) each of them check count == 3 condition, true calling printresults thrice

is possible , official solution flawed or misunderstanding concepts?

no, race condition not problem code. callbacks run in single thread. not run @ once in parallel. run in series.

for more information on how callbacks queued , why there no race condition in code, may choose watch a great video philip roberts called "what heck event loop anyway?".