remoting/webapp/stats_accumulator.js

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 /**
   6  * @fileoverview
   7  * The webapp reads the plugin's connection statistics frequently (once per
   8  * second). It logs statistics to the server less frequently, to keep
   9  * bandwidth and storage costs down. This class bridges that gap, by
  10  * accumulating high-frequency numeric data, and providing statistics
  11  * summarising that data.
  12  */
  13
  14 'use strict';
  15
  16 /** @suppress {duplicate} */
  17 var remoting = remoting || {};
  18
  19 /**
  20  * @constructor
  21  */
  22 remoting.StatsAccumulator = function() {
  23   /**
  24    * A map from names to lists of values.
  25    * @private
  26    * @type Object.<string, Array.<number>>
  27    */
  28   this.valueLists_ = {};
  29
  30   /**
  31    * The first time, after this object was most recently initialized or emptied,
  32    * at which a value was added to this object.
  33    * @private
  34    * @type {?number}
  35    */
  36   this.timeOfFirstValue_ = null;
  37 };
  38
  39 /**
  40  * Adds values to this object.
  41  *
  42  * @param {Object.<string, number>} newValues
  43  */
  44 remoting.StatsAccumulator.prototype.add = function(newValues) {
  45   for (var key in newValues) {
  46     this.getValueList(key).push(newValues[key]);
  47   }
  48   if (!this.timeOfFirstValue_) {
  49     this.timeOfFirstValue_ = new Date().getTime();
  50   }
  51 };
  52
  53 /**
  54  * Empties this object.
  55  */
  56 remoting.StatsAccumulator.prototype.empty = function() {
  57   this.valueLists_ = {};
  58   this.timeOfFirstValue_ = null;
  59 };
  60
  61 /**
  62  * Gets the number of milliseconds since the first value was added to this
  63  * object, after this object was most recently initialized or emptied.
  64  *
  65  * @return {number} milliseconds since the first value
  66  */
  67 remoting.StatsAccumulator.prototype.getTimeSinceFirstValue = function() {
  68   if (!this.timeOfFirstValue_) {
  69     return 0;
  70   }
  71   return new Date().getTime() - this.timeOfFirstValue_;
  72 };
  73
  74 /**
  75  * Calculates the mean of the values for a given key.
  76  *
  77  * @param {string} key
  78  * @return {number} the mean of the values for that key
  79  */
  80 remoting.StatsAccumulator.prototype.calcMean = function(key) {
  81   /**
  82    * @param {Array.<number>} values
  83    * @return {number}
  84    */
  85   var calcMean = function(values) {
  86     if (values.length == 0) {
  87       return 0.0;
  88     }
  89     var sum = 0;
  90     for (var i = 0; i < values.length; i++) {
  91       sum += values[i];
  92     }
  93     return sum / values.length;
  94   };
  95   return this.map(key, calcMean);
  96 };
  97
  98 /**
  99  * Applies a given map to the list of values for a given key.
 100  *
 101  * @param {string} key
 102  * @param {function(Array.<number>): number} map
 103  * @return {number} the result of applying that map to the list of values for
 104  *     that key
 105  */
 106 remoting.StatsAccumulator.prototype.map = function(key, map) {
 107   return map(this.getValueList(key));
 108 };
 109
 110 /**
 111  * Gets the list of values for a given key.
 112  * If this object contains no values for that key, then this routine creates
 113  * an empty list, stores it in this object, and returns it.
 114  *
 115  * @private
 116  * @param {string} key
 117  * @return {Array.<number>} the list of values for that key
 118  */
 119 remoting.StatsAccumulator.prototype.getValueList = function(key) {
 120   var valueList = this.valueLists_[key];
 121   if (!valueList) {
 122     valueList = [];
 123     this.valueLists_[key] = valueList;
 124   }
 125   return valueList;
 126 };