safe.js

/*jslint white: true, onevar: true, undef: true, nomen: true, eqeqeq: true,
  plusplus: true, bitwise: true, regexp: true, immed: true, maxlen: 78, 
  indent: 2 */

// Does short term (100ms) in-memory caching and combines concurrent requests
// to the same resource into a single callback group.
var Safe = module.exports = function Safe(fn, expires) {
  // return fn;
  var cache = {},
      queues = {};
  return function (key, callback) {
    if (key in cache) {
      return callback(null, cache[key]);
    }
    if (!(key in queues)) {
      queues[key] = [];
    }
    var queue = queues[key];
    if (queue.length > 0) {
      queue.push(callback);
      return;
    }
    queue[0] = callback;
    fn(key, function (err, data) {
      var results;
      for (var i = 0, l = queue.length; i < l; i += 1) {
        queue[i](err, data);
      }
      queue.length = 0;

      if (!err) {
        cache[key] = data;
        setTimeout(function () {
          delete cache[key];
        }, expires || 100);
      }
      
    });
  };
};