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   1  /**
   2   * @provides javelin-router
   3   * @requires javelin-install
   4   *           javelin-util
   5   * @javelin
   6   */
   7  
   8  /**
   9   * Route requests. Primarily, this class provides a quality-of-service
  10   * priority queue so large numbers of background loading tasks don't block
  11   * interactive requests.
  12   */
  13  JX.install('Router', {
  14  
  15    construct: function() {
  16      this._queue = [];
  17    },
  18  
  19    events: ['queue', 'start', 'done'],
  20  
  21    members: {
  22      _queue: null,
  23      _active: 0,
  24      _limit: 5,
  25  
  26      queue: function(routable) {
  27        this._queue.push(routable);
  28  
  29        this.invoke('queue', routable);
  30        this._update();
  31      },
  32  
  33      getRoutableByKey: function(key) {
  34        for (var ii = 0; ii < this._queue.length; ii++) {
  35          if (this._queue[ii].getKey() == key) {
  36            return this._queue[ii];
  37          }
  38        }
  39        return null;
  40      },
  41  
  42      /**
  43       * Start new requests if we have slots free for them.
  44       */
  45      _update: function() {
  46        var active = this._active;
  47        var limit = this._limit;
  48  
  49        if (active >= limit) {
  50          // If we're already at the request limit, we can't add any more
  51          // requests.
  52          return;
  53        }
  54  
  55        // If we only have one free slot, we reserve it for a request with
  56        // at least priority 1000.
  57        var minimum;
  58        if ((active + 1) == limit) {
  59          minimum = 1000;
  60        } else {
  61          minimum = 0;
  62        }
  63  
  64        var idx = this._getNextRoutable(minimum);
  65        if (idx === null) {
  66          return;
  67        }
  68  
  69        var routable = this._queue[idx];
  70        this._queue.splice(idx, 1);
  71  
  72  
  73        routable.listen('done', JX.bind(this, this._done, routable));
  74  
  75        this._active++;
  76        routable.start();
  77        this.invoke('start', routable);
  78  
  79        this._update();
  80      },
  81  
  82      _done: function(routable) {
  83        this._active--;
  84        this.invoke('done', routable);
  85  
  86        this._update();
  87      },
  88  
  89      _getNextRoutable: function(minimum) {
  90        var best = (minimum - 1);
  91  
  92        var routable = null;
  93        for (var ii = 0; ii < this._queue.length; ii++) {
  94          var priority = this._queue[ii].getPriority();
  95          if (priority > best) {
  96            best = priority;
  97            routable = ii;
  98          }
  99        }
 100  
 101        return routable;
 102      }
 103  
 104    },
 105  
 106    statics: {
 107      _instance: null,
 108      getInstance: function() {
 109        if (!JX.Router._instance) {
 110          JX.Router._instance = new JX.Router();
 111        }
 112        return JX.Router._instance;
 113      }
 114    }
 115  });