Pause animators when app is not visible

Because animators are not tied to the lifecycle of any UI
elements, it is possible for an app to go into the background
and for the animators to continue running. Ideally, the app would
track the lifecycle of the activity/etc and pause or disable the
animators, but it is common for this to not happen, causing the
animators to continue spinning when the app does not need them.
The animators are not causing as much work as for a foreground
activity (since they do not cause any re-rendering), but they cause
work nonetheless by keeping Choreographer awake to continue pulsing
frames.

The ideal fix would be to introduce new API for animators that
tied them to lifecycle concepts (View, Activity, etc). But that kind
of fix would only be available for future versions of the platform,
and does not address existing app code. A workaround for the current
situation is to address the most egregious problems; infinite animators
running on backgrounded apps.

The fix here is exactly that: when an app's visible surface (either an
activity or, for Wallpapers, a WallpaperService) is backgrounded,
a request is sent to pause animators for that surface. When that surface
comes to the foreground, a request is sent to resume those animators.
Since all animators are handled on the same thread for the same process,
in AnimationHandler, we should only ever pause animators when *all*
surfaces for a process are not visible (and resume them when *any*
surface becomes visible). Also, to mitigate any issues with thrashing
animator state for apps which become only transiently backgrounded,
we delay pausing for some time.

Bug: 228598053
Bug: 233391022
Test: new AnimatorLeak CTS test, plus manual testing for activities
    and wallpapers

Change-Id: I8b9f841cc80babb972244c724968a5c085a06b69
Merged-In: I8b9f841cc80babb972244c724968a5c085a06b69

1 files changed, 109 insertions, 1 deletions

diff --git a/core/java/android/animation/AnimationHandler.java b/core/java/android/animation/AnimationHandler.java
index 260323fe2d10..7f6df2261fcc 100644
--- a/core/java/android/animation/AnimationHandler.java
+++ b/core/java/android/animation/AnimationHandler.java
@@ -18,6 +18,8 @@ package android.animation;
 
 import android.os.SystemClock;
 import android.util.ArrayMap;
+import android.util.ArraySet;
+import android.util.Log;
 import android.view.Choreographer;
 
 import java.util.ArrayList;
@@ -35,10 +37,13 @@ import java.util.ArrayList;
  * @hide
  */
 public class AnimationHandler {
+
+    private static final String TAG = "AnimationHandler";
+    private static final boolean LOCAL_LOGV = true;
+
     /**
      * Internal per-thread collections used to avoid set collisions as animations start and end
      * while being processed.
-     * @hide
      */
     private final ArrayMap<AnimationFrameCallback, Long> mDelayedCallbackStartTime =
             new ArrayMap<>();
@@ -48,6 +53,26 @@ public class AnimationHandler {
             new ArrayList<>();
     private AnimationFrameCallbackProvider mProvider;
 
+    /**
+     * This paused list is used to store animators forcibly paused when the activity
+     * went into the background (to avoid unnecessary background processing work).
+     * These animators should be resume()'d when the activity returns to the foreground.
+     */
+    private final ArrayList<Animator> mPausedAnimators = new ArrayList<>();
+
+    /**
+     * This structure is used to store the currently active objects (ViewRootImpls or
+     * WallpaperService.Engines) in the process. Each of these objects sends a request to
+     * AnimationHandler when it goes into the background (request to pause) or foreground
+     * (request to resume). Because all animators are managed by AnimationHandler on the same
+     * thread, it should only ever pause animators when *all* requestors are in the background.
+     * This list tracks the background/foreground state of all requestors and only ever
+     * pauses animators when all items are in the background (false). To simplify, we only ever
+     * store visible (foreground) requestors; if the set size reaches zero, there are no
+     * objects in the foreground and it is time to pause animators.
+     */
+    private final ArraySet<Object> mAnimatorRequestors = new ArraySet<>();
+
     private final Choreographer.FrameCallback mFrameCallback = new Choreographer.FrameCallback() {
         @Override
         public void doFrame(long frameTimeNanos) {
@@ -68,6 +93,89 @@ public class AnimationHandler {
         return sAnimatorHandler.get();
     }
 
+
+    /**
+     * This is called when a window goes away. We should remove
+     * it from the requestors list to ensure that we are counting requests correctly and not
+     * tracking obsolete+enabled requestors.
+     */
+    public static void removeRequestor(Object requestor) {
+        getInstance().removeRequestorImpl(requestor);
+    }
+
+    private void removeRequestorImpl(Object requestor) {
+        // Also request disablement, in case that requestor was the sole object keeping
+        // animators un-paused
+        requestAnimatorsEnabled(false, requestor);
+        mAnimatorRequestors.remove(requestor);
+        if (LOCAL_LOGV) {
+            Log.v(TAG, "removeRequestorImpl for " + requestor);
+            for (int i = 0; i < mAnimatorRequestors.size(); ++i) {
+                Log.v(TAG, "animatorRequesters " + i + " = " + mAnimatorRequestors.valueAt(i));
+            }
+        }
+    }
+
+    /**
+     * This method is called from ViewRootImpl or WallpaperService when either a window is no
+     * longer visible (enable == false) or when a window becomes visible (enable == true).
+     * If animators are not properly disabled when activities are backgrounded, it can lead to
+     * unnecessary processing, particularly for infinite animators, as the system will continue
+     * to pulse timing events even though the results are not visible. As a workaround, we
+     * pause all un-paused infinite animators, and resume them when any window in the process
+     * becomes visible.
+     */
+    public static void requestAnimatorsEnabled(boolean enable, Object requestor) {
+        getInstance().requestAnimatorsEnabledImpl(enable, requestor);
+    }
+
+    private void requestAnimatorsEnabledImpl(boolean enable, Object requestor) {
+        boolean wasEmpty = mAnimatorRequestors.isEmpty();
+        if (enable) {
+            mAnimatorRequestors.add(requestor);
+        } else {
+            mAnimatorRequestors.remove(requestor);
+        }
+        boolean isEmpty = mAnimatorRequestors.isEmpty();
+        if (wasEmpty != isEmpty) {
+            // only paused/resume animators if there was a visibility change
+            if (!isEmpty) {
+                // If any requestors are enabled, resume currently paused animators
+                Choreographer.getInstance().removeFrameCallback(mPauser);
+                for (int i = mPausedAnimators.size() - 1; i >= 0; --i) {
+                    mPausedAnimators.get(i).resume();
+                }
+                mPausedAnimators.clear();
+            } else {
+                // Wait before pausing to avoid thrashing animator state for temporary backgrounding
+                Choreographer.getInstance().postFrameCallbackDelayed(mPauser,
+                        Animator.getBackgroundPauseDelay());
+            }
+        }
+        if (LOCAL_LOGV) {
+            Log.v(TAG, enable ? "enable" : "disable" + " animators for " + requestor);
+            for (int i = 0; i < mAnimatorRequestors.size(); ++i) {
+                Log.v(TAG, "animatorRequesters " + i + " = " + mAnimatorRequestors.valueAt(i));
+            }
+        }
+    }
+
+    private Choreographer.FrameCallback mPauser = frameTimeNanos -> {
+        if (mAnimatorRequestors.size() > 0) {
+            // something enabled animators since this callback was scheduled - bail
+            return;
+        }
+        for (int i = 0; i < mAnimationCallbacks.size(); ++i) {
+            Animator animator = ((Animator) mAnimationCallbacks.get(i));
+            if (animator != null
+                    && animator.getTotalDuration() == Animator.DURATION_INFINITE
+                    && !animator.isPaused()) {
+                mPausedAnimators.add(animator);
+                animator.pause();
+            }
+        }
+    };
+
     /**
      * By default, the Choreographer is used to provide timing for frame callbacks. A custom
      * provider can be used here to provide different timing pulse.