xref: /frameworks/base/services/core/java/com/android/server/am/ActivityStack.java

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.server.am;

import static android.app.ActivityManager.StackId.DOCKED_STACK_ID;
import static android.app.ActivityManager.StackId.FREEFORM_WORKSPACE_STACK_ID;
import static android.app.ActivityManager.StackId.FULLSCREEN_WORKSPACE_STACK_ID;
import static android.app.ActivityManager.StackId.HOME_STACK_ID;
import static android.app.ActivityManager.StackId.INVALID_STACK_ID;
import static android.app.ActivityManager.StackId.PINNED_STACK_ID;
import static android.content.pm.ActivityInfo.CONFIG_ORIENTATION;
import static android.content.pm.ActivityInfo.CONFIG_SCREEN_LAYOUT;
import static android.content.pm.ActivityInfo.CONFIG_SCREEN_SIZE;
import static android.content.pm.ActivityInfo.CONFIG_SMALLEST_SCREEN_SIZE;
import static android.content.pm.ActivityInfo.FLAG_RESUME_WHILE_PAUSING;
import static android.content.pm.ActivityInfo.FLAG_SHOW_FOR_ALL_USERS;
import static android.content.res.Configuration.SCREENLAYOUT_UNDEFINED;
import static android.view.Display.DEFAULT_DISPLAY;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_ADD_REMOVE;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_ALL;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_APP;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_CLEANUP;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_CONFIGURATION;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_CONTAINERS;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_LOCKSCREEN;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_PAUSE;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_RELEASE;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_RESULTS;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_SAVED_STATE;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_SCREENSHOTS;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_STACK;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_STATES;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_SWITCH;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_TASKS;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_TRANSITION;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_USER_LEAVING;
import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_VISIBILITY;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_ADD_REMOVE;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_APP;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_CLEANUP;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_CONFIGURATION;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_CONTAINERS;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_PAUSE;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_RELEASE;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_RESULTS;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_SAVED_STATE;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_SCREENSHOTS;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_STACK;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_STATES;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_SWITCH;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_TASKS;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_TRANSITION;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_USER_LEAVING;
import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_VISIBILITY;
import static com.android.server.am.ActivityManagerDebugConfig.TAG_AM;
import static com.android.server.am.ActivityManagerDebugConfig.TAG_WITH_CLASS_NAME;
import static com.android.server.am.ActivityManagerService.LOCK_SCREEN_SHOWN;
import static com.android.server.am.ActivityManagerService.TAKE_FULLSCREEN_SCREENSHOTS;
import static com.android.server.am.ActivityRecord.APPLICATION_ACTIVITY_TYPE;
import static com.android.server.am.ActivityRecord.HOME_ACTIVITY_TYPE;
import static com.android.server.am.ActivityRecord.STARTING_WINDOW_REMOVED;
import static com.android.server.am.ActivityRecord.STARTING_WINDOW_SHOWN;
import static com.android.server.am.ActivityStackSupervisor.FindTaskResult;
import static com.android.server.am.ActivityStackSupervisor.ON_TOP;
import static com.android.server.am.ActivityStackSupervisor.PRESERVE_WINDOWS;
import static com.android.server.wm.AppTransition.TRANSIT_ACTIVITY_CLOSE;
import static com.android.server.wm.AppTransition.TRANSIT_ACTIVITY_OPEN;
import static com.android.server.wm.AppTransition.TRANSIT_NONE;
import static com.android.server.wm.AppTransition.TRANSIT_TASK_CLOSE;
import static com.android.server.wm.AppTransition.TRANSIT_TASK_OPEN;
import static com.android.server.wm.AppTransition.TRANSIT_TASK_OPEN_BEHIND;
import static com.android.server.wm.AppTransition.TRANSIT_TASK_TO_BACK;
import static com.android.server.wm.AppTransition.TRANSIT_TASK_TO_FRONT;

import android.app.Activity;
import android.app.ActivityManager;
import android.app.ActivityManager.RunningTaskInfo;
import android.app.ActivityManager.StackId;
import android.app.ActivityOptions;
import android.app.AppGlobals;
import android.app.IActivityController;
import android.app.ResultInfo;
import android.content.ComponentName;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.content.pm.ApplicationInfo;
import android.content.res.Configuration;
import android.graphics.Bitmap;
import android.graphics.Point;
import android.graphics.Rect;
import android.net.Uri;
import android.os.Binder;
import android.os.Bundle;
import android.os.Debug;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.PersistableBundle;
import android.os.RemoteException;
import android.os.SystemClock;
import android.os.Trace;
import android.os.UserHandle;
import android.service.voice.IVoiceInteractionSession;
import android.util.ArraySet;
import android.util.EventLog;
import android.util.Log;
import android.util.Slog;
import android.view.Display;

import com.android.internal.app.IVoiceInteractor;
import com.android.internal.content.ReferrerIntent;
import com.android.internal.os.BatteryStatsImpl;
import com.android.server.Watchdog;
import com.android.server.am.ActivityManagerService.ItemMatcher;
import com.android.server.am.ActivityStackSupervisor.ActivityContainer;
import com.android.server.wm.TaskGroup;
import com.android.server.wm.WindowManagerService;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.Set;

/**
 * State and management of a single stack of activities.
 */
final class ActivityStack {

    private static final String TAG = TAG_WITH_CLASS_NAME ? "ActivityStack" : TAG_AM;
    private static final String TAG_ADD_REMOVE = TAG + POSTFIX_ADD_REMOVE;
    private static final String TAG_APP = TAG + POSTFIX_APP;
    private static final String TAG_CLEANUP = TAG + POSTFIX_CLEANUP;
    private static final String TAG_CONFIGURATION = TAG + POSTFIX_CONFIGURATION;
    private static final String TAG_CONTAINERS = TAG + POSTFIX_CONTAINERS;
    private static final String TAG_PAUSE = TAG + POSTFIX_PAUSE;
    private static final String TAG_RELEASE = TAG + POSTFIX_RELEASE;
    private static final String TAG_RESULTS = TAG + POSTFIX_RESULTS;
    private static final String TAG_SAVED_STATE = TAG + POSTFIX_SAVED_STATE;
    private static final String TAG_SCREENSHOTS = TAG + POSTFIX_SCREENSHOTS;
    private static final String TAG_STACK = TAG + POSTFIX_STACK;
    private static final String TAG_STATES = TAG + POSTFIX_STATES;
    private static final String TAG_SWITCH = TAG + POSTFIX_SWITCH;
    private static final String TAG_TASKS = TAG + POSTFIX_TASKS;
    private static final String TAG_TRANSITION = TAG + POSTFIX_TRANSITION;
    private static final String TAG_USER_LEAVING = TAG + POSTFIX_USER_LEAVING;
    private static final String TAG_VISIBILITY = TAG + POSTFIX_VISIBILITY;

    private static final boolean VALIDATE_TOKENS = false;

    // Ticks during which we check progress while waiting for an app to launch.
    static final int LAUNCH_TICK = 500;

    // How long we wait until giving up on the last activity to pause.  This
    // is short because it directly impacts the responsiveness of starting the
    // next activity.
    static final int PAUSE_TIMEOUT = 500;

    // How long we wait for the activity to tell us it has stopped before
    // giving up.  This is a good amount of time because we really need this
    // from the application in order to get its saved state.
    static final int STOP_TIMEOUT = 10 * 1000;

    // How long we wait until giving up on an activity telling us it has
    // finished destroying itself.
    static final int DESTROY_TIMEOUT = 10 * 1000;

    // How long until we reset a task when the user returns to it.  Currently
    // disabled.
    static final long ACTIVITY_INACTIVE_RESET_TIME = 0;

    // How long between activity launches that we consider safe to not warn
    // the user about an unexpected activity being launched on top.
    static final long START_WARN_TIME = 5 * 1000;

    // Set to false to disable the preview that is shown while a new activity
    // is being started.
    static final boolean SHOW_APP_STARTING_PREVIEW = true;

    // How long to wait for all background Activities to redraw following a call to
    // convertToTranslucent().
    static final long TRANSLUCENT_CONVERSION_TIMEOUT = 2000;

    // How many activities have to be scheduled to stop to force a stop pass.
    private static final int MAX_STOPPING_TO_FORCE = 3;

    enum ActivityState {
        INITIALIZING,
        RESUMED,
        PAUSING,
        PAUSED,
        STOPPING,
        STOPPED,
        FINISHING,
        DESTROYING,
        DESTROYED
    }

    // Stack is not considered visible.
    static final int STACK_INVISIBLE = 0;
    // Stack is considered visible
    static final int STACK_VISIBLE = 1;
    // Stack is considered visible, but only becuase it has activity that is visible behind other
    // activities and there is a specific combination of stacks.
    static final int STACK_VISIBLE_ACTIVITY_BEHIND = 2;

    /* The various modes for the method {@link #removeTask}. */
    // Task is being completely removed from all stacks in the system.
    static final int REMOVE_TASK_MODE_DESTROYING = 0;
    // Task is being removed from this stack so we can add it to another stack. In the case we are
    // moving we don't want to perform some operations on the task like removing it from window
    // manager or recents.
    static final int REMOVE_TASK_MODE_MOVING = 1;
    // Similar to {@link #REMOVE_TASK_MODE_MOVING} and the task will be added to the top of its new
    // stack and the new stack will be on top of all stacks.
    static final int REMOVE_TASK_MODE_MOVING_TO_TOP = 2;

    final ActivityManagerService mService;
    final WindowManagerService mWindowManager;
    private final RecentTasks mRecentTasks;

    /**
     * The back history of all previous (and possibly still
     * running) activities.  It contains #TaskRecord objects.
     */
    private final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>();

    /**
     * Used for validating app tokens with window manager.
     */
    final ArrayList<TaskGroup> mValidateAppTokens = new ArrayList<>();

    /**
     * List of running activities, sorted by recent usage.
     * The first entry in the list is the least recently used.
     * It contains HistoryRecord objects.
     */
    final ArrayList<ActivityRecord> mLRUActivities = new ArrayList<>();

    /**
     * Animations that for the current transition have requested not to
     * be considered for the transition animation.
     */
    final ArrayList<ActivityRecord> mNoAnimActivities = new ArrayList<>();

    /**
     * When we are in the process of pausing an activity, before starting the
     * next one, this variable holds the activity that is currently being paused.
     */
    ActivityRecord mPausingActivity = null;

    /**
     * This is the last activity that we put into the paused state.  This is
     * used to determine if we need to do an activity transition while sleeping,
     * when we normally hold the top activity paused.
     */
    ActivityRecord mLastPausedActivity = null;

    /**
     * Activities that specify No History must be removed once the user navigates away from them.
     * If the device goes to sleep with such an activity in the paused state then we save it here
     * and finish it later if another activity replaces it on wakeup.
     */
    ActivityRecord mLastNoHistoryActivity = null;

    /**
     * Current activity that is resumed, or null if there is none.
     */
    ActivityRecord mResumedActivity = null;

    /**
     * This is the last activity that has been started.  It is only used to
     * identify when multiple activities are started at once so that the user
     * can be warned they may not be in the activity they think they are.
     */
    ActivityRecord mLastStartedActivity = null;

    // The topmost Activity passed to convertToTranslucent(). When non-null it means we are
    // waiting for all Activities in mUndrawnActivitiesBelowTopTranslucent to be removed as they
    // are drawn. When the last member of mUndrawnActivitiesBelowTopTranslucent is removed the
    // Activity in mTranslucentActivityWaiting is notified via
    // Activity.onTranslucentConversionComplete(false). If a timeout occurs prior to the last
    // background activity being drawn then the same call will be made with a true value.
    ActivityRecord mTranslucentActivityWaiting = null;
    private ArrayList<ActivityRecord> mUndrawnActivitiesBelowTopTranslucent = new ArrayList<>();

    /**
     * Set when we know we are going to be calling updateConfiguration()
     * soon, so want to skip intermediate config checks.
     */
    boolean mConfigWillChange;

    // Whether or not this stack covers the entire screen; by default stacks are fullscreen
    boolean mFullscreen = true;
    // Current bounds of the stack or null if fullscreen.
    Rect mBounds = null;

    boolean mUpdateBoundsDeferred;
    boolean mUpdateBoundsDeferredCalled;
    final Rect mDeferredBounds = new Rect();
    final Rect mDeferredTaskBounds = new Rect();
    final Rect mDeferredTaskInsetBounds = new Rect();

    long mLaunchStartTime = 0;
    long mFullyDrawnStartTime = 0;

    int mCurrentUser;

    final int mStackId;
    final ActivityContainer mActivityContainer;
    /** The other stacks, in order, on the attached display. Updated at attach/detach time. */
    ArrayList<ActivityStack> mStacks;
    /** The attached Display's unique identifier, or -1 if detached */
    int mDisplayId;

    /** Run all ActivityStacks through this */
    final ActivityStackSupervisor mStackSupervisor;

    private final LaunchingTaskPositioner mTaskPositioner;

    static final int PAUSE_TIMEOUT_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 1;
    static final int DESTROY_TIMEOUT_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 2;
    static final int LAUNCH_TICK_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 3;
    static final int STOP_TIMEOUT_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 4;
    static final int DESTROY_ACTIVITIES_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 5;
    static final int TRANSLUCENT_TIMEOUT_MSG = ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 6;
    static final int RELEASE_BACKGROUND_RESOURCES_TIMEOUT_MSG =
            ActivityManagerService.FIRST_ACTIVITY_STACK_MSG + 7;

    static class ScheduleDestroyArgs {
        final ProcessRecord mOwner;
        final String mReason;
        ScheduleDestroyArgs(ProcessRecord owner, String reason) {
            mOwner = owner;
            mReason = reason;
        }
    }

    final Handler mHandler;

    final class ActivityStackHandler extends Handler {

        ActivityStackHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case PAUSE_TIMEOUT_MSG: {
                    ActivityRecord r = (ActivityRecord)msg.obj;
                    // We don't at this point know if the activity is fullscreen,
                    // so we need to be conservative and assume it isn't.
                    Slog.w(TAG, "Activity pause timeout for " + r);
                    synchronized (mService) {
                        if (r.app != null) {
                            mService.logAppTooSlow(r.app, r.pauseTime, "pausing " + r);
                        }
                        activityPausedLocked(r.appToken, true);
                    }
                } break;
                case LAUNCH_TICK_MSG: {
                    ActivityRecord r = (ActivityRecord)msg.obj;
                    synchronized (mService) {
                        if (r.continueLaunchTickingLocked()) {
                            mService.logAppTooSlow(r.app, r.launchTickTime, "launching " + r);
                        }
                    }
                } break;
                case DESTROY_TIMEOUT_MSG: {
                    ActivityRecord r = (ActivityRecord)msg.obj;
                    // We don't at this point know if the activity is fullscreen,
                    // so we need to be conservative and assume it isn't.
                    Slog.w(TAG, "Activity destroy timeout for " + r);
                    synchronized (mService) {
                        activityDestroyedLocked(r != null ? r.appToken : null, "destroyTimeout");
                    }
                } break;
                case STOP_TIMEOUT_MSG: {
                    ActivityRecord r = (ActivityRecord)msg.obj;
                    // We don't at this point know if the activity is fullscreen,
                    // so we need to be conservative and assume it isn't.
                    Slog.w(TAG, "Activity stop timeout for " + r);
                    synchronized (mService) {
                        if (r.isInHistory()) {
                            activityStoppedLocked(r, null, null, null);
                        }
                    }
                } break;
                case DESTROY_ACTIVITIES_MSG: {
                    ScheduleDestroyArgs args = (ScheduleDestroyArgs)msg.obj;
                    synchronized (mService) {
                        destroyActivitiesLocked(args.mOwner, args.mReason);
                    }
                } break;
                case TRANSLUCENT_TIMEOUT_MSG: {
                    synchronized (mService) {
                        notifyActivityDrawnLocked(null);
                    }
                } break;
                case RELEASE_BACKGROUND_RESOURCES_TIMEOUT_MSG: {
                    synchronized (mService) {
                        final ActivityRecord r = getVisibleBehindActivity();
                        Slog.e(TAG, "Timeout waiting for cancelVisibleBehind player=" + r);
                        if (r != null) {
                            mService.killAppAtUsersRequest(r.app, null);
                        }
                    }
                } break;
            }
        }
    }

    int numActivities() {
        int count = 0;
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            count += mTaskHistory.get(taskNdx).mActivities.size();
        }
        return count;
    }

    ActivityStack(ActivityStackSupervisor.ActivityContainer activityContainer,
            RecentTasks recentTasks) {
        mActivityContainer = activityContainer;
        mStackSupervisor = activityContainer.getOuter();
        mService = mStackSupervisor.mService;
        mHandler = new ActivityStackHandler(mService.mHandler.getLooper());
        mWindowManager = mService.mWindowManager;
        mStackId = activityContainer.mStackId;
        mCurrentUser = mService.mUserController.getCurrentUserIdLocked();
        mRecentTasks = recentTasks;
        mTaskPositioner = mStackId == FREEFORM_WORKSPACE_STACK_ID
                ? new LaunchingTaskPositioner() : null;
    }

    void attachDisplay(ActivityStackSupervisor.ActivityDisplay activityDisplay, boolean onTop) {
        mDisplayId = activityDisplay.mDisplayId;
        mStacks = activityDisplay.mStacks;
        mBounds = mWindowManager.attachStack(mStackId, activityDisplay.mDisplayId, onTop);
        mFullscreen = mBounds == null;
        if (mTaskPositioner != null) {
            mTaskPositioner.setDisplay(activityDisplay.mDisplay);
            mTaskPositioner.configure(mBounds);
        }

        if (mStackId == DOCKED_STACK_ID) {
            // If we created a docked stack we want to resize it so it resizes all other stacks
            // in the system.
            mStackSupervisor.resizeDockedStackLocked(
                    mBounds, null, null, null, null, PRESERVE_WINDOWS);
        }
    }

    void detachDisplay() {
        mDisplayId = Display.INVALID_DISPLAY;
        mStacks = null;
        if (mTaskPositioner != null) {
            mTaskPositioner.reset();
        }
        mWindowManager.detachStack(mStackId);
        if (mStackId == DOCKED_STACK_ID) {
            // If we removed a docked stack we want to resize it so it resizes all other stacks
            // in the system to fullscreen.
            mStackSupervisor.resizeDockedStackLocked(
                    null, null, null, null, null, PRESERVE_WINDOWS);
        }
    }

    public void getDisplaySize(Point out) {
        mActivityContainer.mActivityDisplay.mDisplay.getSize(out);
    }

    /**
     * Defers updating the bounds of the stack. If the stack was resized/repositioned while
     * deferring, the bounds will update in {@link #continueUpdateBounds()}.
     */
    void deferUpdateBounds() {
        if (!mUpdateBoundsDeferred) {
            mUpdateBoundsDeferred = true;
            mUpdateBoundsDeferredCalled = false;
        }
    }

    /**
     * Continues updating bounds after updates have been deferred. If there was a resize attempt
     * between {@link #deferUpdateBounds()} and {@link #continueUpdateBounds()}, the stack will
     * be resized to that bounds.
     */
    void continueUpdateBounds() {
        final boolean wasDeferred = mUpdateBoundsDeferred;
        mUpdateBoundsDeferred = false;
        if (wasDeferred && mUpdateBoundsDeferredCalled) {
            mStackSupervisor.resizeStackUncheckedLocked(this,
                    mDeferredBounds.isEmpty() ? null : mDeferredBounds,
                    mDeferredTaskBounds.isEmpty() ? null : mDeferredTaskBounds,
                    mDeferredTaskInsetBounds.isEmpty() ? null : mDeferredTaskInsetBounds);
        }
    }

    boolean updateBoundsAllowed(Rect bounds, Rect tempTaskBounds,
            Rect tempTaskInsetBounds) {
        if (!mUpdateBoundsDeferred) {
            return true;
        }
        if (bounds != null) {
            mDeferredBounds.set(bounds);
        } else {
            mDeferredBounds.setEmpty();
        }
        if (tempTaskBounds != null) {
            mDeferredTaskBounds.set(tempTaskBounds);
        } else {
            mDeferredTaskBounds.setEmpty();
        }
        if (tempTaskInsetBounds != null) {
            mDeferredTaskInsetBounds.set(tempTaskInsetBounds);
        } else {
            mDeferredTaskInsetBounds.setEmpty();
        }
        mUpdateBoundsDeferredCalled = true;
        return false;
    }

    void setBounds(Rect bounds) {
        mBounds = mFullscreen ? null : new Rect(bounds);
        if (mTaskPositioner != null) {
            mTaskPositioner.configure(bounds);
        }
    }

    boolean okToShowLocked(ActivityRecord r) {
        return mStackSupervisor.okToShowLocked(r);
    }

    final ActivityRecord topRunningActivityLocked() {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            ActivityRecord r = mTaskHistory.get(taskNdx).topRunningActivityLocked();
            if (r != null) {
                return r;
            }
        }
        return null;
    }

    final ActivityRecord topRunningNonDelayedActivityLocked(ActivityRecord notTop) {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            final ArrayList<ActivityRecord> activities = task.mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                ActivityRecord r = activities.get(activityNdx);
                if (!r.finishing && !r.delayedResume && r != notTop && okToShowLocked(r)) {
                    return r;
                }
            }
        }
        return null;
    }

    /**
     * This is a simplified version of topRunningActivityLocked that provides a number of
     * optional skip-over modes.  It is intended for use with the ActivityController hook only.
     *
     * @param token If non-null, any history records matching this token will be skipped.
     * @param taskId If non-zero, we'll attempt to skip over records with the same task ID.
     *
     * @return Returns the HistoryRecord of the next activity on the stack.
     */
    final ActivityRecord topRunningActivityLocked(IBinder token, int taskId) {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            TaskRecord task = mTaskHistory.get(taskNdx);
            if (task.taskId == taskId) {
                continue;
            }
            ArrayList<ActivityRecord> activities = task.mActivities;
            for (int i = activities.size() - 1; i >= 0; --i) {
                final ActivityRecord r = activities.get(i);
                // Note: the taskId check depends on real taskId fields being non-zero
                if (!r.finishing && (token != r.appToken) && okToShowLocked(r)) {
                    return r;
                }
            }
        }
        return null;
    }

    final ActivityRecord topActivity() {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                if (!r.finishing) {
                    return r;
                }
            }
        }
        return null;
    }

    final TaskRecord topTask() {
        final int size = mTaskHistory.size();
        if (size > 0) {
            return mTaskHistory.get(size - 1);
        }
        return null;
    }

    TaskRecord taskForIdLocked(int id) {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            if (task.taskId == id) {
                return task;
            }
        }
        return null;
    }

    ActivityRecord isInStackLocked(IBinder token) {
        final ActivityRecord r = ActivityRecord.forTokenLocked(token);
        return isInStackLocked(r);
    }

    ActivityRecord isInStackLocked(ActivityRecord r) {
        if (r == null) {
            return null;
        }
        final TaskRecord task = r.task;
        if (task != null && task.stack != null
                && task.mActivities.contains(r) && mTaskHistory.contains(task)) {
            if (task.stack != this) Slog.w(TAG,
                    "Illegal state! task does not point to stack it is in.");
            return r;
        }
        return null;
    }

    final boolean updateLRUListLocked(ActivityRecord r) {
        final boolean hadit = mLRUActivities.remove(r);
        mLRUActivities.add(r);
        return hadit;
    }

    final boolean isHomeStack() {
        return mStackId == HOME_STACK_ID;
    }

    final boolean isDockedStack() {
        return mStackId == DOCKED_STACK_ID;
    }

    final boolean isPinnedStack() {
        return mStackId == PINNED_STACK_ID;
    }

    final boolean isOnHomeDisplay() {
        return isAttached() &&
                mActivityContainer.mActivityDisplay.mDisplayId == DEFAULT_DISPLAY;
    }

    void moveToFront(String reason) {
        moveToFront(reason, null);
    }

    /**
     * @param reason The reason for moving the stack to the front.
     * @param task If non-null, the task will be moved to the top of the stack.
     * */
    void moveToFront(String reason, TaskRecord task) {
        if (!isAttached()) {
            return;
        }

        mStacks.remove(this);
        int addIndex = mStacks.size();

        if (addIndex > 0) {
            final ActivityStack topStack = mStacks.get(addIndex - 1);
            if (StackId.isAlwaysOnTop(topStack.mStackId) && topStack != this) {
                // If the top stack is always on top, we move this stack just below it.
                addIndex--;
            }
        }

        mStacks.add(addIndex, this);

        // TODO(multi-display): Needs to also work if focus is moving to the non-home display.
        if (isOnHomeDisplay()) {
            mStackSupervisor.setFocusStackUnchecked(reason, this);
        }
        if (task != null) {
            insertTaskAtTop(task, null);
        } else {
            task = topTask();
        }
        if (task != null) {
            mWindowManager.moveTaskToTop(task.taskId);
        }
    }

    boolean isFocusable() {
        if (StackId.canReceiveKeys(mStackId)) {
            return true;
        }
        // The stack isn't focusable. See if its top activity is focusable to force focus on the
        // stack.
        final ActivityRecord r = topRunningActivityLocked();
        return r != null && r.isFocusable();
    }

    final boolean isAttached() {
        return mStacks != null;
    }

    /**
     * Returns the top activity in any existing task matching the given Intent in the input result.
     * Returns null if no such task is found.
     */
    void findTaskLocked(ActivityRecord target, FindTaskResult result) {
        Intent intent = target.intent;
        ActivityInfo info = target.info;
        ComponentName cls = intent.getComponent();
        if (info.targetActivity != null) {
            cls = new ComponentName(info.packageName, info.targetActivity);
        }
        final int userId = UserHandle.getUserId(info.applicationInfo.uid);
        boolean isDocument = intent != null & intent.isDocument();
        // If documentData is non-null then it must match the existing task data.
        Uri documentData = isDocument ? intent.getData() : null;

        if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Looking for task of " + target + " in " + this);
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            if (task.voiceSession != null) {
                // We never match voice sessions; those always run independently.
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": voice session");
                continue;
            }
            if (task.userId != userId) {
                // Looking for a different task.
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": different user");
                continue;
            }
            final ActivityRecord r = task.getTopActivity();
            if (r == null || r.finishing || r.userId != userId ||
                    r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": mismatch root " + r);
                continue;
            }
            if (r.mActivityType != target.mActivityType) {
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": mismatch activity type");
                continue;
            }

            final Intent taskIntent = task.intent;
            final Intent affinityIntent = task.affinityIntent;
            final boolean taskIsDocument;
            final Uri taskDocumentData;
            if (taskIntent != null && taskIntent.isDocument()) {
                taskIsDocument = true;
                taskDocumentData = taskIntent.getData();
            } else if (affinityIntent != null && affinityIntent.isDocument()) {
                taskIsDocument = true;
                taskDocumentData = affinityIntent.getData();
            } else {
                taskIsDocument = false;
                taskDocumentData = null;
            }

            if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Comparing existing cls="
                    + taskIntent.getComponent().flattenToShortString()
                    + "/aff=" + r.task.rootAffinity + " to new cls="
                    + intent.getComponent().flattenToShortString() + "/aff=" + info.taskAffinity);
            // TODO Refactor to remove duplications. Check if logic can be simplified.
            if (taskIntent != null && taskIntent.getComponent() != null &&
                    taskIntent.getComponent().compareTo(cls) == 0 &&
                    Objects.equals(documentData, taskDocumentData)) {
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching class!");
                //dump();
                if (DEBUG_TASKS) Slog.d(TAG_TASKS,
                        "For Intent " + intent + " bringing to top: " + r.intent);
                result.r = r;
                result.matchedByRootAffinity = false;
                break;
            } else if (affinityIntent != null && affinityIntent.getComponent() != null &&
                    affinityIntent.getComponent().compareTo(cls) == 0 &&
                    Objects.equals(documentData, taskDocumentData)) {
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching class!");
                //dump();
                if (DEBUG_TASKS) Slog.d(TAG_TASKS,
                        "For Intent " + intent + " bringing to top: " + r.intent);
                result.r = r;
                result.matchedByRootAffinity = false;
                break;
            } else if (!isDocument && !taskIsDocument
                    && result.r == null && task.canMatchRootAffinity()) {
                if (task.rootAffinity.equals(target.taskAffinity)) {
                    if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching affinity candidate!");
                    // It is possible for multiple tasks to have the same root affinity especially
                    // if they are in separate stacks. We save off this candidate, but keep looking
                    // to see if there is a better candidate.
                    result.r = r;
                    result.matchedByRootAffinity = true;
                }
            } else if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Not a match: " + task);
        }
    }

    /**
     * Returns the first activity (starting from the top of the stack) that
     * is the same as the given activity.  Returns null if no such activity
     * is found.
     */
    ActivityRecord findActivityLocked(Intent intent, ActivityInfo info,
                                      boolean compareIntentFilters) {
        ComponentName cls = intent.getComponent();
        if (info.targetActivity != null) {
            cls = new ComponentName(info.packageName, info.targetActivity);
        }
        final int userId = UserHandle.getUserId(info.applicationInfo.uid);

        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            final boolean notCurrentUserTask =
                    !mStackSupervisor.isCurrentProfileLocked(task.userId);
            final ArrayList<ActivityRecord> activities = task.mActivities;

            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                ActivityRecord r = activities.get(activityNdx);
                if (notCurrentUserTask && (r.info.flags & FLAG_SHOW_FOR_ALL_USERS) == 0) {
                    continue;
                }
                if (!r.finishing && r.userId == userId) {
                    if (compareIntentFilters) {
                        if (r.intent.filterEquals(intent)) {
                            return r;
                        }
                    } else {
                        if (r.intent.getComponent().equals(cls)) {
                            return r;
                        }
                    }
                }
            }
        }

        return null;
    }

    /*
     * Move the activities around in the stack to bring a user to the foreground.
     */
    final void switchUserLocked(int userId) {
        if (mCurrentUser == userId) {
            return;
        }
        mCurrentUser = userId;

        // Move userId's tasks to the top.
        int index = mTaskHistory.size();
        for (int i = 0; i < index; ) {
            final TaskRecord task = mTaskHistory.get(i);

            // NOTE: If {@link TaskRecord#topRunningActivityLocked} return is not null then it is
            // okay to show the activity when locked.
            if (mStackSupervisor.isCurrentProfileLocked(task.userId)
                    || task.topRunningActivityLocked() != null) {
                if (DEBUG_TASKS) Slog.d(TAG_TASKS, "switchUserLocked: stack=" + getStackId() +
                        " moving " + task + " to top");
                mTaskHistory.remove(i);
                mTaskHistory.add(task);
                --index;
                // Use same value for i.
            } else {
                ++i;
            }
        }
        if (VALIDATE_TOKENS) {
            validateAppTokensLocked();
        }
    }

    void minimalResumeActivityLocked(ActivityRecord r) {
        r.state = ActivityState.RESUMED;
        if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to RESUMED: " + r + " (starting new instance)"
                + " callers=" + Debug.getCallers(5));
        mResumedActivity = r;
        r.task.touchActiveTime();
        mRecentTasks.addLocked(r.task);
        completeResumeLocked(r);
        mStackSupervisor.checkReadyForSleepLocked();
        setLaunchTime(r);
        if (DEBUG_SAVED_STATE) Slog.i(TAG_SAVED_STATE,
                "Launch completed; removing icicle of " + r.icicle);
    }

    void addRecentActivityLocked(ActivityRecord r) {
        if (r != null) {
            mRecentTasks.addLocked(r.task);
            r.task.touchActiveTime();
        }
    }

    private void startLaunchTraces(String packageName) {
        if (mFullyDrawnStartTime != 0)  {
            Trace.asyncTraceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER, "drawing", 0);
        }
        Trace.asyncTraceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "launching: " + packageName, 0);
        Trace.asyncTraceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "drawing", 0);
    }

    private void stopFullyDrawnTraceIfNeeded() {
        if (mFullyDrawnStartTime != 0 && mLaunchStartTime == 0) {
            Trace.asyncTraceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER, "drawing", 0);
            mFullyDrawnStartTime = 0;
        }
    }

    void setLaunchTime(ActivityRecord r) {
        if (r.displayStartTime == 0) {
            r.fullyDrawnStartTime = r.displayStartTime = SystemClock.uptimeMillis();
            if (mLaunchStartTime == 0) {
                startLaunchTraces(r.packageName);
                mLaunchStartTime = mFullyDrawnStartTime = r.displayStartTime;
            }
        } else if (mLaunchStartTime == 0) {
            startLaunchTraces(r.packageName);
            mLaunchStartTime = mFullyDrawnStartTime = SystemClock.uptimeMillis();
        }
    }

    void clearLaunchTime(ActivityRecord r) {
        // Make sure that there is no activity waiting for this to launch.
        if (mStackSupervisor.mWaitingActivityLaunched.isEmpty()) {
            r.displayStartTime = r.fullyDrawnStartTime = 0;
        } else {
            mStackSupervisor.removeTimeoutsForActivityLocked(r);
            mStackSupervisor.scheduleIdleTimeoutLocked(r);
        }
    }

    void awakeFromSleepingLocked() {
        // Ensure activities are no longer sleeping.
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                activities.get(activityNdx).setSleeping(false);
            }
        }
        if (mPausingActivity != null) {
            Slog.d(TAG, "awakeFromSleepingLocked: previously pausing activity didn't pause");
            activityPausedLocked(mPausingActivity.appToken, true);
        }
    }

    void updateActivityApplicationInfoLocked(ApplicationInfo aInfo) {
        final String packageName = aInfo.packageName;
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final List<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                if (packageName.equals(activities.get(activityNdx).packageName)) {
                    activities.get(activityNdx).info.applicationInfo = aInfo;
                }
            }
        }
    }

    /**
     * @return true if something must be done before going to sleep.
     */
    boolean checkReadyForSleepLocked() {
        if (mResumedActivity != null) {
            // Still have something resumed; can't sleep until it is paused.
            if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Sleep needs to pause " + mResumedActivity);
            if (DEBUG_USER_LEAVING) Slog.v(TAG_USER_LEAVING,
                    "Sleep => pause with userLeaving=false");
            startPausingLocked(false, true, null, false);
            return true;
        }
        if (mPausingActivity != null) {
            // Still waiting for something to pause; can't sleep yet.
            if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Sleep still waiting to pause " + mPausingActivity);
            return true;
        }

        if (hasVisibleBehindActivity()) {
            // Stop visible behind activity before going to sleep.
            final ActivityRecord r = getVisibleBehindActivity();
            mStackSupervisor.mStoppingActivities.add(r);
            if (DEBUG_STATES) Slog.v(TAG_STATES, "Sleep still waiting to stop visible behind " + r);
            return true;
        }

        return false;
    }

    void goToSleep() {
        ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);

        // Make sure any paused or stopped but visible activities are now sleeping.
        // This ensures that the activity's onStop() is called.
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                if (r.state == ActivityState.STOPPING || r.state == ActivityState.STOPPED
                        || r.state == ActivityState.PAUSED || r.state == ActivityState.PAUSING) {
                    r.setSleeping(true);
                }
            }
        }
    }

    public final Bitmap screenshotActivitiesLocked(ActivityRecord who) {
        if (DEBUG_SCREENSHOTS) Slog.d(TAG_SCREENSHOTS, "screenshotActivitiesLocked: " + who);
        if (who.noDisplay) {
            if (DEBUG_SCREENSHOTS) Slog.d(TAG_SCREENSHOTS, "\tNo display");
            return null;
        }

        if (isHomeStack()) {
            // This is an optimization -- since we never show Home or Recents within Recents itself,
            // we can just go ahead and skip taking the screenshot if this is the home stack.
            if (DEBUG_SCREENSHOTS) Slog.d(TAG_SCREENSHOTS, "\tHome stack");
            return null;
        }

        int w = mService.mThumbnailWidth;
        int h = mService.mThumbnailHeight;

        if (w <= 0) {
            Slog.e(TAG, "\tInvalid thumbnail dimensions: " + w + "x" + h);
            return null;
        }

        if (mStackId == DOCKED_STACK_ID && mStackSupervisor.mIsDockMinimized) {
            // When the docked stack is minimized its app windows are cropped significantly so any
            // screenshot taken will not display the apps contain. So, we avoid taking a screenshot
            // in that case.
            if (DEBUG_SCREENSHOTS) Slog.e(TAG, "\tIn minimized docked stack");
            return null;
        }

        float scale = 1f;
        if (DEBUG_SCREENSHOTS) Slog.d(TAG_SCREENSHOTS, "\tTaking screenshot");

        // When this flag is set, we currently take the fullscreen screenshot of the activity but
        // scaled to half the size. This gives us a "good-enough" fullscreen thumbnail to use within
        // SystemUI while keeping memory usage low.
        if (TAKE_FULLSCREEN_SCREENSHOTS) {
            w = h = -1;
            scale = mService.mFullscreenThumbnailScale;
        }

        return mWindowManager.screenshotApplications(who.appToken, DEFAULT_DISPLAY, w, h, scale);
    }

    /**
     * Start pausing the currently resumed activity.  It is an error to call this if there
     * is already an activity being paused or there is no resumed activity.
     *
     * @param userLeaving True if this should result in an onUserLeaving to the current activity.
     * @param uiSleeping True if this is happening with the user interface going to sleep (the
     * screen turning off).
     * @param resuming The activity we are currently trying to resume or null if this is not being
     *                 called as part of resuming the top activity, so we shouldn't try to instigate
     *                 a resume here if not null.
     * @param dontWait True if the caller does not want to wait for the pause to complete.  If
     * set to true, we will immediately complete the pause here before returning.
     * @return Returns true if an activity now is in the PAUSING state, and we are waiting for
     * it to tell us when it is done.
     */
    final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping,
            ActivityRecord resuming, boolean dontWait) {
        if (mPausingActivity != null) {
            Slog.wtf(TAG, "Going to pause when pause is already pending for " + mPausingActivity
                    + " state=" + mPausingActivity.state);
            if (!mService.isSleepingLocked()) {
                // Avoid recursion among check for sleep and complete pause during sleeping.
                // Because activity will be paused immediately after resume, just let pause
                // be completed by the order of activity paused from clients.
                completePauseLocked(false, resuming);
            }
        }
        ActivityRecord prev = mResumedActivity;
        if (prev == null) {
            if (resuming == null) {
                Slog.wtf(TAG, "Trying to pause when nothing is resumed");
                mStackSupervisor.resumeFocusedStackTopActivityLocked();
            }
            return false;
        }

        if (mActivityContainer.mParentActivity == null) {
            // Top level stack, not a child. Look for child stacks.
            mStackSupervisor.pauseChildStacks(prev, userLeaving, uiSleeping, resuming, dontWait);
        }

        if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to PAUSING: " + prev);
        else if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Start pausing: " + prev);
        mResumedActivity = null;
        mPausingActivity = prev;
        mLastPausedActivity = prev;
        mLastNoHistoryActivity = (prev.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_HISTORY) != 0
                || (prev.info.flags & ActivityInfo.FLAG_NO_HISTORY) != 0 ? prev : null;
        prev.state = ActivityState.PAUSING;
        prev.task.touchActiveTime();
        clearLaunchTime(prev);
        final ActivityRecord next = mStackSupervisor.topRunningActivityLocked();
        if (mService.mHasRecents
                && (next == null || next.noDisplay || next.task != prev.task || uiSleeping)) {
            prev.mUpdateTaskThumbnailWhenHidden = true;
        }
        stopFullyDrawnTraceIfNeeded();

        mService.updateCpuStats();

        if (prev.app != null && prev.app.thread != null) {
            if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Enqueueing pending pause: " + prev);
            try {
                EventLog.writeEvent(EventLogTags.AM_PAUSE_ACTIVITY,
                        prev.userId, System.identityHashCode(prev),
                        prev.shortComponentName);
                mService.updateUsageStats(prev, false);
                prev.app.thread.schedulePauseActivity(prev.appToken, prev.finishing,
                        userLeaving, prev.configChangeFlags, dontWait);
            } catch (Exception e) {
                // Ignore exception, if process died other code will cleanup.
                Slog.w(TAG, "Exception thrown during pause", e);
                mPausingActivity = null;
                mLastPausedActivity = null;
                mLastNoHistoryActivity = null;
            }
        } else {
            mPausingActivity = null;
            mLastPausedActivity = null;
            mLastNoHistoryActivity = null;
        }

        // If we are not going to sleep, we want to ensure the device is
        // awake until the next activity is started.
        if (!uiSleeping && !mService.isSleepingOrShuttingDownLocked()) {
            mStackSupervisor.acquireLaunchWakelock();
        }

        if (mPausingActivity != null) {
            // Have the window manager pause its key dispatching until the new
            // activity has started.  If we're pausing the activity just because
            // the screen is being turned off and the UI is sleeping, don't interrupt
            // key dispatch; the same activity will pick it up again on wakeup.
            if (!uiSleeping) {
                prev.pauseKeyDispatchingLocked();
            } else if (DEBUG_PAUSE) {
                 Slog.v(TAG_PAUSE, "Key dispatch not paused for screen off");
            }

            if (dontWait) {
                // If the caller said they don't want to wait for the pause, then complete
                // the pause now.
                completePauseLocked(false, resuming);
                return false;

            } else {
                // Schedule a pause timeout in case the app doesn't respond.
                // We don't give it much time because this directly impacts the
                // responsiveness seen by the user.
                Message msg = mHandler.obtainMessage(PAUSE_TIMEOUT_MSG);
                msg.obj = prev;
                prev.pauseTime = SystemClock.uptimeMillis();
                mHandler.sendMessageDelayed(msg, PAUSE_TIMEOUT);
                if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Waiting for pause to complete...");
                return true;
            }

        } else {
            // This activity failed to schedule the
            // pause, so just treat it as being paused now.
            if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Activity not running, resuming next.");
            if (resuming == null) {
                mStackSupervisor.resumeFocusedStackTopActivityLocked();
            }
            return false;
        }
    }

    final void activityPausedLocked(IBinder token, boolean timeout) {
        if (DEBUG_PAUSE) Slog.v(TAG_PAUSE,
            "Activity paused: token=" + token + ", timeout=" + timeout);

        final ActivityRecord r = isInStackLocked(token);
        if (r != null) {
            mHandler.removeMessages(PAUSE_TIMEOUT_MSG, r);
            if (mPausingActivity == r) {
                if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to PAUSED: " + r
                        + (timeout ? " (due to timeout)" : " (pause complete)"));
                completePauseLocked(true, null);
                return;
            } else {
                EventLog.writeEvent(EventLogTags.AM_FAILED_TO_PAUSE,
                        r.userId, System.identityHashCode(r), r.shortComponentName,
                        mPausingActivity != null
                            ? mPausingActivity.shortComponentName : "(none)");
                if (r.state == ActivityState.PAUSING) {
                    r.state = ActivityState.PAUSED;
                    if (r.finishing) {
                        if (DEBUG_PAUSE) Slog.v(TAG,
                                "Executing finish of failed to pause activity: " + r);
                        finishCurrentActivityLocked(r, FINISH_AFTER_VISIBLE, false);
                    }
                }
            }
        }
        mStackSupervisor.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
    }

    final void activityResumedLocked(IBinder token) {
        final ActivityRecord r = ActivityRecord.forTokenLocked(token);
        if (DEBUG_SAVED_STATE) Slog.i(TAG_STATES, "Resumed activity; dropping state of: " + r);
        r.icicle = null;
        r.haveState = false;
    }

    final void activityStoppedLocked(ActivityRecord r, Bundle icicle,
            PersistableBundle persistentState, CharSequence description) {
        if (r.state != ActivityState.STOPPING) {
            Slog.i(TAG, "Activity reported stop, but no longer stopping: " + r);
            mHandler.removeMessages(STOP_TIMEOUT_MSG, r);
            return;
        }
        if (persistentState != null) {
            r.persistentState = persistentState;
            mService.notifyTaskPersisterLocked(r.task, false);
        }
        if (DEBUG_SAVED_STATE) Slog.i(TAG_SAVED_STATE, "Saving icicle of " + r + ": " + icicle);
        if (icicle != null) {
            // If icicle is null, this is happening due to a timeout, so we
            // haven't really saved the state.
            r.icicle = icicle;
            r.haveState = true;
            r.launchCount = 0;
            r.updateThumbnailLocked(null, description);
        }
        if (!r.stopped) {
            if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to STOPPED: " + r + " (stop complete)");
            mHandler.removeMessages(STOP_TIMEOUT_MSG, r);
            r.stopped = true;
            r.state = ActivityState.STOPPED;

            mWindowManager.notifyAppStopped(r.appToken);

            if (getVisibleBehindActivity() == r) {
                mStackSupervisor.requestVisibleBehindLocked(r, false);
            }
            if (r.finishing) {
                r.clearOptionsLocked();
            } else {
                if (r.deferRelaunchUntilPaused) {
                    destroyActivityLocked(r, true, "stop-config");
                    mStackSupervisor.resumeFocusedStackTopActivityLocked();
                } else {
                    mStackSupervisor.updatePreviousProcessLocked(r);
                }
            }
        }
    }

    private void completePauseLocked(boolean resumeNext, ActivityRecord resuming) {
        ActivityRecord prev = mPausingActivity;
        if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Complete pause: " + prev);

        if (prev != null) {
            final boolean wasStopping = prev.state == ActivityState.STOPPING;
            prev.state = ActivityState.PAUSED;
            if (prev.finishing) {
                if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Executing finish of activity: " + prev);
                prev = finishCurrentActivityLocked(prev, FINISH_AFTER_VISIBLE, false);
            } else if (prev.app != null) {
                if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Enqueue pending stop if needed: " + prev
                        + " wasStopping=" + wasStopping + " visible=" + prev.visible);
                if (mStackSupervisor.mWaitingVisibleActivities.remove(prev)) {
                    if (DEBUG_SWITCH || DEBUG_PAUSE) Slog.v(TAG_PAUSE,
                            "Complete pause, no longer waiting: " + prev);
                }
                if (prev.deferRelaunchUntilPaused) {
                    // Complete the deferred relaunch that was waiting for pause to complete.
                    if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Re-launching after pause: " + prev);
                    relaunchActivityLocked(prev, prev.configChangeFlags, false,
                            prev.preserveWindowOnDeferredRelaunch);
                } else if (wasStopping) {
                    // We are also stopping, the stop request must have gone soon after the pause.
                    // We can't clobber it, because the stop confirmation will not be handled.
                    // We don't need to schedule another stop, we only need to let it happen.
                    prev.state = ActivityState.STOPPING;
                } else if ((!prev.visible && !hasVisibleBehindActivity())
                        || mService.isSleepingOrShuttingDownLocked()) {
                    // If we were visible then resumeTopActivities will release resources before
                    // stopping.
                    addToStopping(prev, true /* immediate */);
                }
            } else {
                if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "App died during pause, not stopping: " + prev);
                prev = null;
            }
            // It is possible the activity was freezing the screen before it was paused.
            // In that case go ahead and remove the freeze this activity has on the screen
            // since it is no longer visible.
            if (prev != null) {
                prev.stopFreezingScreenLocked(true /*force*/);
            }
            mPausingActivity = null;
        }

        if (resumeNext) {
            final ActivityStack topStack = mStackSupervisor.getFocusedStack();
            if (!mService.isSleepingOrShuttingDownLocked()) {
                mStackSupervisor.resumeFocusedStackTopActivityLocked(topStack, prev, null);
            } else {
                mStackSupervisor.checkReadyForSleepLocked();
                ActivityRecord top = topStack.topRunningActivityLocked();
                if (top == null || (prev != null && top != prev)) {
                    // If there are no more activities available to run, do resume anyway to start
                    // something. Also if the top activity on the stack is not the just paused
                    // activity, we need to go ahead and resume it to ensure we complete an
                    // in-flight app switch.
                    mStackSupervisor.resumeFocusedStackTopActivityLocked();
                }
            }
        }

        if (prev != null) {
            prev.resumeKeyDispatchingLocked();

            if (prev.app != null && prev.cpuTimeAtResume > 0
                    && mService.mBatteryStatsService.isOnBattery()) {
                long diff = mService.mProcessCpuTracker.getCpuTimeForPid(prev.app.pid)
                        - prev.cpuTimeAtResume;
                if (diff > 0) {
                    BatteryStatsImpl bsi = mService.mBatteryStatsService.getActiveStatistics();
                    synchronized (bsi) {
                        BatteryStatsImpl.Uid.Proc ps =
                                bsi.getProcessStatsLocked(prev.info.applicationInfo.uid,
                                        prev.info.packageName);
                        if (ps != null) {
                            ps.addForegroundTimeLocked(diff);
                        }
                    }
                }
            }
            prev.cpuTimeAtResume = 0; // reset it
        }

        // Notify when the task stack has changed, but only if visibilities changed (not just
        // focus). Also if there is an active pinned stack - we always want to notify it about
        // task stack changes, because its positioning may depend on it.
        if (mStackSupervisor.mAppVisibilitiesChangedSinceLastPause
                || mService.mStackSupervisor.getStack(PINNED_STACK_ID) != null) {
            mService.notifyTaskStackChangedLocked();
            mStackSupervisor.mAppVisibilitiesChangedSinceLastPause = false;
        }

        mStackSupervisor.ensureActivitiesVisibleLocked(resuming, 0, !PRESERVE_WINDOWS);
    }

    private void addToStopping(ActivityRecord r, boolean immediate) {
        if (!mStackSupervisor.mStoppingActivities.contains(r)) {
            mStackSupervisor.mStoppingActivities.add(r);
        }

        // If we already have a few activities waiting to stop, then give up
        // on things going idle and start clearing them out. Or if r is the
        // last of activity of the last task the stack will be empty and must
        // be cleared immediately.
        boolean forceIdle = mStackSupervisor.mStoppingActivities.size() > MAX_STOPPING_TO_FORCE
                || (r.frontOfTask && mTaskHistory.size() <= 1);

        if (immediate || forceIdle) {
            if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Scheduling idle now: forceIdle="
                    + forceIdle + "immediate=" + immediate);
            mStackSupervisor.scheduleIdleLocked();
        } else {
            mStackSupervisor.checkReadyForSleepLocked();
        }
    }

    /**
     * Once we know that we have asked an application to put an activity in
     * the resumed state (either by launching it or explicitly telling it),
     * this function updates the rest of our state to match that fact.
     */
    private void completeResumeLocked(ActivityRecord next) {
        next.visible = true;
        next.idle = false;
        next.results = null;
        next.newIntents = null;
        next.stopped = false;

        if (next.isHomeActivity()) {
            ProcessRecord app = next.task.mActivities.get(0).app;
            if (app != null && app != mService.mHomeProcess) {
                mService.mHomeProcess = app;
            }
        }

        if (next.nowVisible) {
            // We won't get a call to reportActivityVisibleLocked() so dismiss lockscreen now.
            mStackSupervisor.reportActivityVisibleLocked(next);
            mStackSupervisor.notifyActivityDrawnForKeyguard();
        }

        // schedule an idle timeout in case the app doesn't do it for us.
        mStackSupervisor.scheduleIdleTimeoutLocked(next);

        mStackSupervisor.reportResumedActivityLocked(next);

        next.resumeKeyDispatchingLocked();
        mNoAnimActivities.clear();

        // Mark the point when the activity is resuming
        // TODO: To be more accurate, the mark should be before the onCreate,
        //       not after the onResume. But for subsequent starts, onResume is fine.
        if (next.app != null) {
            next.cpuTimeAtResume = mService.mProcessCpuTracker.getCpuTimeForPid(next.app.pid);
        } else {
            next.cpuTimeAtResume = 0; // Couldn't get the cpu time of process
        }

        next.returningOptions = null;

        if (getVisibleBehindActivity() == next) {
            // When resuming an activity, require it to call requestVisibleBehind() again.
            setVisibleBehindActivity(null);
        }
    }

    private void setVisible(ActivityRecord r, boolean visible) {
        r.visible = visible;
        if (!visible && r.mUpdateTaskThumbnailWhenHidden) {
            r.updateThumbnailLocked(r.task.stack.screenshotActivitiesLocked(r), null);
            r.mUpdateTaskThumbnailWhenHidden = false;
        }
        mWindowManager.setAppVisibility(r.appToken, visible);
        final ArrayList<ActivityContainer> containers = r.mChildContainers;
        for (int containerNdx = containers.size() - 1; containerNdx >= 0; --containerNdx) {
            ActivityContainer container = containers.get(containerNdx);
            container.setVisible(visible);
        }
        mStackSupervisor.mAppVisibilitiesChangedSinceLastPause = true;
    }

    // Find the first visible activity above the passed activity and if it is translucent return it
    // otherwise return null;
    ActivityRecord findNextTranslucentActivity(ActivityRecord r) {
        TaskRecord task = r.task;
        if (task == null) {
            return null;
        }

        ActivityStack stack = task.stack;
        if (stack == null) {
            return null;
        }

        int stackNdx = mStacks.indexOf(stack);

        ArrayList<TaskRecord> tasks = stack.mTaskHistory;
        int taskNdx = tasks.indexOf(task);

        ArrayList<ActivityRecord> activities = task.mActivities;
        int activityNdx = activities.indexOf(r) + 1;

        final int numStacks = mStacks.size();
        while (stackNdx < numStacks) {
            final ActivityStack historyStack = mStacks.get(stackNdx);
            tasks = historyStack.mTaskHistory;
            final int numTasks = tasks.size();
            while (taskNdx < numTasks) {
                final TaskRecord currentTask = tasks.get(taskNdx);
                activities = currentTask.mActivities;
                final int numActivities = activities.size();
                while (activityNdx < numActivities) {
                    final ActivityRecord activity = activities.get(activityNdx);
                    if (!activity.finishing) {
                        return historyStack.mFullscreen
                                && currentTask.mFullscreen && activity.fullscreen ? null : activity;
                    }
                    ++activityNdx;
                }
                activityNdx = 0;
                ++taskNdx;
            }
            taskNdx = 0;
            ++stackNdx;
        }

        return null;
    }

    ActivityStack getNextFocusableStackLocked() {
        ArrayList<ActivityStack> stacks = mStacks;
        final ActivityRecord parent = mActivityContainer.mParentActivity;
        if (parent != null) {
            stacks = parent.task.stack.mStacks;
        }
        if (stacks != null) {
            for (int i = stacks.size() - 1; i >= 0; --i) {
                ActivityStack stack = stacks.get(i);
                if (stack != this && stack.isFocusable()
                        && stack.getStackVisibilityLocked(null) != STACK_INVISIBLE) {
                    return stack;
                }
            }
        }
        return null;
    }

    /** Returns true if the stack contains a fullscreen task. */
    private boolean hasFullscreenTask() {
        for (int i = mTaskHistory.size() - 1; i >= 0; --i) {
            final TaskRecord task = mTaskHistory.get(i);
            if (task.mFullscreen) {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns true if the stack is translucent and can have other contents visible behind it if
     * needed. A stack is considered translucent if it don't contain a visible or
     * starting (about to be visible) activity that is fullscreen (opaque).
     * @param starting The currently starting activity or null if there is none.
     * @param stackBehindId The id of the stack directly behind this one.
     */
    private boolean isStackTranslucent(ActivityRecord starting, int stackBehindId) {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            final ArrayList<ActivityRecord> activities = task.mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);

                if (r.finishing) {
                    // We don't factor in finishing activities when determining translucency since
                    // they will be gone soon.
                    continue;
                }

                if (!r.visible && r != starting) {
                    // Also ignore invisible activities that are not the currently starting
                    // activity (about to be visible).
                    continue;
                }

                if (r.fullscreen) {
                    // Stack isn't translucent if it has at least one fullscreen activity
                    // that is visible.
                    return false;
                }

                if (!isHomeStack() && r.frontOfTask
                        && task.isOverHomeStack() && stackBehindId != HOME_STACK_ID) {
                    // Stack isn't translucent if it's top activity should have the home stack
                    // behind it and the stack currently behind it isn't the home stack.
                    return false;
                }
            }
        }
        return true;
    }

    /**
     * Returns stack's visibility: {@link #STACK_INVISIBLE}, {@link #STACK_VISIBLE} or
     * {@link #STACK_VISIBLE_ACTIVITY_BEHIND}.
     * @param starting The currently starting activity or null if there is none.
     */
    int getStackVisibilityLocked(ActivityRecord starting) {
        if (!isAttached()) {
            return STACK_INVISIBLE;
        }

        if (mStackSupervisor.isFrontStack(this) || mStackSupervisor.isFocusedStack(this)) {
            return STACK_VISIBLE;
        }

        final int stackIndex = mStacks.indexOf(this);

        if (stackIndex == mStacks.size() - 1) {
            Slog.wtf(TAG,
                    "Stack=" + this + " isn't front stack but is at the top of the stack list");
            return STACK_INVISIBLE;
        }

        final ActivityStack focusedStack = mStackSupervisor.getFocusedStack();
        final int focusedStackId = focusedStack.mStackId;

        if (mStackId == FULLSCREEN_WORKSPACE_STACK_ID
                && hasVisibleBehindActivity() && focusedStackId == HOME_STACK_ID
                && !focusedStack.topActivity().fullscreen) {
            // The fullscreen stack should be visible if it has a visible behind activity behind
            // the home stack that is translucent.
            return STACK_VISIBLE_ACTIVITY_BEHIND;
        }

        if (mStackId == DOCKED_STACK_ID) {
            // Docked stack is always visible, except in the case where the top running activity
            // task in the focus stack doesn't support any form of resizing but we show it for the
            // home task even though it's not resizable.
            final ActivityRecord r = focusedStack.topRunningActivityLocked();
            final TaskRecord task = r != null ? r.task : null;
            return task == null || task.canGoInDockedStack() || task.isHomeTask() ? STACK_VISIBLE
                    : STACK_INVISIBLE;
        }

        // Find the first stack behind focused stack that actually got something visible.
        int stackBehindFocusedIndex = mStacks.indexOf(focusedStack) - 1;
        while (stackBehindFocusedIndex >= 0 &&
                mStacks.get(stackBehindFocusedIndex).topRunningActivityLocked() == null) {
            stackBehindFocusedIndex--;
        }
        if ((focusedStackId == DOCKED_STACK_ID || focusedStackId == PINNED_STACK_ID)
                && stackIndex == stackBehindFocusedIndex) {
            // Stacks directly behind the docked or pinned stack are always visible.
            return STACK_VISIBLE;
        }

        final int stackBehindFocusedId = (stackBehindFocusedIndex >= 0)
                ? mStacks.get(stackBehindFocusedIndex).mStackId : INVALID_STACK_ID;

        if (focusedStackId == FULLSCREEN_WORKSPACE_STACK_ID
                && focusedStack.isStackTranslucent(starting, stackBehindFocusedId)) {
            // Stacks behind the fullscreen stack with a translucent activity are always
            // visible so they can act as a backdrop to the translucent activity.
            // For example, dialog activities
            if (stackIndex == stackBehindFocusedIndex) {
                return STACK_VISIBLE;
            }
            if (stackBehindFocusedIndex >= 0) {
                if ((stackBehindFocusedId == DOCKED_STACK_ID
                        || stackBehindFocusedId == PINNED_STACK_ID)
                        && stackIndex == (stackBehindFocusedIndex - 1)) {
                    // The stack behind the docked or pinned stack is also visible so we can have a
                    // complete backdrop to the translucent activity when the docked stack is up.
                    return STACK_VISIBLE;
                }
            }
        }

        if (StackId.isStaticStack(mStackId)) {
            // Visibility of any static stack should have been determined by the conditions above.
            return STACK_INVISIBLE;
        }

        for (int i = stackIndex + 1; i < mStacks.size(); i++) {
            final ActivityStack stack = mStacks.get(i);

            if (!stack.mFullscreen && !stack.hasFullscreenTask()) {
                continue;
            }

            if (!StackId.isDynamicStacksVisibleBehindAllowed(stack.mStackId)) {
                // These stacks can't have any dynamic stacks visible behind them.
                return STACK_INVISIBLE;
            }

            if (!stack.isStackTranslucent(starting, INVALID_STACK_ID)) {
                return STACK_INVISIBLE;
            }
        }

        return STACK_VISIBLE;
    }

    final int rankTaskLayers(int baseLayer) {
        int layer = 0;
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            ActivityRecord r = task.topRunningActivityLocked();
            if (r == null || r.finishing || !r.visible) {
                task.mLayerRank = -1;
            } else {
                task.mLayerRank = baseLayer + layer++;
            }
        }
        return layer;
    }

    /**
     * Make sure that all activities that need to be visible (that is, they
     * currently can be seen by the user) actually are.
     */
    final void ensureActivitiesVisibleLocked(ActivityRecord starting, int configChanges,
            boolean preserveWindows) {
        ActivityRecord top = topRunningActivityLocked();
        if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "ensureActivitiesVisible behind " + top
                + " configChanges=0x" + Integer.toHexString(configChanges));
        if (top != null) {
            checkTranslucentActivityWaiting(top);
        }

        // If the top activity is not fullscreen, then we need to
        // make sure any activities under it are now visible.
        boolean aboveTop = top != null;
        final int stackVisibility = getStackVisibilityLocked(starting);
        final boolean stackInvisible = stackVisibility != STACK_VISIBLE;
        final boolean stackVisibleBehind = stackVisibility == STACK_VISIBLE_ACTIVITY_BEHIND;
        boolean behindFullscreenActivity = stackInvisible;
        boolean resumeNextActivity = mStackSupervisor.isFocusedStack(this)
                && (isInStackLocked(starting) == null);
        boolean behindTranslucentActivity = false;
        final ActivityRecord visibleBehind = getVisibleBehindActivity();
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            final ArrayList<ActivityRecord> activities = task.mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                if (r.finishing) {
                    // Normally the screenshot will be taken in makeInvisible(). When an activity
                    // is finishing, we no longer change its visibility, but we still need to take
                    // the screenshots if startPausingLocked decided it should be taken.
                    if (r.mUpdateTaskThumbnailWhenHidden) {
                        r.updateThumbnailLocked(screenshotActivitiesLocked(r), null);
                        r.mUpdateTaskThumbnailWhenHidden = false;
                    }
                    continue;
                }
                final boolean isTop = r == top;
                if (aboveTop && !isTop) {
                    continue;
                }
                aboveTop = false;

                if (shouldBeVisible(r, behindTranslucentActivity, stackVisibleBehind,
                        visibleBehind, behindFullscreenActivity)) {
                    if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Make visible? " + r
                            + " finishing=" + r.finishing + " state=" + r.state);
                    // First: if this is not the current activity being started, make
                    // sure it matches the current configuration.
                    if (r != starting) {
                        ensureActivityConfigurationLocked(r, 0, preserveWindows);
                    }

                    if (r.app == null || r.app.thread == null) {
                        if (makeVisibleAndRestartIfNeeded(starting, configChanges, isTop,
                                resumeNextActivity, r)) {
                            if (activityNdx >= activities.size()) {
                                // Record may be removed if its process needs to restart.
                                activityNdx = activities.size() - 1;
                            } else {
                                resumeNextActivity = false;
                            }
                        }
                    } else if (r.visible) {
                        // If this activity is already visible, then there is nothing to do here.
                        if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY,
                                "Skipping: already visible at " + r);

                        if (handleAlreadyVisible(r)) {
                            resumeNextActivity = false;
                        }
                    } else {
                        makeVisibleIfNeeded(starting, r);
                    }
                    // Aggregate current change flags.
                    configChanges |= r.configChangeFlags;
                    behindFullscreenActivity = updateBehindFullscreen(stackInvisible,
                            behindFullscreenActivity, task, r);
                    if (behindFullscreenActivity && !r.fullscreen) {
                        behindTranslucentActivity = true;
                    }
                } else {
                    if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Make invisible? " + r
                            + " finishing=" + r.finishing + " state=" + r.state + " stackInvisible="
                            + stackInvisible + " behindFullscreenActivity="
                            + behindFullscreenActivity + " mLaunchTaskBehind="
                            + r.mLaunchTaskBehind);
                    makeInvisible(r, visibleBehind);
                }
            }
            if (mStackId == FREEFORM_WORKSPACE_STACK_ID) {
                // The visibility of tasks and the activities they contain in freeform stack are
                // determined individually unlike other stacks where the visibility or fullscreen
                // status of an activity in a previous task affects other.
                behindFullscreenActivity = stackVisibility == STACK_INVISIBLE;
            } else if (mStackId == HOME_STACK_ID) {
                if (task.isHomeTask()) {
                    if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Home task: at " + task
                            + " stackInvisible=" + stackInvisible
                            + " behindFullscreenActivity=" + behindFullscreenActivity);
                    // No other task in the home stack should be visible behind the home activity.
                    // Home activities is usually a translucent activity with the wallpaper behind
                    // them. However, when they don't have the wallpaper behind them, we want to
                    // show activities in the next application stack behind them vs. another
                    // task in the home stack like recents.
                    behindFullscreenActivity = true;
                } else if (task.isRecentsTask()
                        && task.getTaskToReturnTo() == APPLICATION_ACTIVITY_TYPE) {
                    if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY,
                            "Recents task returning to app: at " + task
                                    + " stackInvisible=" + stackInvisible
                                    + " behindFullscreenActivity=" + behindFullscreenActivity);
                    // We don't want any other tasks in the home stack visible if the recents
                    // activity is going to be returning to an application activity type.
                    // We do this to preserve the visible order the user used to get into the
                    // recents activity. The recents activity is normally translucent and if it
                    // doesn't have the wallpaper behind it the next activity in the home stack
                    // shouldn't be visible when the home stack is brought to the front to display
                    // the recents activity from an app.
                    behindFullscreenActivity = true;
                }

            }
        }

        if (mTranslucentActivityWaiting != null &&
                mUndrawnActivitiesBelowTopTranslucent.isEmpty()) {
            // Nothing is getting drawn or everything was already visible, don't wait for timeout.
            notifyActivityDrawnLocked(null);
        }
    }

    /** Return true if the input activity should be made visible */
    private boolean shouldBeVisible(ActivityRecord r, boolean behindTranslucentActivity,
            boolean stackVisibleBehind, ActivityRecord visibleBehind,
            boolean behindFullscreenActivity) {

        if (!okToShowLocked(r)) {
            return false;
        }

        // mLaunchingBehind: Activities launching behind are at the back of the task stack
        // but must be drawn initially for the animation as though they were visible.
        final boolean activityVisibleBehind =
                (behindTranslucentActivity || stackVisibleBehind) && visibleBehind == r;

        boolean isVisible =
                !behindFullscreenActivity || r.mLaunchTaskBehind || activityVisibleBehind;

        if (mService.mSupportsLeanbackOnly && isVisible && r.isRecentsActivity()) {
            // On devices that support leanback only (Android TV), Recents activity can only be
            // visible if the home stack is the focused stack or we are in split-screen mode.
            isVisible = mStackSupervisor.getStack(DOCKED_STACK_ID) != null
                    || mStackSupervisor.isFocusedStack(this);
        }

        return isVisible;
    }

    private void checkTranslucentActivityWaiting(ActivityRecord top) {
        if (mTranslucentActivityWaiting != top) {
            mUndrawnActivitiesBelowTopTranslucent.clear();
            if (mTranslucentActivityWaiting != null) {
                // Call the callback with a timeout indication.
                notifyActivityDrawnLocked(null);
                mTranslucentActivityWaiting = null;
            }
            mHandler.removeMessages(TRANSLUCENT_TIMEOUT_MSG);
        }
    }

    private boolean makeVisibleAndRestartIfNeeded(ActivityRecord starting, int configChanges,
            boolean isTop, boolean andResume, ActivityRecord r) {
        // We need to make sure the app is running if it's the top, or it is just made visible from
        // invisible. If the app is already visible, it must have died while it was visible. In this
        // case, we'll show the dead window but will not restart the app. Otherwise we could end up
        // thrashing.
        if (isTop || !r.visible) {
            // This activity needs to be visible, but isn't even running...
            // get it started and resume if no other stack in this stack is resumed.
            if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Start and freeze screen for " + r);
            if (r != starting) {
                r.startFreezingScreenLocked(r.app, configChanges);
            }
            if (!r.visible || r.mLaunchTaskBehind) {
                if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Starting and making visible: " + r);
                setVisible(r, true);
            }
            if (r != starting) {
                mStackSupervisor.startSpecificActivityLocked(r, andResume, false);
                return true;
            }
        }
        return false;
    }

    private void makeInvisible(ActivityRecord r, ActivityRecord visibleBehind) {
        if (!r.visible) {
            if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Already invisible: " + r);
            return;
        }
        // Now for any activities that aren't visible to the user, make sure they no longer are
        // keeping the screen frozen.
        if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Making invisible: " + r + " " + r.state);
        try {
            setVisible(r, false);
            switch (r.state) {
                case STOPPING:
                case STOPPED:
                    if (r.app != null && r.app.thread != null) {
                        if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY,
                                "Scheduling invisibility: " + r);
                        r.app.thread.scheduleWindowVisibility(r.appToken, false);
                    }
                    break;

                case INITIALIZING:
                case RESUMED:
                case PAUSING:
                case PAUSED:
                    // This case created for transitioning activities from
                    // translucent to opaque {@link Activity#convertToOpaque}.
                    if (visibleBehind == r) {
                        releaseBackgroundResources(r);
                    } else {
                        addToStopping(r, true /* immediate */);
                    }
                    break;

                default:
                    break;
            }
        } catch (Exception e) {
            // Just skip on any failure; we'll make it visible when it next restarts.
            Slog.w(TAG, "Exception thrown making hidden: " + r.intent.getComponent(), e);
        }
    }

    private boolean updateBehindFullscreen(boolean stackInvisible, boolean behindFullscreenActivity,
            TaskRecord task, ActivityRecord r) {
        if (r.fullscreen) {
            if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Fullscreen: at " + r
                        + " stackInvisible=" + stackInvisible
                        + " behindFullscreenActivity=" + behindFullscreenActivity);
            // At this point, nothing else needs to be shown in this task.
            behindFullscreenActivity = true;
        } else if (!isHomeStack() && r.frontOfTask && task.isOverHomeStack()) {
            if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY, "Showing home: at " + r
                    + " stackInvisible=" + stackInvisible
                    + " behindFullscreenActivity=" + behindFullscreenActivity);
            behindFullscreenActivity = true;
        }
        return behindFullscreenActivity;
    }

    private void makeVisibleIfNeeded(ActivityRecord starting, ActivityRecord r) {

        // This activity is not currently visible, but is running. Tell it to become visible.
        if (r.state == ActivityState.RESUMED || r == starting) {
            if (DEBUG_VISIBILITY) Slog.d(TAG_VISIBILITY,
                    "Not making visible, r=" + r + " state=" + r.state + " starting=" + starting);
            return;
        }

        // If this activity is paused, tell it to now show its window.
        if (DEBUG_VISIBILITY) Slog.v(TAG_VISIBILITY,
                "Making visible and scheduling visibility: " + r);
        try {
            if (mTranslucentActivityWaiting != null) {
                r.updateOptionsLocked(r.returningOptions);
                mUndrawnActivitiesBelowTopTranslucent.add(r);
            }
            setVisible(r, true);
            r.sleeping = false;
            r.app.pendingUiClean = true;
            r.app.thread.scheduleWindowVisibility(r.appToken, true);
            // The activity may be waiting for stop, but that is no longer
            // appropriate for it.
            mStackSupervisor.mStoppingActivities.remove(r);
            mStackSupervisor.mGoingToSleepActivities.remove(r);
        } catch (Exception e) {
            // Just skip on any failure; we'll make it
            // visible when it next restarts.
            Slog.w(TAG, "Exception thrown making visibile: " + r.intent.getComponent(), e);
        }
        handleAlreadyVisible(r);
    }

    private boolean handleAlreadyVisible(ActivityRecord r) {
        r.stopFreezingScreenLocked(false);
        try {
            if (r.returningOptions != null) {
                r.app.thread.scheduleOnNewActivityOptions(r.appToken, r.returningOptions);
            }
        } catch(RemoteException e) {
        }
        return r.state == ActivityState.RESUMED;
    }

    void convertActivityToTranslucent(ActivityRecord r) {
        mTranslucentActivityWaiting = r;
        mUndrawnActivitiesBelowTopTranslucent.clear();
        mHandler.sendEmptyMessageDelayed(TRANSLUCENT_TIMEOUT_MSG, TRANSLUCENT_CONVERSION_TIMEOUT);
    }

    void clearOtherAppTimeTrackers(AppTimeTracker except) {
        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final TaskRecord task = mTaskHistory.get(taskNdx);
            final ArrayList<ActivityRecord> activities = task.mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                if ( r.appTimeTracker != except) {
                    r.appTimeTracker = null;
                }
            }
        }
    }

    /**
     * Called as activities below the top translucent activity are redrawn. When the last one is
     * redrawn notify the top activity by calling
     * {@link Activity#onTranslucentConversionComplete}.
     *
     * @param r The most recent background activity to be drawn. Or, if r is null then a timeout
     * occurred and the activity will be notified immediately.
     */
    void notifyActivityDrawnLocked(ActivityRecord r) {
        mActivityContainer.setDrawn();
        if ((r == null)
                || (mUndrawnActivitiesBelowTopTranslucent.remove(r) &&
                        mUndrawnActivitiesBelowTopTranslucent.isEmpty())) {
            // The last undrawn activity below the top has just been drawn. If there is an
            // opaque activity at the top, notify it that it can become translucent safely now.
            final ActivityRecord waitingActivity = mTranslucentActivityWaiting;
            mTranslucentActivityWaiting = null;
            mUndrawnActivitiesBelowTopTranslucent.clear();
            mHandler.removeMessages(TRANSLUCENT_TIMEOUT_MSG);

            if (waitingActivity != null) {
                mWindowManager.setWindowOpaque(waitingActivity.appToken, false);
                if (waitingActivity.app != null && waitingActivity.app.thread != null) {
                    try {
                        waitingActivity.app.thread.scheduleTranslucentConversionComplete(
                                waitingActivity.appToken, r != null);
                    } catch (RemoteException e) {
                    }
                }
            }
        }
    }

    /** If any activities below the top running one are in the INITIALIZING state and they have a
     * starting window displayed then remove that starting window. It is possible that the activity
     * in this state will never resumed in which case that starting window will be orphaned. */
    void cancelInitializingActivities() {
        final ActivityRecord topActivity = topRunningActivityLocked();
        boolean aboveTop = true;
        // We don't want to clear starting window for activities that aren't behind fullscreen
        // activities as we need to display their starting window until they are done initializing.
        boolean behindFullscreenActivity = false;

        if (getStackVisibilityLocked(null) == STACK_INVISIBLE) {
            // The stack is not visible, so no activity in it should be displaying a starting
            // window. Mark all activities below top and behind fullscreen.
            aboveTop = false;
            behindFullscreenActivity = true;
        }

        for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
            final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
            for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                if (aboveTop) {
                    if (r == topActivity) {
                        aboveTop = false;
                    }
                    behindFullscreenActivity |= r.fullscreen;
                    continue;
                }

                if (r.state == ActivityState.INITIALIZING
                        && r.mStartingWindowState == STARTING_WINDOW_SHOWN
                        && behindFullscreenActivity) {
                    if (DEBUG_VISIBILITY) Slog.w(TAG_VISIBILITY,
                            "Found orphaned starting window " + r);
                    r.mStartingWindowState = STARTING_WINDOW_REMOVED;
                    mWindowManager.removeAppStartingWindow(r.appToken);
                }

                behindFullscreenActivity |= r.fullscreen;
            }
        }
    }

    /**
     * Ensure that the top activity in the stack is resumed.
     *
     * @param prev The previously resumed activity, for when in the process
     * of pausing; can be null to call from elsewhere.
     * @param options Activity options.
     *
     * @return Returns true if something is being resumed, or false if
     * nothing happened.
     *
     * NOTE: It is not safe to call this method directly as it can cause an activity in a
     *       non-focused stack to be resumed.
     *       Use {@link ActivityStackSupervisor#resumeFocusedStackTopActivityLocked} to resume the
     *       right activity for the current system state.
     */
    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        if (mStackSupervisor.inResumeTopActivity) {
            // Don't even start recursing.
            return false;
        }

        boolean result = false;
        try {
            // Protect against recursion.
            mStackSupervisor.inResumeTopActivity = true;
            if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEAVING) {
                mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN;
                mService.updateSleepIfNeededLocked();
            }
            result = resumeTopActivityInnerLocked(prev, options);
        } finally {
            mStackSupervisor.inResumeTopActivity = false;
        }
        return result;
    }

    private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
        if (DEBUG_LOCKSCREEN) mService.logLockScreen("");

        if (!mService.mBooting && !mService.mBooted) {
            // Not ready yet!
            return false;
        }

        ActivityRecord parent = mActivityContainer.mParentActivity;
        if ((parent != null && parent.state != ActivityState.RESUMED) ||
                !mActivityContainer.isAttachedLocked()) {
            // Do not resume this stack if its parent is not resumed.
            // TODO: If in a loop, make sure that parent stack resumeTopActivity is called 1st.
            return false;
        }

        mStackSupervisor.cancelInitializingActivities();

        // Find the first activity that is not finishing.
        final ActivityRecord next = topRunningActivityLocked();

        // Remember how we'll process this pause/resume situation, and ensure
        // that the state is reset however we wind up proceeding.
        final boolean userLeaving = mStackSupervisor.mUserLeaving;
        mStackSupervisor.mUserLeaving = false;

        final TaskRecord prevTask = prev != null ? prev.task : null;
        if (next == null) {
            // There are no more activities!
            final String reason = "noMoreActivities";
            final int returnTaskType = prevTask == null || !prevTask.isOverHomeStack()
                    ? HOME_ACTIVITY_TYPE : prevTask.getTaskToReturnTo();
            if (!mFullscreen && adjustFocusToNextFocusableStackLocked(returnTaskType, reason)) {
                // Try to move focus to the next visible stack with a running activity if this
                // stack is not covering the entire screen.
                return mStackSupervisor.resumeFocusedStackTopActivityLocked(
                        mStackSupervisor.getFocusedStack(), prev, null);
            }

            // Let's just start up the Launcher...
            ActivityOptions.abort(options);
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "resumeTopActivityLocked: No more activities go home");
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            // Only resume home if on home display
            return isOnHomeDisplay() &&
                    mStackSupervisor.resumeHomeStackTask(returnTaskType, prev, reason);
        }

        next.delayedResume = false;

        // If the top activity is the resumed one, nothing to do.
        if (mResumedActivity == next && next.state == ActivityState.RESUMED &&
                    mStackSupervisor.allResumedActivitiesComplete()) {
            // Make sure we have executed any pending transitions, since there
            // should be nothing left to do at this point.
            mWindowManager.executeAppTransition();
            mNoAnimActivities.clear();
            ActivityOptions.abort(options);
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "resumeTopActivityLocked: Top activity resumed " + next);
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return false;
        }

        final TaskRecord nextTask = next.task;
        if (prevTask != null && prevTask.stack == this &&
                prevTask.isOverHomeStack() && prev.finishing && prev.frontOfTask) {
            if (DEBUG_STACK)  mStackSupervisor.validateTopActivitiesLocked();
            if (prevTask == nextTask) {
                prevTask.setFrontOfTask();
            } else if (prevTask != topTask()) {
                // This task is going away but it was supposed to return to the home stack.
                // Now the task above it has to return to the home task instead.
                final int taskNdx = mTaskHistory.indexOf(prevTask) + 1;
                mTaskHistory.get(taskNdx).setTaskToReturnTo(HOME_ACTIVITY_TYPE);
            } else if (!isOnHomeDisplay()) {
                return false;
            } else if (!isHomeStack()){
                if (DEBUG_STATES) Slog.d(TAG_STATES,
                        "resumeTopActivityLocked: Launching home next");
                final int returnTaskType = prevTask == null || !prevTask.isOverHomeStack() ?
                        HOME_ACTIVITY_TYPE : prevTask.getTaskToReturnTo();
                return isOnHomeDisplay() &&
                        mStackSupervisor.resumeHomeStackTask(returnTaskType, prev, "prevFinished");
            }
        }

        // If we are sleeping, and there is no resumed activity, and the top
        // activity is paused, well that is the state we want.
        if (mService.isSleepingOrShuttingDownLocked()
                && mLastPausedActivity == next
                && mStackSupervisor.allPausedActivitiesComplete()) {
            // Make sure we have executed any pending transitions, since there
            // should be nothing left to do at this point.
            mWindowManager.executeAppTransition();
            mNoAnimActivities.clear();
            ActivityOptions.abort(options);
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "resumeTopActivityLocked: Going to sleep and all paused");
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return false;
        }

        // Make sure that the user who owns this activity is started.  If not,
        // we will just leave it as is because someone should be bringing
        // another user's activities to the top of the stack.
        if (!mService.mUserController.hasStartedUserState(next.userId)) {
            Slog.w(TAG, "Skipping resume of top activity " + next
                    + ": user " + next.userId + " is stopped");
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return false;
        }

        // The activity may be waiting for stop, but that is no longer
        // appropriate for it.
        mStackSupervisor.mStoppingActivities.remove(next);
        mStackSupervisor.mGoingToSleepActivities.remove(next);
        next.sleeping = false;
        mStackSupervisor.mWaitingVisibleActivities.remove(next);

        if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Resuming " + next);

        // If we are currently pausing an activity, then don't do anything until that is done.
        if (!mStackSupervisor.allPausedActivitiesComplete()) {
            if (DEBUG_SWITCH || DEBUG_PAUSE || DEBUG_STATES) Slog.v(TAG_PAUSE,
                    "resumeTopActivityLocked: Skip resume: some activity pausing.");
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return false;
        }

        mStackSupervisor.setLaunchSource(next.info.applicationInfo.uid);

        // We need to start pausing the current activity so the top one can be resumed...
        final boolean dontWaitForPause = (next.info.flags & FLAG_RESUME_WHILE_PAUSING) != 0;
        boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, next, dontWaitForPause);
        if (mResumedActivity != null) {
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "resumeTopActivityLocked: Pausing " + mResumedActivity);
            pausing |= startPausingLocked(userLeaving, false, next, dontWaitForPause);
        }
        if (pausing) {
            if (DEBUG_SWITCH || DEBUG_STATES) Slog.v(TAG_STATES,
                    "resumeTopActivityLocked: Skip resume: need to start pausing");
            // At this point we want to put the upcoming activity's process
            // at the top of the LRU list, since we know we will be needing it
            // very soon and it would be a waste to let it get killed if it
            // happens to be sitting towards the end.
            if (next.app != null && next.app.thread != null) {
                mService.updateLruProcessLocked(next.app, true, null);
            }
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return true;
        } else if (mResumedActivity == next && next.state == ActivityState.RESUMED &&
                mStackSupervisor.allResumedActivitiesComplete()) {
            // It is possible for the activity to be resumed when we paused back stacks above if the
            // next activity doesn't have to wait for pause to complete.
            // So, nothing else to-do except:
            // Make sure we have executed any pending transitions, since there
            // should be nothing left to do at this point.
            mWindowManager.executeAppTransition();
            mNoAnimActivities.clear();
            ActivityOptions.abort(options);
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "resumeTopActivityLocked: Top activity resumed (dontWaitForPause) " + next);
            if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
            return true;
        }

        // If the most recent activity was noHistory but was only stopped rather
        // than stopped+finished because the device went to sleep, we need to make
        // sure to finish it as we're making a new activity topmost.
        if (mService.isSleepingLocked() && mLastNoHistoryActivity != null &&
                !mLastNoHistoryActivity.finishing) {
            if (DEBUG_STATES) Slog.d(TAG_STATES,
                    "no-history finish of " + mLastNoHistoryActivity + " on new resume");
            requestFinishActivityLocked(mLastNoHistoryActivity.appToken, Activity.RESULT_CANCELED,
                    null, "resume-no-history", false);
            mLastNoHistoryActivity = null;
        }

        if (prev != null && prev != next) {
            if (!mStackSupervisor.mWaitingVisibleActivities.contains(prev)
                    && next != null && !next.nowVisible) {
                mStackSupervisor.mWaitingVisibleActivities.add(prev);
                if (DEBUG_SWITCH) Slog.v(TAG_SWITCH,
                        "Resuming top, waiting visible to hide: " + prev);
            } else {
                // The next activity is already visible, so hide the previous
                // activity's windows right now so we can show the new one ASAP.
                // We only do this if the previous is finishing, which should mean
                // it is on top of the one being resumed so hiding it quickly
                // is good.  Otherwise, we want to do the normal route of allowing
                // the resumed activity to be shown so we can decide if the
                // previous should actually be hidden depending on whether the
                // new one is found to be full-screen or not.
                if (prev.finishing) {
                    mWindowManager.setAppVisibility(prev.appToken, false);
                    if (DEBUG_SWITCH) Slog.v(TAG_SWITCH,
                            "Not waiting for visible to hide: " + prev + ", waitingVisible="
                            + mStackSupervisor.mWaitingVisibleActivities.contains(prev)
                            + ", nowVisible=" + next.nowVisible);
                } else {
                    if (DEBUG_SWITCH) Slog.v(TAG_SWITCH,
                            "Previous already visible but still waiting to hide: " + prev
                            + ", waitingVisible="
                            + mStackSupervisor.mWaitingVisibleActivities.contains(prev)
                            + ", nowVisible=" + next.nowVisible);
                }
            }
        }

        // Launching this app's activity, make sure the app is no longer
        // considered stopped.
        try {
            AppGlobals.getPackageManager().setPackageStoppedState(
                    next.packageName, false, next.userId); /* TODO: Verify if correct userid */
        } catch (RemoteException e1) {
        } catch (IllegalArgumentException e) {
            Slog.w(TAG, "Failed trying to unstop package "
                    + next.packageName + ": " + e);
        }

        // We are starting up the next activity, so tell the window manager
        // that the previous one will be hidden soon.  This way it can know
        // to ignore it when computing the desired screen orientation.
        boolean anim = true;
        if (prev != null) {
            if (prev.finishing) {
                if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION,
                        "Prepare close transition: prev=" + prev);
                if (mNoAnimActivities.contains(prev)) {
                    anim = false;
                    mWindowManager.prepareAppTransition(TRANSIT_NONE, false);
                } else {
                    mWindowManager.prepareAppTransition(prev.task == next.task
                            ? TRANSIT_ACTIVITY_CLOSE
                            : TRANSIT_TASK_CLOSE, false);
                }
                mWindowManager.setAppVisibility(prev.appToken, false);
            } else {
                if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION,
                        "Prepare open transition: prev=" + prev);
                if (mNoAnimActivities.contains(next)) {
                    anim = false;
                    mWindowManager.prepareAppTransition(TRANSIT_NONE, false);
                } else {
                    mWindowManager.prepareAppTransition(prev.task == next.task
                            ? TRANSIT_ACTIVITY_OPEN
                            : next.mLaunchTaskBehind
                                    ? TRANSIT_TASK_OPEN_BEHIND
                                    : TRANSIT_TASK_OPEN, false);
                }
            }
        } else {
            if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION, "Prepare open transition: no previous");
            if (mNoAnimActivities.contains(next)) {
                anim = false;
                mWindowManager.prepareAppTransition(TRANSIT_NONE, false);
            } else {
                mWindowManager.prepareAppTransition(TRANSIT_ACTIVITY_OPEN, false);
            }
        }

        Bundle resumeAnimOptions = null;
        if (anim) {
            ActivityOptions opts = next.getOptionsForTargetActivityLocked();
            if (opts != null) {
                resumeAnimOptions = opts.toBundle();
            }
            next.applyOptionsLocked();
        } else {
            next.clearOptionsLocked();
        }

        ActivityStack lastStack = mStackSupervisor.getLastStack();
        if (next.app != null && next.app.thread != null) {
            if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Resume running: " + next
                    + " stopped=" + next.stopped + " visible=" + next.visible);

            // If the previous activity is translucent, force a visibility update of
            // the next activity, so that it's added to WM's opening app list, and
            // transition animation can be set up properly.
            // For example, pressing Home button with a translucent activity in focus.
            // Launcher is already visible in this case. If we don't add it to opening
            // apps, maybeUpdateTransitToWallpaper() will fail to identify this as a
            // TRANSIT_WALLPAPER_OPEN animation, and run some funny animation.
            final boolean lastActivityTranslucent = lastStack != null
                    && (!lastStack.mFullscreen
                    || (lastStack.mLastPausedActivity != null
                    && !lastStack.mLastPausedActivity.fullscreen));

            // This activity is now becoming visible.
            if (!next.visible || next.stopped || lastActivityTranslucent) {
                mWindowManager.setAppVisibility(next.appToken, true);
            }

            // schedule launch ticks to collect information about slow apps.
            next.startLaunchTickingLocked();

            ActivityRecord lastResumedActivity =
                    lastStack == null ? null :lastStack.mResumedActivity;
            ActivityState lastState = next.state;

            mService.updateCpuStats();

            if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to RESUMED: " + next + " (in existing)");
            next.state = ActivityState.RESUMED;
            mResumedActivity = next;
            next.task.touchActiveTime();
            mRecentTasks.addLocked(next.task);
            mService.updateLruProcessLocked(next.app, true, null);
            updateLRUListLocked(next);
            mService.updateOomAdjLocked();

            // Have the window manager re-evaluate the orientation of
            // the screen based on the new activity order.
            boolean notUpdated = true;
            if (mStackSupervisor.isFocusedStack(this)) {
                Configuration config = mWindowManager.updateOrientationFromAppTokens(
                        mService.mConfiguration,
                        next.mayFreezeScreenLocked(next.app) ? next.appToken : null);
                if (config != null) {
                    next.frozenBeforeDestroy = true;
                }
                notUpdated = !mService.updateConfigurationLocked(config, next, false);
            }

            if (notUpdated) {
                // The configuration update wasn't able to keep the existing
                // instance of the activity, and instead started a new one.
                // We should be all done, but let's just make sure our activity
                // is still at the top and schedule another run if something
                // weird happened.
                ActivityRecord nextNext = topRunningActivityLocked();
                if (DEBUG_SWITCH || DEBUG_STATES) Slog.i(TAG_STATES,
                        "Activity config changed during resume: " + next
                        + ", new next: " + nextNext);
                if (nextNext != next) {
                    // Do over!
                    mStackSupervisor.scheduleResumeTopActivities();
                }
                if (mStackSupervisor.reportResumedActivityLocked(next)) {
                    mNoAnimActivities.clear();
                    if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
                    return true;
                }
                if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
                return false;
            }

            try {
                // Deliver all pending results.
                ArrayList<ResultInfo> a = next.results;
                if (a != null) {
                    final int N = a.size();
                    if (!next.finishing && N > 0) {
                        if (DEBUG_RESULTS) Slog.v(TAG_RESULTS,
                                "Delivering results to " + next + ": " + a);
                        next.app.thread.scheduleSendResult(next.appToken, a);
                    }
                }

                boolean allowSavedSurface = true;
                if (next.newIntents != null) {
                    // Restrict saved surface to launcher start, or there is no intent at all
                    // (eg. task being brought to front). If the intent is something else,
                    // likely the app is going to show some specific page or view, instead of
                    // what's left last time.
                    for (int i = next.newIntents.size() - 1; i >= 0; i--) {
                        final Intent intent = next.newIntents.get(i);
                        if (intent != null && !ActivityRecord.isMainIntent(intent)) {
                            allowSavedSurface = false;
                            break;
                        }
                    }
                    next.app.thread.scheduleNewIntent(
                            next.newIntents, next.appToken, false /* andPause */);
                }

                // Well the app will no longer be stopped.
                // Clear app token stopped state in window manager if needed.
                mWindowManager.notifyAppResumed(next.appToken, next.stopped, allowSavedSurface);

                EventLog.writeEvent(EventLogTags.AM_RESUME_ACTIVITY, next.userId,
                        System.identityHashCode(next), next.task.taskId, next.shortComponentName);

                next.sleeping = false;
                mService.showUnsupportedZoomDialogIfNeededLocked(next);
                mService.showAskCompatModeDialogLocked(next);
                next.app.pendingUiClean = true;
                next.app.forceProcessStateUpTo(mService.mTopProcessState);
                next.clearOptionsLocked();
                next.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,
                        mService.isNextTransitionForward(), resumeAnimOptions);

                mStackSupervisor.checkReadyForSleepLocked();

                if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Resumed " + next);
            } catch (Exception e) {
                // Whoops, need to restart this activity!
                if (DEBUG_STATES) Slog.v(TAG_STATES, "Resume failed; resetting state to "
                        + lastState + ": " + next);
                next.state = lastState;
                if (lastStack != null) {
                    lastStack.mResumedActivity = lastResumedActivity;
                }
                Slog.i(TAG, "Restarting because process died: " + next);
                if (!next.hasBeenLaunched) {
                    next.hasBeenLaunched = true;
                } else  if (SHOW_APP_STARTING_PREVIEW && lastStack != null &&
                        mStackSupervisor.isFrontStack(lastStack)) {
                    next.showStartingWindow(null, true);
                }
                mStackSupervisor.startSpecificActivityLocked(next, true, false);
                if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
                return true;
            }

            // From this point on, if something goes wrong there is no way
            // to recover the activity.
            try {
                completeResumeLocked(next);
            } catch (Exception e) {
                // If any exception gets thrown, toss away this
                // activity and try the next one.
                Slog.w(TAG, "Exception thrown during resume of " + next, e);
                requestFinishActivityLocked(next.appToken, Activity.RESULT_CANCELED, null,
                        "resume-exception", true);
                if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
                return true;
            }
        } else {
            // Whoops, need to restart this activity!
            if (!next.hasBeenLaunched) {
                next.hasBeenLaunched = true;
            } else {
                if (SHOW_APP_STARTING_PREVIEW) {
                    next.showStartingWindow(null, true);
                }
                if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);
            }
            if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next);
            mStackSupervisor.startSpecificActivityLocked(next, true, true);
        }

        if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
        return true;
    }

    private TaskRecord getNextTask(TaskRecord targetTask) {
        final int index = mTaskHistory.indexOf(targetTask);
        if (index >= 0) {
            final int numTasks = mTaskHistory.size();
            for (int i = index + 1; i < numTasks; ++i) {
                TaskRecord task = mTaskHistory.get(i);
                if (task.userId == targetTask.userId) {
                    return task;
                }
            }
        }
        return null;
    }

    private void insertTaskAtPosition(TaskRecord task, int position) {
        if (position >= mTaskHistory.size()) {
            insertTaskAtTop(task, null);
            return;
        }
        // Calculate maximum possible position for this task.
        int maxPosition = mTaskHistory.size();
        if (!mStackSupervisor.isCurrentProfileLocked(task.userId)
                && task.topRunningActivityLocked() == null) {
            // Put non-current user tasks below current user tasks.
            while (maxPosition > 0) {
                final TaskRecord tmpTask = mTaskHistory.get(maxPosition - 1);
                if (!mStackSupervisor.isCurrentProfileLocked(tmpTask.userId)
                        || tmpTask.topRunningActivityLocked() == null) {
                    break;
                }
                maxPosition--;
            }
        }
        position = Math.min(position, maxPosition);
        mTaskHistory.remove(task);
        mTaskHistory.add(position, task);
        updateTaskMovement(task, true);
    }

    private void insertTaskAtTop(TaskRecord task, ActivityRecord newActivity) {
        boolean isLastTaskOverHome = false;
        // If the moving task is over home stack, transfer its return type to next task
        if (task.isOverHomeStack()) {
            final TaskRecord nextTask = getNextTask(task);
            if (nextTask != null) {
                nextTask.setTaskToReturnTo(task.getTaskToReturnTo());
            } else {
                isLastTaskOverHome = true;
            }
        }

        // If this is being moved to the top by another activity or being launched from the home
        // activity, set mTaskToReturnTo accordingly.
        if (isOnHomeDisplay()) {
            ActivityStack lastStack = mStackSupervisor.getLastStack();
            final boolean fromHome = lastStack.isHomeStack();
            if (!isHomeStack() && (fromHome || topTask() != task)) {
                // If it's a last task over home - we default to keep its return to type not to
                // make underlying task focused when this one will be finished.
                int returnToType = isLastTaskOverHome
                        ? task.getTaskToReturnTo() : APPLICATION_ACTIVITY_TYPE;
                if (fromHome && StackId.allowTopTaskToReturnHome(mStackId)) {
                    returnToType = lastStack.topTask() == null
                            ? HOME_ACTIVITY_TYPE : lastStack.topTask().taskType;
                }
                task.setTaskToReturnTo(returnToType);
            }
        } else {
            task.setTaskToReturnTo(APPLICATION_ACTIVITY_TYPE);
        }

        mTaskHistory.remove(task);
        // Now put task at top.
        int taskNdx = mTaskHistory.size();
        final boolean notShownWhenLocked =
                (newActivity != null && (newActivity.info.flags & FLAG_SHOW_FOR_ALL_USERS) == 0)
                || (newActivity == null && task.topRunningActivityLocked() == null);
        if (!mStackSupervisor.isCurrentProfileLocked(task.userId) && notShownWhenLocked) {
            // Put non-current user tasks below current user tasks.
            while (--taskNdx >= 0) {
                final TaskRecord tmpTask = mTaskHistory.get(taskNdx);
                if (!mStackSupervisor.isCurrentProfileLocked(tmpTask.userId)
                        || tmpTask.topRunningActivityLocked() == null) {
                    break;
                }
            }
            ++taskNdx;
        }
        mTaskHistory.add(taskNdx, task);
        updateTaskMovement(task, true);
    }

    final void startActivityLocked(ActivityRecord r, boolean newTask, boolean keepCurTransition,
            ActivityOptions options) {
        TaskRecord rTask = r.task;
        final int taskId = rTask.taskId;
        // mLaunchTaskBehind tasks get placed at the back of the task stack.
        if (!r.mLaunchTaskBehind && (taskForIdLocked(taskId) == null || newTask)) {
            // Last activity in task had been removed or ActivityManagerService is reusing task.
            // Insert or replace.
            // Might not even be in.
            insertTaskAtTop(rTask, r);
            mWindowManager.moveTaskToTop(taskId);
        }
        TaskRecord task = null;
        if (!newTask) {
            // If starting in an existing task, find where that is...
            boolean startIt = true;
            for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
                task = mTaskHistory.get(taskNdx);
                if (task.getTopActivity() == null) {
                    // All activities in task are finishing.
                    continue;
                }
                if (task == r.task) {
                    // Here it is!  Now, if this is not yet visible to the
                    // user, then just add it without starting; it will
                    // get started when the user navigates back to it.
                    if (!startIt) {
                        if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to task "
                                + task, new RuntimeException("here").fillInStackTrace());
                        task.addActivityToTop(r);
                        r.putInHistory();
                        addConfigOverride(r, task);
                        if (VALIDATE_TOKENS) {
                            validateAppTokensLocked();
                        }
                        ActivityOptions.abort(options);
                        return;
                    }
                    break;
                } else if (task.numFullscreen > 0) {
                    startIt = false;
                }
            }
        }

        // Place a new activity at top of stack, so it is next to interact
        // with the user.

        // If we are not placing the new activity frontmost, we do not want
        // to deliver the onUserLeaving callback to the actual frontmost
        // activity
        if (task == r.task && mTaskHistory.indexOf(task) != (mTaskHistory.size() - 1)) {
            mStackSupervisor.mUserLeaving = false;
            if (DEBUG_USER_LEAVING) Slog.v(TAG_USER_LEAVING,
                    "startActivity() behind front, mUserLeaving=false");
        }

        task = r.task;

        // Slot the activity into the history stack and proceed
        if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to stack to task " + task,
                new RuntimeException("here").fillInStackTrace());
        task.addActivityToTop(r);
        task.setFrontOfTask();

        r.putInHistory();
        if (!isHomeStack() || numActivities() > 0) {
            // We want to show the starting preview window if we are
            // switching to a new task, or the next activity's process is
            // not currently running.
            boolean showStartingIcon = newTask;
            ProcessRecord proc = r.app;
            if (proc == null) {
                proc = mService.mProcessNames.get(r.processName, r.info.applicationInfo.uid);
            }
            if (proc == null || proc.thread == null) {
                showStartingIcon = true;
            }
            if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION,
                    "Prepare open transition: starting " + r);
            if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0) {
                mWindowManager.prepareAppTransition(TRANSIT_NONE, keepCurTransition);
                mNoAnimActivities.add(r);
            } else {
                mWindowManager.prepareAppTransition(newTask
                        ? r.mLaunchTaskBehind
                                ? TRANSIT_TASK_OPEN_BEHIND
                                : TRANSIT_TASK_OPEN
                        : TRANSIT_ACTIVITY_OPEN, keepCurTransition);
                mNoAnimActivities.remove(r);
            }
            addConfigOverride(r, task);
            boolean doShow = true;
            if (newTask) {
                // Even though this activity is starting fresh, we still need
                // to reset it to make sure we apply affinities to move any
                // existing activities from other tasks in to it.
                // If the caller has requested that the target task be
                // reset, then do so.
                if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
                    resetTaskIfNeededLocked(r, r);
                    doShow = topRunningNonDelayedActivityLocked(null) == r;
                }
            } else if (options != null && options.getAnimationType()
                    == ActivityOptions.ANIM_SCENE_TRANSITION) {
                doShow = false;
            }
            if (r.mLaunchTaskBehind) {
                // Don't do a starting window for mLaunchTaskBehind. More importantly make sure we
                // tell WindowManager that r is visible even though it is at the back of the stack.
                mWindowManager.setAppVisibility(r.appToken, true);
                ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
            } else if (SHOW_APP_STARTING_PREVIEW && doShow) {
                // Figure out if we are transitioning from another activity that is
                // "has the same starting icon" as the next one.  This allows the
                // window manager to keep the previous window it had previously
                // created, if it still had one.
                ActivityRecord prev = r.task.topRunningActivityWithStartingWindowLocked();
                if (prev != null) {
                    // We don't want to reuse the previous starting preview if:
                    // (1) The current activity is in a different task.
                    if (prev.task != r.task) {
                        prev = null;
                    }
                    // (2) The current activity is already displayed.
                    else if (prev.nowVisible) {
                        prev = null;
                    }
                }
                r.showStartingWindow(prev, showStartingIcon);
            }
        } else {
            // If this is the first activity, don't do any fancy animations,
            // because there is nothing for it to animate on top of.
            addConfigOverride(r, task);
            ActivityOptions.abort(options);
            options = null;
        }
        if (VALIDATE_TOKENS) {
            validateAppTokensLocked();
        }
    }

    final void validateAppTokensLocked() {
        mValidateAppTokens.clear();
        mValidateAppTokens.ensureCapacity(numActivities());
        final int numTasks = mTaskHistory.size();
        for (int taskNdx = 0; taskNdx < numTasks; ++taskNdx) {
            TaskRecord task = mTaskHistory.get(taskNdx);
            final ArrayList<ActivityRecord> activities = task.mActivities;
            if (activities.isEmpty()) {
                continue;
            }
            TaskGroup group = new TaskGroup();
            group.taskId = task.taskId;
            mValidateAppTokens.add(group);
            final int numActivities = activities.size();
            for (int activityNdx = 0; activityNdx < numActivities; ++activityNdx) {
                final ActivityRecord r = activities.get(activityNdx);
                group.tokens.add(r.appToken);
            }
        }
        mWindowManager.validateAppTokens(mStackId, mValidateAppTokens);
    }

    /**
     * Perform a reset of the given task, if needed as part of launching it.
     * Returns the new HistoryRecord at the top of the task.
     */
    /**
     * Helper method for #resetTaskIfNeededLocked.
     * We are inside of the task being reset...  we'll either finish this activity, push it out
     * for another task, or leave it as-is.
     * @param task The task containing the Activity (taskTop) that might be reset.
     * @param forceReset
     * @return An ActivityOptions that needs to be processed.
     */
    final ActivityOptions resetTargetTaskIfNeededLocked(TaskRecord task, boolean forceReset) {
        ActivityOptions topOptions = null;

        int replyChainEnd = -1;
        boolean canMoveOptions = true;

        // We only do this for activities that are not the root of the task (since if we finish
        // the root, we may no longer have the task!).
        final ArrayList<ActivityRecord> activities = task.mActivities;
        final int numActivities = activities.size();
        final int rootActivityNdx = task.findEffectiveRootIndex();
        for (int i = numActivities - 1; i > rootActivityNdx; --i ) {
            ActivityRecord target = activities.get(i);
            if (target.frontOfTask)
                break;

            final int flags = target.info.flags;
            final boolean finishOnTaskLaunch =
                    (flags & ActivityInfo.FLAG_FINISH_ON_TASK_LAUNCH) != 0;
            final boolean allowTaskReparenting =
                    (flags & ActivityInfo.FLAG_ALLOW_TASK_REPARENTING) != 0;
            final boolean clearWhenTaskReset =
                    (target.intent.getFlags() & Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET) != 0;

            if (!finishOnTaskLaunch
                    && !clearWhenTaskReset
                    && target.resultTo != null) {
                // If this activity is sending a reply to a previous
                // activity, we can't do anything with it now until
                // we reach the start of the reply chain.
                // XXX note that we are assuming the result is always
                // to the previous activity, which is almost always
                // the case but we really shouldn't count on.
                if (replyChainEnd < 0) {
                    replyChainEnd = i;
                }
            } else if (!finishOnTaskLaunch
                    && !clearWhenTaskReset
                    && allowTaskReparenting
                    && target.taskAffinity != null
                    && !target.taskAffinity.equals(task.affinity)) {
                // If this activity has an affinity for another
                // task, then we need to move it out of here.  We will
                // move it as far out of the way as possible, to the
                // bottom of the activity stack.  This also keeps it
                // correctly ordered with any activities we previously
                // moved.
                final TaskRecord targetTask;
                final ActivityRecord bottom =
                        !mTaskHistory.isEmpty() && !mTaskHistory.get(0).mActivities.isEmpty() ?
                                mTaskHistory.get(0).mActivities.get(0) : null;
                if (bottom != null && target.taskAffinity != null
                        && target.taskAffinity.equals(bottom.task.affinity)) {
                    // If the activity currently at the bottom has the
                    // same task affinity as the one we are moving,
                    // then merge it into the same task.