ensure that the function's first invocation will be exclusive

initGuard.js

var fs = require('fs');

function guardInit (init) {
  var delayedCalls = [];
  var status = 'not initialized';

  return function () {
    if (status == 'initializing')
      return delayedCalls.push(arguments);
    if (status == 'initialized')
      return init.apply(null, arguments);

    if (status != 'not initialized')
      throw "你他么逗我";

    status = 'initializing';

    arguments = Array.prototype.slice.call(arguments);
    
    var userCallback = arguments[arguments.length - 1];
    if (typeof userCallback == 'function')
      arguments = arguments.slice(0, -1);
    else
      userCallback = function () {};

    arguments.push(function () {
      userCallback.apply(null, arguments);
      status = 'initialized';

      delayedCalls.forEach(function (delayedArgs) {
        init.apply(null, delayedArgs);
      });
    });

    init.apply(null, arguments);
  };
}

var dataset = ['/Users/LiuMS'];

var readdir = guardInit(function (id, callback) {
  var path = dataset[id];
  console.log('干我咯', path);
  fs.readdir(path, callback);
});

for (var i = 0; i < 5; i ++) {
  readdir(i, function (err, res) {
    if (err)
      throw err;
    res = res.map(function (name) { return dataset[0] + '/' + name});
    console.log('WOCAO', dataset, res);
    dataset = dataset.concat(res);
    console.log('WOCAOCAO', dataset);
  });
}

console.log(dataset);