a proper fibonacci server in node. it will light up all your cores.

fib.js

var os = require('os');
var http = require('http')
var fork = require('child_process').fork;

function fib(n) {
  if (n < 2) {
    return 1;
  } else {
    return fib(n - 2) + fib(n - 1);
  }
}

if (process.argv[2] == 'fib') {
  process.on('message', function(m) {
    process.send({ result: fib(m.input) });
  });
} else {
  var busyChildren = 0;
  var freeChildren = [];
  var reqQueue = [];
  var maxChildren = os.cpus().length;
  console.log('max children: ' + maxChildren);

  function getChild(callback) {
    console.log('free: ' + freeChildren.length + ', busy: ' + busyChildren +
      ', req: ' + reqQueue.length);
    if (freeChildren.length === 0) {
      if (freeChildren.length + busyChildren >= maxChildren) {
        reqQueue.push(callback);
      } else {
        // spawn new child
        console.log('spawn new child');
        var ch = fork(__filename, [ 'fib' ]);
        busyChildren++;
        callback(null, ch);
      }
    } else {
      // hand out one child
      var ch = freeChildren.pop();
      busyChildren++;
      callback(null, ch)
    }
  }

  function returnChild(child) {
    busyChildren--;
    freeChildren.push(child);
    console.log('free: ' + freeChildren.length + ', busy: ' + busyChildren +
      ', req: ' + reqQueue.length);
    if (reqQueue.length > 0) {
      getChild(function(err, ch) {
        if (err) return;
        var rcb = reqQueue.pop();
        process.nextTick(function() { rcb(null, ch); });
      });
    }
  }

  var server = http.createServer(function(req, res) {
    getChild(function(err, child) {
      if (err) {
        res.writeHead(500);
        res.end('Could not get child.\n');
        return;
      }
      child.once('message', function(m) {
        res.writeHead(200);
        res.end(m.result + "\n");
        returnChild(child);
      });
      child.send({ input: 40 });
    });
  });
  server.listen(8000);
  console.log("server online at http://localhost:8000/")
}