// FullParallel businessLogichronous engine
function fullParallel(callbacks, last) {
  var results = [];
  var result_count = 0;

  callbacks.forEach(function(callback, index) {

    callback( function() {
      results[index] = Array.prototype.slice.call(arguments);
      result_count++;

      if(result_count == callbacks.length) { // the termination guard is checked in the businessLogic!!
        last(results);
      }
    });

  });
}

// Example task (business logic). Despite the name, this is a normal function
function businessLogic(arg, callback) {
  var delay = Math.floor(Math.random() * 5 + 1) * 100; // random ms
  console.log('businessLogic with \''+arg+'\', return in '+delay+' ms');
  setTimeout(function() { callback(arg * 2); }, delay);
}

function end(results) { console.log('Done', results); } 

var theCallbacks = [
  function(next) { 
    businessLogic(1, next); 
  },
  function(next) { businessLogic(2, next); },
  function(next) { businessLogic(3, next); },
  function(next) { businessLogic(4, next); },
  function(next) { businessLogic(5, next); },
  function(next) { businessLogic(6, next); }
];

fullParallel(theCallbacks, end);