Merge pull request Flipboard#32 from darkyen/patch-1

LRU for image-cache

Author: Michael Johnston

lib/ImageCache.js

@@ -77,16 +77,65 @@ assign(Img.prototype, EventEmitter.prototype, {
 });
 
 var kInstancePoolLength = 300;
-var _instancePool = [];
 
-function getPooledImage (src) {
- for (var i=0, len=_instancePool.length; i < len; i++) {
- if (_instancePool[i].getOriginalSrc() === src) {
- return _instancePool[i];
+var _instancePool = {
+ length: 0,
+ // Keep all the nodes in memory.
+ elements: {
+ 
+ },
+ 
+ // Push with 0 frequency
+ push: function (hash, data) {
+ this.length++;
+ this.elements[hash] = {
+ hash: hash, // Helps identifying 
+ freq: 0,
+ data: data
+ };
+ },
+ 
+ get: function (path) {
+ var element = this.elements[path];
+ 
+ if( element ){
+ element.freq++;
+ return element.data;
+ }
+ 
+ return null;
+ },
+ 
+ // used to explicitely remove the path
+ removeElement: function (path) {
+ // Now almighty GC can claim this soul
+ var element = this.elements[path];
+ delete this.elements[path];
+ this.length--;
+ return element;
+ },
+ 
+ _reduceLeastUsed: function (least, currentHash) {
+ var current = _instancePool.elements[currentHash];
+ 
+ if( least.freq > current.freq ){
+ return current;
  }
+ 
+ return least;
+ },
+ 
+ popLeastUsed: function () {
+ var reducer = _instancePool._reduceLeastUsed;
+ var minUsed = Object.keys(this.elements).reduce(reducer, { freq: Infinity });
+ 
+ if( minUsed.hash ){
+ return this.removeElement(minUsed.hash); 
+ }
+ 
+ return null;
  }
- return null;
-}
+};
 
 var ImageCache = {
 
@@ -96,14 +145,14 @@ var ImageCache = {
  * @return {Img}
  */
  get: function (src) {
- var image = getPooledImage(src);
+ var image = _instancePool.get(src);
  if (!image) {
- // Simple FIFO queue
+ // Awesome LRU
  image = new Img(src);
  if (_instancePool.length >= kInstancePoolLength) {
- _instancePool.shift().destructor();
+ _instancePool.popLeastUsed().destructor();
  }
- _instancePool.push(image);
+  _instancePool.push(image.getOriginalSrc(), image);
  }
  return image;
  }