Simple demonstration with node on the limitations of being single threaded

node-single-thread-server.js

/**
 * Run this file with node, and point your browser to localhost:3000,
 * you'll get a simple "Hello world." back immediately.
 * 
 * If you go to localhost:3000/wait though, it will wait for 10 seconds
 * before getting the "Hello world." - this is a CPU block, not an I/O.
 *
 * That means it blocks every other request to the server as well (you can
 * test by going to localhost:3000 in another browser tab while you wait
 * for the localhost:3000/wait).
 */
var http = require('http');

function cpuJob(duration) {
  var startTime = new Date().getTime();
  while (new Date().getTime() - startTime < duration) {
    // do nothing...
  }
}

var server = http.createServer(function (req, res) {
    if (req.url === '/wait') {
      cpuJob(10000);
    }
    res.end("Hello world.");
});

server.listen(3000);