Works a little bit like `Array.prototype.forEach()`, but uses `process.nextTick` to allow other processes to execute. NOTE. This isn't meant to be practical; if you use this in production code you're probably doing it wrong.

nonBlockingForEach.js

/**
 * Allow other processes to execute while iterating over 
 * an array. Useful for large arrays, or long-running processing
 *
 * @param {Function} fn    iterator fed each element of the array.
 * @param {Function} next  executed when done
 */
Array.prototype.nonBlockingForEach = function(fn, next) {
  var arr = this;
  var i = 0;
  var len = arr.length;
  function iter() {
    if (i < len) {
      fn(arr[i]);
      i++;
      process.nextTick(iter);
    } else {
      next();
    }
  }
  iter();
};

@gabrieledarrigo, the documentation for process.nextTick says

Note: the nextTick queue is completely drained on each pass of the event loop before additional I/O is processed. As a result, recursively setting nextTick callbacks will block any I/O from happening, just like a while(true); loop.

This is exactly what this function is doing so no wonder your express end points are not responding.

Use setImmediate instead of process.nextTick