Fix 5607938 AudioFocusDeathHandler leaks GREF

The AudioFocus death handler was correctly updating the audio
 focus stack when an audio focus client dies, but the death handler
 was leaking GREF if unlinkToDeath() is not called.
The fix consists in making sure unlinkToDeath() is always called
 by calling it in its finalizer.

Change-Id: I0c5343b4986ab582cadbf171fc53816952dc16f5

Author: jmtrivi

media/java/android/media/AudioService.java

@@ -2693,11 +2693,22 @@ public FocusStackEntry(int streamType, int duration,
             mCallingUid = uid;
         }
 
-        public void unlinkToDeath() {
+        private void unlinkToDeath() {
             if (mSourceRef != null && mHandler != null) {
                 mSourceRef.unlinkToDeath(mHandler, 0);
             }
         }
+
+        @Override
+        protected void finalize() throws Throwable {
+            try {
+                unlinkToDeath();
+            } catch (java.util.NoSuchElementException e) {
+                Log.w(TAG, e + " thrown by unlinkToDeath() during finalize, ignoring");
+            } finally {
+                super.finalize();
+            }
+        }
     }
 
     private Stack<FocusStackEntry> mFocusStack = new Stack<FocusStackEntry>();
@@ -2732,8 +2743,7 @@ private void removeFocusStackEntry(String clientToRemove, boolean signal) {
         if (!mFocusStack.empty() && mFocusStack.peek().mClientId.equals(clientToRemove))
         {
             //Log.i(TAG, "   removeFocusStackEntry() removing top of stack");
-            FocusStackEntry fse = mFocusStack.pop();
-            fse.unlinkToDeath();
+            mFocusStack.pop();
             if (signal) {
                 // notify the new top of the stack it gained focus
                 notifyTopOfAudioFocusStack();
@@ -2752,7 +2762,6 @@ private void removeFocusStackEntry(String clientToRemove, boolean signal) {
                     Log.i(TAG, " AudioFocus  abandonAudioFocus(): removing entry for "
                             + fse.mClientId);
                     stackIterator.remove();
-                    fse.unlinkToDeath();
                 }
             }
         }
@@ -2858,6 +2867,9 @@ public int requestAudioFocus(int mainStreamType, int focusChangeHint, IBinder cb
                 // if focus is already owned by this client and the reason for acquiring the focus
                 // hasn't changed, don't do anything
                 if (mFocusStack.peek().mFocusChangeType == focusChangeHint) {
+                    // unlink death handler so it can be gc'ed.
+                    // linkToDeath() creates a JNI global reference preventing collection.
+                    cb.unlinkToDeath(afdh, 0);
                     return AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
                 }
                 // the reason for the audio focus request has changed: remove the current top of