promise scheduler (gcanti/fetch-optimizer)

experiment.js

// run with: node --harmony experiment.js
var R = require('ramda');

var PromiseScheduler = (function() {
  function PromiseScheduler() {
    this.nodes = {};
  }

  PromiseScheduler.prototype.add = function(id, fetcher, dependencies) {
    this.nodes[id] = {
      fetcher: fetcher,
      dependencies: dependencies
    }
    return this;
  }

  // gets maximal elements
  PromiseScheduler.prototype.maximal = function() {
    var that = this;
    return Object.keys(this.nodes).filter(id =>
      Object.keys(that.nodes).every(otherId =>
        that.nodes[otherId].dependencies.indexOf(id) == -1));
  }

  // ensures all dependencies of all `nodes` have been started and
  // then sets `fetcher` for all `nodes` to be run at completion of
  // all its dependencies
  //
  // we mutate `this.nodes` for memoization (`.promise` is added when a promise has
  // been spawned for a fetcher)
  PromiseScheduler.prototype._internalSchedule = function(nodes) {
    var that = this;
    return nodes.map(function(id) {
      if (!that.nodes[id].promise) {
        that._internalSchedule(that.nodes[id].dependencies);
        var dependencyPromises = that.nodes[id].dependencies.map(depId =>
            that.nodes[depId].promise);
        that.nodes[id].promise = Promise.all(dependencyPromises).then(() =>
            that.nodes[id].fetcher());
      }
      return that.nodes[id].promise;
    });
  }

  PromiseScheduler.prototype.schedule = function() {
    return Promise.all(this._internalSchedule(this.maximal()));
  }

  return PromiseScheduler;
})();

var results = [];

function getFetcher(value, delay) {
  return function (res) {
    return new Promise(function (resolve) {
      console.log((Date.now() - start) + 'ms start ' + value);
      setTimeout(function () {
        results.push(value);
        resolve(value);
        console.log((Date.now() - start) + 'ms resolve ' + value);
      }, delay);
    });
  };
}

//   f2     f3
//     \   /  \
//       f1    f4
//         \  /
//          f5 <-- maximal element

const ps = new PromiseScheduler()
  .add('f1', getFetcher('f1', 50), ['f2', 'f3'])
  .add('f2', getFetcher('f2', 200), [])
  .add('f3', getFetcher('f3', 50), [])
  .add('f4', getFetcher('f4', 200), ['f3'])
  .add('f5', getFetcher('f5', 10), ['f1', 'f4']);

// optimal arrival times (spawining as soon as dependencies are available):
// f2: 200ms
// f3: 50ms
// f1: 250ms = max(f2, f3) + 50ms
// f4: 250ms = 50ms + 200ms
// f5: 260ms = max(f1, f4) + 10ms
//
// with poset chain:
// (f2, f3): 200ms = max(f2, f3)
// (f1, f4): 400ms = 200ms + max(f1, f4)
// (f5): 410ms = 400ms + 10ms

var start = Date.now();
ps.schedule().then(function(res) {
  console.log('result ' + results);
  console.log('res ' + res);
  var end = Date.now();
  console.log('done in ' + (end - start) + 'ms');
});