Optimize parameters of list thumbnail loader for MTP volume.

ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js

Index: ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js
diff --git a/ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js b/ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js
index adabbaa8a59fe3d2c239fc86fe9e535e5f779c83..3184679664eb411e75cb72c17d561d1cd1692c9c 100644
--- a/ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js
+++ b/ui/file_manager/file_manager/foreground/js/list_thumbnail_loader.js
@@ -12,6 +12,7 @@
  *
  * @param {!FileListModel} dataModel A file list model.
  * @param {!ThumbnailModel} thumbnailModel Thumbnail metadata model.
+ * @param {!VolumeManagerWrapper} volumeManager Volume manager.
  * @param {Function=} opt_thumbnailLoaderConstructor A constructor of thumbnail
  *     loader. This argument is used for testing.
  * @struct
@@ -20,60 +21,61 @@
  * @suppress {checkStructDictInheritance}
  */
 function ListThumbnailLoader(
-    dataModel, thumbnailModel, opt_thumbnailLoaderConstructor) {
+    dataModel, thumbnailModel, volumeManager, opt_thumbnailLoaderConstructor) {
   /**
-   * @type {!FileListModel}
-   * @private
+   * @private {!FileListModel}
    */
   this.dataModel_ = dataModel;
 
   /**
-   * @type {!ThumbnailModel}
-   * @private
+   * @private {!ThumbnailModel}
    */
   this.thumbnailModel_ = thumbnailModel;
 
   /**
+   * @private {!VolumeManagerWrapper}
+   */
+  this.volumeManager_ = volumeManager;
+
+  /**
    * Constructor of thumbnail loader.
-   * @type {!Function}
-   * @private
+   * @private {!Function}
    */
   this.thumbnailLoaderConstructor_ =
       opt_thumbnailLoaderConstructor || ThumbnailLoader;
 
   /**
-   * @type {Object<string, !ListThumbnailLoader.Task>}
-   * @private
+   * @private {Object<string, !ListThumbnailLoader.Task>}
    */
   this.active_ = {};
 
   /**
-   * @type {LRUCache<!ListThumbnailLoader.ThumbnailData>}
-   * @private
+   * @private {LRUCache<!ListThumbnailLoader.ThumbnailData>}
    */
   this.cache_ = new LRUCache(ListThumbnailLoader.CACHE_SIZE);
 
   /**
-   * @type {number}
-   * @private
+   * @private {number}
    */
   this.beginIndex_ = 0;
 
   /**
-   * @type {number}
-   * @private
+   * @private {number}
    */
   this.endIndex_ = 0;
 
   /**
    * Cursor.
-   * @type {number}
-   * @private
+   * @private {number}
    */
   this.cursor_ = 0;
 
-  // TODO(yawano): Change FileListModel to dispatch change event for file
-  // change, and change this class to handle it.
+  /**
+   * Current volume type.
+   * @private {?ListThumbnailLoader.VolumeType}
+   */
+  this.currentVolumeType_ = null;
+
   this.dataModel_.addEventListener('splice', this.onSplice_.bind(this));
   this.dataModel_.addEventListener('sorted', this.onSorted_.bind(this));
   this.dataModel_.addEventListener('change', this.onChange_.bind(this));
@@ -82,23 +84,64 @@ function ListThumbnailLoader(
 ListThumbnailLoader.prototype.__proto__ = cr.EventTarget.prototype;
 
 /**
- * Number of maximum active tasks.
+ * Cache size. Cache size must be larger than sum of high priority range size
+ * and number of prefetch tasks.
  * @const {number}
  */
-ListThumbnailLoader.NUM_OF_MAX_ACTIVE_TASKS = 10;
+ListThumbnailLoader.CACHE_SIZE = 500;
+
+/**
+ * Volume type for testing.
+ * @const {string}
+ */
+ListThumbnailLoader.TEST_VOLUME_TYPE = 'test_volume_type';
 
 /**
- * Number of prefetch requests.
- * @const {number}
+ * Number of maximum active tasks for testing.
+ * @type {number}
  */
-ListThumbnailLoader.NUM_OF_PREFETCH = 20;
+ListThumbnailLoader.numOfMaxActiveTasksForTest = 2;
 
 /**
- * Cache size. Cache size must be larger than sum of high priority range size
- * and number of prefetch tasks.
- * @const {number}
+ * @typedef {(VolumeManagerCommon.VolumeType|string)}
  */
-ListThumbnailLoader.CACHE_SIZE = 500;
+ListThumbnailLoader.VolumeType;
+
+/**
+ * Gets number of prefetch requests. This number changes based on current volume
+ * type.
+ * @return {number} Number of prefetch requests.
+ * @private
+ */
+ListThumbnailLoader.prototype.getNumOfPrefetch_ = function () {
+  switch (/** @type {?ListThumbnailLoader.VolumeType} */
+      (this.currentVolumeType_)) {
+    case VolumeManagerCommon.VolumeType.MTP:
+      return 0;
+    case ListThumbnailLoader.TEST_VOLUME_TYPE:
+      return 1;
+    default:
+      return 20;
+  }
+};
+
+/**
+ * Gets maximum number of active thumbnail fetch tasks. This number changes
+ * based on current volume type.
+ * @return {number} Maximum number of active thumbnail fetch tasks.
+ * @private
+ */
+ListThumbnailLoader.prototype.getNumOfMaxActiveTasks_ = function() {
+  switch (/** @type {?ListThumbnailLoader.VolumeType} */
+      (this.currentVolumeType_)) {
+    case VolumeManagerCommon.VolumeType.MTP:
+      return 1;
+    case ListThumbnailLoader.TEST_VOLUME_TYPE:
+      return ListThumbnailLoader.numOfMaxActiveTasksForTest;
+    default:
+      return 10;
+  }
+};
 
 /**
  * An event handler for splice event of data model. When list is changed, start
@@ -171,21 +214,24 @@ ListThumbnailLoader.prototype.getThumbnailFromCache = function(entry) {
 
 /**
  * Enqueues tasks if available.
- *
- * TODO(yawano): Make queueing for low priority thumbnail fetches more moderate
- * and smart.
  */
 ListThumbnailLoader.prototype.continue_ = function() {
-  // If tasks are running full or all items are scanned, do nothing.
-  if (!(Object.keys(this.active_).length <
-        ListThumbnailLoader.NUM_OF_MAX_ACTIVE_TASKS) ||
-      !(this.cursor_ < this.dataModel_.length) ||
-      !(this.cursor_ < this.endIndex_ + ListThumbnailLoader.NUM_OF_PREFETCH)) {
+  // If all items are scanned, do nothing.
+  if (!(this.cursor_ < this.dataModel_.length))
     return;
-  }
 
   var entry = /** @type {Entry} */ (this.dataModel_.item(this.cursor_));
 
+  // Check volume type for optimizing the parameters.
+  var volumeInfo = this.volumeManager_.getVolumeInfo(entry);
+  this.currentVolumeType_ = volumeInfo ? volumeInfo.volumeType : null;
+
+  // If tasks are running full or all items are scanned, do nothing.
+  if (!(Object.keys(this.active_).length < this.getNumOfMaxActiveTasks_()) ||
+      !(this.cursor_ < this.endIndex_ + this.getNumOfPrefetch_())) {
+    return;
+  }
+
   // If the entry is a directory, already in cache as valid or fetching, skip.
   var thumbnail = this.cache_.get(entry.toURL());
   if (entry.isDirectory ||