lockedStore.js

gistfile1.js

LockedStore = function() { };

LockedStore.prototype = {
  table: [],

  /**
   * index - Index of the value to check out.
   * callback(value, fn) - Fired when a lock is acquired on the requested value. First
   *   parameter is the requested value, second parameter is a callback that must be
   *   fired to check the value back in and expects the new value as a single parameter.
   */
  checkOut: function(index, callback) {
    if (!this.table[index])
      this.table[index] = { locked: false, pending: [callback], data: null };

    var obj = this.table[index];
    if (obj.locked)
      return obj.pending.push(callback);

    var doCheckOut = function() {
      obj.locked = true;
      var curCallback = obj.pending.shift();
      curCallback(obj.data, function(newVal) {
        obj.data = newVal;
        obj.locked = false;

        if (obj.pending.length)
          doCheckOut();
      });
    };

    doCheckOut();
  },
};