WidgetPreviewLoader concurrency issue / Caching improvement

1) Concurrency issue: unused bitmap was not properly synchronized
which caused concurrency issue. Hence, leading current widget tray
implementation to not use it. (a.k.a. cancel(false)).
Issue fixed and now using the unused bitmap pool.

2) Caching improvement: LoadedBitmap cache was a legacy support system
for the old widget tray implementation. On our latest implementation,
cache and recycled view is completely being managed by the recycler view.
Hence removed.

Change-Id: I843e6a286b676f283172f2c1ef5cbeed0a9fb17f

1 files changed, 20 insertions, 45 deletions

diff --git a/src/com/android/launcher3/WidgetPreviewLoader.java b/src/com/android/launcher3/WidgetPreviewLoader.java
index 5c3ed9272..412cbcd6d 100644
--- a/src/com/android/launcher3/WidgetPreviewLoader.java
+++ b/src/com/android/launcher3/WidgetPreviewLoader.java
@@ -34,7 +34,6 @@ import com.android.launcher3.util.ComponentKey;
 import com.android.launcher3.util.Thunk;
 import com.android.launcher3.widget.WidgetCell;
 
-import java.lang.ref.WeakReference;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -51,8 +50,13 @@ public class WidgetPreviewLoader {
     private static final float WIDGET_PREVIEW_ICON_PADDING_PERCENTAGE = 0.25f;
 
     private final HashMap<String, long[]> mPackageVersions = new HashMap<>();
-    private final HashMap<WidgetCacheKey, WeakReference<Bitmap>> mLoadedPreviews = new HashMap<>();
-    private Set<Bitmap> mUnusedBitmaps = Collections.newSetFromMap(new WeakHashMap<Bitmap, Boolean>());
+
+    /**
+     * Weak reference objects, do not prevent their referents from being made finalizable,
+     * finalized, and then reclaimed.
+     */
+    private Set<Bitmap> mUnusedBitmaps =
+            Collections.newSetFromMap(new WeakHashMap<Bitmap, Boolean>());
 
     private final Context mContext;
     private final IconCache mIconCache;
@@ -84,18 +88,9 @@ public class WidgetPreviewLoader {
         String size = previewWidth + "x" + previewHeight;
         WidgetCacheKey key = getObjectKey(o, size);
 
-        // Check if we have the preview loaded or not.
-        synchronized (mLoadedPreviews) {
-            WeakReference<Bitmap> ref = mLoadedPreviews.get(key);
-            if (ref != null && ref.get() != null) {
-                immediateResult[0] = ref.get();
-                return new PreviewLoadRequest(null, key);
-            }
-        }
-
         PreviewLoadTask task = new PreviewLoadTask(key, o, previewWidth, previewHeight, caller);
         task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
-        return new PreviewLoadRequest(task, key);
+        return new PreviewLoadRequest(task);
     }
 
     /**
@@ -192,22 +187,6 @@ public class WidgetPreviewLoader {
             mPackageVersions.remove(packageName);
         }
 
-        synchronized (mLoadedPreviews) {
-            Set<WidgetCacheKey> keysToRemove = new HashSet<>();
-            for (WidgetCacheKey key : mLoadedPreviews.keySet()) {
-                if (key.componentName.getPackageName().equals(packageName) && key.user.equals(user)) {
-                    keysToRemove.add(key);
-                }
-            }
-
-            for (WidgetCacheKey key : keysToRemove) {
-                WeakReference<Bitmap> req = mLoadedPreviews.remove(key);
-                if (req != null && req.get() != null) {
-                    mUnusedBitmaps.add(req.get());
-                }
-            }
-        }
-
         try {
             mDb.getWritableDatabase().delete(CacheDb.TABLE_NAME,
                     CacheDb.COLUMN_PACKAGE + " = ? AND " + CacheDb.COLUMN_USER + " = ?",
@@ -549,26 +528,25 @@ public class WidgetPreviewLoader {
     public class PreviewLoadRequest {
 
         private final PreviewLoadTask mTask;
-        private final WidgetCacheKey mKey;
 
-        public PreviewLoadRequest(PreviewLoadTask task, WidgetCacheKey key) {
+        public PreviewLoadRequest(PreviewLoadTask task) {
             mTask = task;
-            mKey = key;
         }
 
-        public void cancel(boolean recycleImage) {
+        public void cleanup() {
             if (mTask != null) {
                 mTask.cancel(true);
             }
 
-            if (recycleImage) {
-                synchronized(mLoadedPreviews) {
-                    WeakReference<Bitmap> result = mLoadedPreviews.remove(mKey);
-                    if (result != null && result.get() != null) {
-                        mUnusedBitmaps.add(result.get());
-                    }
-                }
+            if (mTask.mBitmap == null) {
+                return;
+            }
+
+            // The preview is no longer bound to any view, move it to {@link WeakReference} list.
+            synchronized(mUnusedBitmaps) {
+                mUnusedBitmaps.add(mTask.mBitmap);
             }
+            mTask.mBitmap = null;
         }
     }
 
@@ -579,6 +557,7 @@ public class WidgetPreviewLoader {
         private final int mPreviewHeight;
         private final int mPreviewWidth;
         private final WidgetCell mCaller;
+        private Bitmap mBitmap;
 
         PreviewLoadTask(WidgetCacheKey key, Object info, int previewWidth,
                 int previewHeight, WidgetCell caller) {
@@ -597,7 +576,6 @@ public class WidgetPreviewLoader {
         protected Bitmap doInBackground(Void... params) {
             Bitmap unusedBitmap = null;
 
-            // TODO(hyunyoungs): Figure out why this path causes concurrency issue.
             synchronized (mUnusedBitmaps) {
                 // Check if we can use a bitmap
                 for (Bitmap candidate : mUnusedBitmaps) {
@@ -638,10 +616,7 @@ public class WidgetPreviewLoader {
 
         @Override
         protected void onPostExecute(Bitmap result) {
-            synchronized(mLoadedPreviews) {
-                mLoadedPreviews.put(mKey, new WeakReference<Bitmap>(result));
-            }
-
+            mBitmap = result;
             mCaller.applyPreview(result);
         }
     }