nonconcurrent.js

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var dns = require("dns");
var count = 0;

var gotResponse = true;
setInterval(function () {
  var cnt = ++count;
  if (gotResponse) {
    gotResponse = false;
    console.time("dnslookup"+ cnt);
    dns.lookup("carbon.hostedgraphite.com",4,function(err, address, family) {
        console.timeEnd("dnslookup"+ cnt);
        gotResponse = true;
      });
  }
},1);

testdns.js

var dns = require("dns");
var count = 0;

setInterval(function () {
  var cnt = ++count;
  console.time("dnslookup"+ cnt);
  dns.lookup("carbon.hostedgraphite.com",4,function(err, address, family) {
      console.timeEnd("dnslookup"+ cnt);
    });
},1);