concurrency - rolling average

app.js

var Promise     = require('bluebird');
var request     = Promise.promisify(require('request'));
var fs = require('fs');

global.Nylas = require('nylas').config({
  appId: '1',
  appSecret: '2',
  apiServer: 'https://api.nylas.com'
});

var MAX_COUNT = 5000;
var CONCURRENCY = 20;

var deltasProcessed = 0;
var deltasProcessedStart = 0;
var speedRollingAverage = 0;

var startStream = function (id)  {
  var Namespace = null;
  Nylas.with(<<NAMESPACE ID>>).namespaces.first({})
  .then(function(namespace) {
    Namespace = namespace;
    return Namespace.deltas.generateCursor(0);
  })
  .then(function(cursor) {
    console.log("Opening stream "+id);
    var DELTA_EXCLUDE_TYPES = ['contact', 'event', 'file', 'tag', 'thread'];
    var stream = Namespace.deltas.startStream(cursor, DELTA_EXCLUDE_TYPES);
    stream.on('data', function () {
      console.log("["+id+"] got data");
    });
    stream.on('delta', function(delta) {
      // Handle the new delta here.
      deltasProcessed += 1;
      if (Date.now() - deltasProcessedStart > 5000) {
        speedRollingAverage = speedRollingAverage * 0.8 + deltasProcessed * 0.2;
        console.log("Deltas in last 5000 msec: "+deltasProcessed + ". Rolling average of 5 samples: " +speedRollingAverage);
        deltasProcessed = 0;
        deltasProcessedStart = Date.now();
      }

    }).on('error', function(err) {
      // Handle errors here, such as by restarting the stream at the last cursor.
      console.error('Delta streaming error:', err);
    });
  });
};

// delayed so I can start the profiler
setTimeout(function() {
  startTime = new Date();
  console.log('Running '+CONCURRENCY+' assistants concurrently');
  for (var i = 0; i < CONCURRENCY; i++) {
    startStream(i);
  }
}, 5000);

// delay process exit forever so I can view the profile
setTimeout(function(){}, 20000000);