loop.js

var syscalls = require('syscalls');

var readables = {}; // {fd: callback}
var writables = {}; // {fd: callback}

exports.on = function(fd, event, callback) {
  if (event == 'read') {
    readables[fd] = callback;
  } else {
    writables[fd] = callback;
  }
}

exports.remove = function(fd, event) {
  if (event == 'read') {
    delete readables[fd];
  } else {
    delete writables[fd];
  }
};

var timers = [];
var timer = 0;
// loop.in(3, function () { ... })
exports.in = function(sec, callback) {
  timers.push({ timeout: timer + sec, callback: callback });
};

var nextTicks = [];
exports.nextTick = function(callback) {
  nextTicks.push(callback);
};

exports.run = function() {
  // Here the event LOOP!
  while (true) {
    for (var i=0; i < nextTicks.length; i++) {
      nextTicks[i]();
    };
    nextTicks = [];
    
    var fds = syscalls.select(Object.keys(readables), Object.keys(writables), [], 1);
    
    timer += 1;
    for (var i=0; i < timers.length; i++) {
      if (timers[i].timeout >= timer) {
        timers[i].callback();
        timers.splice(i, 1);
        i--;
      }
    };

    // fds = [
    //   [readables]
    //   [writables]
    //   [errors]
    // ]

    var readableFds = fds[0];
    var writableFds = fds[1];

    for (var i=0; i < readableFds.length; i++) {
      var fd = readableFds[i];
      var callback = readables[fd];
      callback();
    };
    for (var i=0; i < writableFds.length; i++) {
      var fd = writableFds[i];
      var callback = writables[fd];
      callback();
    };
  }
};