Remove activity and window stacks when last task is removed.

Also,
* Only restore recent task to a full screen stack instead of any
  randomly sized stack.
* Fixed issue where we were restore task from recents for some
  operations when we didn't need to.
* Null out TaskRecord.stack when the task is removed from the
  stack.

Bug: 19083170
Change-Id: I4e006f101f9d0f2aebde130ad77afc4d258c6612

3 files changed, 26 insertions, 13 deletions

diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index 511347e..fe76073 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -7770,7 +7770,7 @@ public final class ActivityManagerService extends ActivityManagerNative
         synchronized (this) {
             enforceCallingPermission(android.Manifest.permission.READ_FRAME_BUFFER,
                     "getTaskThumbnail()");
-            TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(id);
+            TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(id, false);
             if (tr != null) {
                 return tr.getTaskThumbnailLocked();
             }
@@ -7883,7 +7883,7 @@ public final class ActivityManagerService extends ActivityManagerNative
     @Override
     public void setTaskResizeable(int taskId, boolean resizeable) {
         synchronized (this) {
-            TaskRecord task = mStackSupervisor.anyTaskForIdLocked(taskId);
+            TaskRecord task = mStackSupervisor.anyTaskForIdLocked(taskId, false);
             if (task == null) {
                 Slog.w(TAG, "setTaskResizeable: taskId=" + taskId + " not found");
                 return;
@@ -8031,7 +8031,7 @@ public final class ActivityManagerService extends ActivityManagerNative
      * @return Returns true if the given task was found and removed.
      */
     private boolean removeTaskByIdLocked(int taskId, boolean killProcess) {
-        TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(taskId);
+        TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(taskId, false);
         if (tr != null) {
             tr.removeTaskActivitiesLocked();
             cleanUpRemovedTaskLocked(tr, killProcess);
@@ -8285,7 +8285,7 @@ public final class ActivityManagerService extends ActivityManagerNative
         long ident = Binder.clearCallingIdentity();
         try {
             synchronized (this) {
-                TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(taskId);
+                TaskRecord tr = mStackSupervisor.anyTaskForIdLocked(taskId, false);
                 return tr != null && tr.stack != null && tr.stack.isHomeStack();
             }
         } finally {
diff --git a/services/core/java/com/android/server/am/ActivityStack.java b/services/core/java/com/android/server/am/ActivityStack.java
index 4d7305d..7afe23a 100644
--- a/services/core/java/com/android/server/am/ActivityStack.java
+++ b/services/core/java/com/android/server/am/ActivityStack.java
@@ -4171,6 +4171,8 @@ final class ActivityStack {
             }
             mActivityContainer.onTaskListEmptyLocked();
         }
+
+        task.stack = null;
     }
 
     TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent,
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index 1aa2a10..9fe3c48 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -462,6 +462,16 @@ public final class ActivityStackSupervisor implements DisplayListener {
     }
 
     TaskRecord anyTaskForIdLocked(int id) {
+        return anyTaskForIdLocked(id, true);
+    }
+
+    /**
+     * Returns a {@link TaskRecord} for the input id if available. Null otherwise.
+     * @param id Id of the task we would like returned.
+     * @param restoreFromRecents If the id was not in the active list, but was found in recents,
+     *                           restore the task from recents to the active list.
+     */
+    TaskRecord anyTaskForIdLocked(int id, boolean restoreFromRecents) {
         int numDisplays = mActivityDisplays.size();
         for (int displayNdx = 0; displayNdx < numDisplays; ++displayNdx) {
             ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
@@ -482,6 +492,10 @@ public final class ActivityStackSupervisor implements DisplayListener {
             return null;
         }
 
+        if (!restoreFromRecents) {
+            return task;
+        }
+
         if (!restoreRecentTaskLocked(task)) {
             if (DEBUG_RECENTS) Slog.w(TAG, "Couldn't restore task id=" + id + " found in recents");
             return null;
@@ -516,7 +530,7 @@ public final class ActivityStackSupervisor implements DisplayListener {
             if (mCurTaskId <= 0) {
                 mCurTaskId = 1;
             }
-        } while (anyTaskForIdLocked(mCurTaskId) != null);
+        } while (anyTaskForIdLocked(mCurTaskId, false) != null);
         return mCurTaskId;
     }
 
@@ -2661,7 +2675,7 @@ public final class ActivityStackSupervisor implements DisplayListener {
             final ArrayList<ActivityStack> homeDisplayStacks = mHomeStack.mStacks;
             for (int stackNdx = homeDisplayStacks.size() - 1; stackNdx >= 0; --stackNdx) {
                 final ActivityStack tmpStack = homeDisplayStacks.get(stackNdx);
-                if (!tmpStack.isHomeStack()) {
+                if (!tmpStack.isHomeStack() && tmpStack.mFullscreen) {
                     stack = tmpStack;
                     break;
                 }
@@ -3928,6 +3942,10 @@ public final class ActivityStackSupervisor implements DisplayListener {
         }
 
         void onTaskListEmptyLocked() {
+            mHandler.removeMessages(CONTAINER_TASK_LIST_EMPTY_TIMEOUT, this);
+            detachLocked();
+            deleteActivityContainer(this);
+            mHandler.obtainMessage(CONTAINER_CALLBACK_TASK_LIST_EMPTY, this).sendToTarget();
         }
 
         @Override
@@ -4016,13 +4034,6 @@ public final class ActivityStackSupervisor implements DisplayListener {
             return false;
         }
 
-        void onTaskListEmptyLocked() {
-            mHandler.removeMessages(CONTAINER_TASK_LIST_EMPTY_TIMEOUT, this);
-            detachLocked();
-            deleteActivityContainer(this);
-            mHandler.obtainMessage(CONTAINER_CALLBACK_TASK_LIST_EMPTY, this).sendToTarget();
-        }
-
         private void setSurfaceIfReadyLocked() {
             if (DEBUG_STACK) Slog.v(TAG, "setSurfaceIfReadyLocked: mDrawn=" + mDrawn +
                     " mContainerState=" + mContainerState + " mSurface=" + mSurface);