Insert home task into history when sending to back.

- There is an assumption that moving a task to the back moves it
behind the home activity. This fix ensures that the home activity
will be launched by some activity before the task that has been
moved to the back.

- Convert "private final" declarations to private only.

- Convert container tests for size()==0 to isEmpty().

- Remove unused variable.

Fixes bug 10228536.

Change-Id: I51741ee7a09652e27afffcc50c14953bf0aa27ea

2 files changed, 45 insertions, 16 deletions

diff --git a/services/java/com/android/server/am/ActivityManagerService.java b/services/java/com/android/server/am/ActivityManagerService.java
index 4678b8517ce8..181359312e01 100644
--- a/services/java/com/android/server/am/ActivityManagerService.java
+++ b/services/java/com/android/server/am/ActivityManagerService.java
@@ -6517,8 +6517,11 @@ public final class ActivityManagerService extends ActivityManagerNative
                     }
                 }
                 final long origId = Binder.clearCallingIdentity();
-                stack.moveTaskToBackLocked(taskId, null);
-                Binder.restoreCallingIdentity(origId);
+                try {
+                    stack.moveTaskToBackLocked(taskId, null);
+                } finally {
+                    Binder.restoreCallingIdentity(origId);
+                }
             }
         }
     }
diff --git a/services/java/com/android/server/am/ActivityStack.java b/services/java/com/android/server/am/ActivityStack.java
index 2fefadf02b48..8d27c5cb39b4 100644
--- a/services/java/com/android/server/am/ActivityStack.java
+++ b/services/java/com/android/server/am/ActivityStack.java
@@ -255,7 +255,7 @@ final class ActivityStack {
         //public Handler() {
         //    if (localLOGV) Slog.v(TAG, "Handler started!");
         //}
-        public ActivityStackHandler(Looper looper) {
+        ActivityStackHandler(Looper looper) {
             super(looper);
         }
 
@@ -331,7 +331,6 @@ final class ActivityStack {
         mWindowManager = service.mWindowManager;
         mStackSupervisor = service.mStackSupervisor;
         mContext = context;
-        PowerManager pm = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
         mStackId = stackId;
         mCurrentUser = service.mCurrentUserId;
     }
@@ -837,7 +836,7 @@ final class ActivityStack {
         }
     }
 
-    private final void completePauseLocked() {
+    private void completePauseLocked() {
         ActivityRecord prev = mPausingActivity;
         if (DEBUG_PAUSE) Slog.v(TAG, "Complete pause: " + prev);
 
@@ -1765,7 +1764,7 @@ final class ActivityStack {
         for (int taskNdx = 0; taskNdx < numTasks; ++taskNdx) {
             TaskRecord task = mTaskHistory.get(taskNdx);
             final ArrayList<ActivityRecord> activities = task.mActivities;
-            if (activities.size() == 0) {
+            if (activities.isEmpty()) {
                 continue;
             }
             TaskGroup group = new TaskGroup();
@@ -2335,7 +2334,7 @@ final class ActivityStack {
 
         finishActivityResultsLocked(r, resultCode, resultData);
 
-        if (mService.mPendingThumbnails.size() > 0) {
+        if (!mService.mPendingThumbnails.isEmpty()) {
             // There are clients waiting to receive thumbnails so, in case
             // this is an activity that someone is waiting for, add it
             // to the pending list so we can correctly update the clients.
@@ -2561,7 +2560,7 @@ final class ActivityStack {
             cleanUpActivityServicesLocked(r);
         }
 
-        if (mService.mPendingThumbnails.size() > 0) {
+        if (!mService.mPendingThumbnails.isEmpty()) {
             // There are clients waiting to receive thumbnails so, in case
             // this is an activity that someone is waiting for, add it
             // to the pending list so we can correctly update the clients.
@@ -2698,7 +2697,7 @@ final class ActivityStack {
                     mService.mHandler.sendEmptyMessage(
                             ActivityManagerService.CANCEL_HEAVY_NOTIFICATION_MSG);
                 }
-                if (r.app.activities.size() == 0) {
+                if (r.app.activities.isEmpty()) {
                     // No longer have activities, so update oom adj.
                     mService.updateOomAdjLocked();
                 }
@@ -3009,9 +3008,38 @@ final class ActivityStack {
         if (tr == null) {
             return false;
         }
+
         mTaskHistory.remove(tr);
         mTaskHistory.add(0, tr);
 
+        // There is an assumption that moving a task to the back moves it behind the home activity.
+        // We make sure here that some activity in the stack will launch home.
+        ActivityRecord lastActivity = null;
+        int numTasks = mTaskHistory.size();
+        int taskNdx;
+        for (taskNdx = numTasks - 1; taskNdx >= 1; --taskNdx) {
+            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
+            int activityNdx;
+            for (activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
+                final ActivityRecord r = activities.get(activityNdx);
+                if (r.mLaunchHomeTaskNext) {
+                    break;
+                }
+                if (taskNdx == 1 && activityNdx == 0) {
+                    // Final activity before tr task.
+                    lastActivity = r;
+                }
+            }
+            if (activityNdx >= 0) {
+                // Early exit, we found an activity that will launchHomeTaskNext.
+                break;
+            }
+        }
+        if (lastActivity != null) {
+            // No early exit, we did not find an activity that will launchHomeTaskNext, set one.
+            lastActivity.mLaunchHomeTaskNext = true;
+        }
+
         if (reason != null &&
                 (reason.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0) {
             mWindowManager.prepareAppTransition(AppTransition.TRANSIT_NONE, false);
@@ -3020,8 +3048,7 @@ final class ActivityStack {
                 mNoAnimActivities.add(r);
             }
         } else {
-            mWindowManager.prepareAppTransition(
-                    AppTransition.TRANSIT_TASK_TO_BACK, false);
+            mWindowManager.prepareAppTransition(AppTransition.TRANSIT_TASK_TO_BACK, false);
         }
         mWindowManager.moveTaskToBottom(task);
 
@@ -3029,9 +3056,8 @@ final class ActivityStack {
             validateAppTokensLocked();
         }
 
-        if (mResumedActivity != null && mResumedActivity.task == tr &&
-                mResumedActivity.mLaunchHomeTaskNext) {
-            // TODO: Can we skip the next line and just pass mResumedAct. to resumeHomeAct.()?
+        if (numTasks <= 1 || (mResumedActivity != null && mResumedActivity.task == tr &&
+                mResumedActivity.mLaunchHomeTaskNext)) {
             mResumedActivity.mLaunchHomeTaskNext = false;
             return mStackSupervisor.resumeHomeActivity(null);
         }
@@ -3175,7 +3201,7 @@ final class ActivityStack {
         return true;
     }
 
-    private final boolean relaunchActivityLocked(ActivityRecord r,
+    private boolean relaunchActivityLocked(ActivityRecord r,
             int changes, boolean andResume) {
         List<ResultInfo> results = null;
         List<Intent> newIntents = null;
@@ -3487,7 +3513,7 @@ final class ActivityStack {
 
     boolean removeTask(TaskRecord task) {
         mTaskHistory.remove(task);
-        return mTaskHistory.size() == 0;
+        return mTaskHistory.isEmpty();
     }
 
     TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent, boolean toTop) {