Showing stalled file reads because of `dns.lookup`

dnsCaller.js

var dns = require("dns");
var http = require("http");
var fs = require("fs");
var net = require("net");

dns.setServers(["127.0.0.1"]);

var makeCallLookup = function(cb) {
	dns.lookup("testSlow.com", cb);
}

var makeCallResolve = function(cb) {
	dns.resolve("testSlow.com", cb);
}

fs.writeFileSync("/tmp/testFile.txt", "Here is my content");

setInterval(function() {
	fs.readFile("/tmp/testFile.txt", function(err, data) {
		if (err) { throw err; }
		
		console.log("file read", new Date());
	});
}, 100);

// pick a method to utilize
// var method = makeCallLookup;
var method = makeCallResolve;

setTimeout(function() {
	for(var i = 0; i < 4; i++) {
		(function() {
			method(function(err) {
				if (err) { throw err; }
				
				console.log("call done", i);
			});
		})(i);
	}
}, 1000);

dnsServer.js

var dns = require("dns");
var proxyDns = require("proxy-dns");

var server = new proxyDns.default({
	ttl : 600
});

server.use(function* (next) {
	console.log("got request", this.domain);
	
	if (this.domain === "testSlow.com") {
    // stall lookups to testSlow.com by 4s
		console.log("got slow request");
		yield new Promise((resolve, reject) => {
			setTimeout(() => {
				this.answers = ["127.0.0.1"];
				resolve();
			}, 4000);
		});
		yield next;
	} else {
    // resolve other calls using native behaviors
		yield new Promise((resolve, reject) => {
			dns.lookup(this.domain, function(err, ip) {
				if (err) {
					this.answers = [];
					return resolve();
				}
				
				this.answers = [ip];
				resolve();
			});
		});
		
		yield next;
	}
});

server.listen(53);

makeCallLookup.txt

When using method === makeCallLookup: The file reads which run every 100ms stall entirely for 4 seconds from :22 to :26.

file read 2017-01-13T17:28:21.222Z
file read 2017-01-13T17:28:21.301Z
file read 2017-01-13T17:28:21.401Z
file read 2017-01-13T17:28:21.502Z
file read 2017-01-13T17:28:21.603Z
file read 2017-01-13T17:28:21.705Z
file read 2017-01-13T17:28:21.805Z
file read 2017-01-13T17:28:21.906Z
file read 2017-01-13T17:28:22.006Z
call done 4
call done 4
call done 4
call done 4
file read 2017-01-13T17:28:26.158Z
file read 2017-01-13T17:28:26.158Z
file read 2017-01-13T17:28:26.158Z
file read 2017-01-13T17:28:26.158Z
file read 2017-01-13T17:28:26.158Z
file read 2017-01-13T17:28:26.159Z
file read 2017-01-13T17:28:26.159Z

makeCallResolve.txt

When using method === makeCallResolve: There is no delay to the fs calls at all.

file read 2017-01-13T17:36:44.093Z
file read 2017-01-13T17:36:44.173Z
file read 2017-01-13T17:36:44.274Z
file read 2017-01-13T17:36:44.375Z
file read 2017-01-13T17:36:44.477Z
file read 2017-01-13T17:36:44.578Z
file read 2017-01-13T17:36:44.679Z
file read 2017-01-13T17:36:44.779Z
file read 2017-01-13T17:36:44.879Z
file read 2017-01-13T17:36:44.980Z
file read 2017-01-13T17:36:45.081Z
file read 2017-01-13T17:36:45.182Z
file read 2017-01-13T17:36:45.283Z
file read 2017-01-13T17:36:45.385Z
file read 2017-01-13T17:36:45.485Z
file read 2017-01-13T17:36:45.586Z
file read 2017-01-13T17:36:45.686Z
file read 2017-01-13T17:36:45.786Z
file read 2017-01-13T17:36:45.887Z
file read 2017-01-13T17:36:45.987Z
file read 2017-01-13T17:36:46.087Z
file read 2017-01-13T17:36:46.188Z
file read 2017-01-13T17:36:46.289Z
file read 2017-01-13T17:36:46.390Z
file read 2017-01-13T17:36:46.491Z
file read 2017-01-13T17:36:46.592Z
file read 2017-01-13T17:36:46.693Z
file read 2017-01-13T17:36:46.794Z
file read 2017-01-13T17:36:46.895Z
file read 2017-01-13T17:36:46.996Z
file read 2017-01-13T17:36:47.097Z
file read 2017-01-13T17:36:47.198Z
file read 2017-01-13T17:36:47.299Z
file read 2017-01-13T17:36:47.400Z
file read 2017-01-13T17:36:47.501Z
file read 2017-01-13T17:36:47.602Z
file read 2017-01-13T17:36:47.702Z
file read 2017-01-13T17:36:47.802Z
file read 2017-01-13T17:36:47.903Z
file read 2017-01-13T17:36:48.004Z
file read 2017-01-13T17:36:48.105Z
file read 2017-01-13T17:36:48.206Z
file read 2017-01-13T17:36:48.308Z
file read 2017-01-13T17:36:48.408Z
file read 2017-01-13T17:36:48.509Z
file read 2017-01-13T17:36:48.610Z
file read 2017-01-13T17:36:48.711Z
file read 2017-01-13T17:36:48.812Z
file read 2017-01-13T17:36:48.914Z
call done 4
call done 4
call done 4
call done 4
file read 2017-01-13T17:36:49.015Z
file read 2017-01-13T17:36:49.115Z
file read 2017-01-13T17:36:49.216Z
file read 2017-01-13T17:36:49.318Z
file read 2017-01-13T17:36:49.418Z
file read 2017-01-13T17:36:49.518Z
file read 2017-01-13T17:36:49.619Z
file read 2017-01-13T17:36:49.720Z
file read 2017-01-13T17:36:49.821Z
file read 2017-01-13T17:36:49.922Z
file read 2017-01-13T17:36:50.023Z
file read 2017-01-13T17:36:50.124Z
file read 2017-01-13T17:36:50.225Z
file read 2017-01-13T17:36:50.326Z
file read 2017-01-13T17:36:50.426Z
file read 2017-01-13T17:36:50.526Z
file read 2017-01-13T17:36:50.627Z
file read 2017-01-13T17:36:50.728Z
file read 2017-01-13T17:36:50.829Z