一. 前言

        接上一篇文章 AMS组成 , 介绍了一下AMS的内部数据结构,  ProcessRecord容器,还有四大组件记录表 ,  本篇文章继续讲解一下与Activity管理相关的数据结构,  重点关注如下4个类文件:ActivityRecord   TaskRecord    ActivityStack  ActivityStackSupervisor

基本概念:

• ActivityRecord: 记录着Activity信息
• TaskRecord: 记录着task信息
• ActivityStack: 栈信息
• ActivityStackSupervisor : 栈管理者

二. ActivityRecord

        ActivityRecord，源码中的注释介绍：An entry in the history stack, representing an activity.翻译：历史栈中的一个条目，代表一个activity.

final class ActivityRecord extends ConfigurationContainer {
....
    final ActivityTaskManagerService mAtmService; // owner
    final IApplicationToken.Stub appToken; // window manager token
    
     final ActivityInfo info; // all about me
    // TODO: This is duplicated state already contained in info.applicationInfo - remove
    ApplicationInfo appInfo; // information about activity's app

    //ActivityRecord所在的TaskRecord
    TaskRecord task;        // the task this is in.

    //ActivityRecord的构造方法, 需要传递大量的信息
    ActivityRecord(ActivityTaskManagerService _service, WindowProcessController _caller,
            int _launchedFromPid, int _launchedFromUid, String _launchedFromPackage, Intent _intent,
            String _resolvedType, ActivityInfo aInfo, Configuration _configuration,
            ActivityRecord _resultTo, String _resultWho, int _reqCode, boolean _componentSpecified,
            boolean _rootVoiceInteraction, ActivityStackSupervisor supervisor,
            ActivityOptions options, ActivityRecord sourceRecord) {
        mAtmService = _service;
        mRootActivityContainer = _service.mRootActivityContainer;
        appToken = new Token(this, _intent);
        info = aInfo;
        launchedFromPid = _launchedFromPid;
        launchedFromUid = _launchedFromUid;
        launchedFromPackage = _launchedFromPackage;
        mUserId = UserHandle.getUserId(aInfo.applicationInfo.uid);
        intent = _intent;
        shortComponentName = _intent.getComponent().flattenToShortString();
        resolvedType = _resolvedType;
        componentSpecified = _componentSpecified;
        rootVoiceInteraction = _rootVoiceInteraction;
        mLastReportedConfiguration = new MergedConfiguration(_configuration);
        resultTo = _resultTo;
        resultWho = _resultWho;
        requestCode = _reqCode;
        //省略剩下的参数

....
}

ActivityRecord中存在着大量的成员变量，包含了一个Activity的所有信息。
ActivityRecord中的成员变量task表示其所在的TaskRecord，由此可以看出：ActivityRecord与TaskRecord建立了联系.

列举出重要的成员变量

序号	成员变量	描述
1	ProcessRecord app	运行在哪个进程
2	TaskRecord task	运行在哪个task
3	ActivityInfo info	Activity的信息
4	int mActivityType	Activity类型
5	ActivityState state	Activity的状态
6	ApplicationInfo appInfo	运行在哪个app中
7	ComponentName realActivity	组件名
8	String packageName	包名
9	String processName	进程名
10	int launchMode	启动模式
11	int userId	该Activity运行在哪个用户id

Activity类型

    /** Activity type is currently not defined.  未定义类型*/
    public static final int ACTIVITY_TYPE_UNDEFINED = 0;

    /**标准Activity类型 Standard activity type. Nothing special about the activity... */
    public static final int ACTIVITY_TYPE_STANDARD = 1;

    /** 桌面类型 Home/Launcher activity type. */
    public static final int ACTIVITY_TYPE_HOME = 2;

    /** 最近任务类型  Recents/Overview activity type. There is only one activity with this type in the system. */
    public static final int ACTIVITY_TYPE_RECENTS = 3;

    /** 辅助Activity类型Assistant activity type. */
    public static final int ACTIVITY_TYPE_ASSISTANT = 4;

Activity的状态ActivityState 

enum ActivityState {
        INITIALIZING,
        RESUMED,     //已恢复
        PAUSING,
        PAUSED,      //已暂停
        STOPPING, 
        STOPPED,     //已停止
        FINISHING,
        DESTROYING,
        DESTROYED,   //已销毁
        RESTARTING_PROCESS
    }

时间相关的成员变量：

时间点	赋值时间	含义
createTime	new ActivityRecord	Activity首次创建时间点
displayStartTime	AS.setLaunchTime	Activity首次启动时间点
fullyDrawnStartTime	AS.setLaunchTime	Activity首次启动时间点
startTime		Activity上次启动的时间点
lastVisibleTime	AR.windowsVisibleLocked	Activity上次成为可见的时间点
cpuTimeAtResume	AS.completeResumeLocked	从Rsume以来的cpu使用时长
pauseTime	AS.startPausingLocked	Activity上次暂停的时间点
launchTickTime	AR.startLaunchTickingLocked	Eng版本才赋值
lastLaunchTime	ASS.realStartActivityLocked	上一次启动时间

其中AR是指ActivityRecord, AS是指ActivityStack。

三. TaskRecord

         Task的信息记录在TaskRecord对象.

         TaskRecord，内部维护一个 ArrayList<ActivityRecord> 用来保存ActivityRecord。
frameworks/base/services/core/java/com/android/server/am/TaskRecord.java

 final int taskId;       // Unique identifier for this task. 任务ID
 /** List of all activities in the task arranged in history order */
 //使用一个ArrayList来保存所有的ActivityRecord
 final ArrayList<ActivityRecord> mActivities;
 //TaskRecord所在的ActivityStack
 private ActivityStack mStack; 



//构造方法
TaskRecord(ActivityTaskManagerService service, int _taskId, ActivityInfo info, Intent _intent,
            IVoiceInteractionSession _voiceSession, IVoiceInteractor _voiceInteractor) {
        mService = service;
        userId = UserHandle.getUserId(info.applicationInfo.uid);
        taskId = _taskId;
        lastActiveTime = SystemClock.elapsedRealtime();
        mAffiliatedTaskId = _taskId;
        voiceSession = _voiceSession;
        voiceInteractor = _voiceInteractor;
        isAvailable = true;
        mActivities = new ArrayList<>();
        mCallingUid = info.applicationInfo.uid;
        mCallingPackage = info.packageName;
        setIntent(_intent, info);
        setMinDimensions(info);
        touchActiveTime();
        mService.getTaskChangeNotificationController().notifyTaskCreated(_taskId, realActivity);
    }

列出重要的成员变量信息

序号	成员变量	描述
1	ActivityStack stack	当前所属的stack
2	ArrayList mActivities	当前task的所有Activity列表
3	int taskId	taskID
4	String affinity	是指root activity的affinity，即该Task中第一个Activity;
5	int mCallingUid	调用者的UID
6	String mCallingPackage	调用者的包名

四. ActivityStack

ActivityStack,内部维护了一个 ArrayList<TaskRecord> ，用来管理TaskRecord
 

class ActivityStack extends ConfigurationContainer {
.....
   /**
     * The back history of all previous (and possibly still
     * running) activities.  It contains #TaskRecord objects.
     */
    // 使用一个ArrayList来保存TaskRecord
    private final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>();
    //持有一个 ActivityStackSupervisor，所有的运行中的ActivityStacks都通过它来进行管
    protected final ActivityStackSupervisor mStackSupervisor;

    
    //构造方法
    TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            boolean toTop, ActivityRecord activity, ActivityRecord source,
            ActivityOptions options) {
        //创建一个task
        final TaskRecord task = TaskRecord.create(
                mService, taskId, info, intent, voiceSession, voiceInteractor);
        // add the task to stack first, mTaskPositioner might need the stack association
        //将task添加到ActivityStack中去
        addTask(task, toTop, "createTaskRecord");
        final int displayId = mDisplayId != INVALID_DISPLAY ? mDisplayId : DEFAULT_DISPLAY;
        final boolean isLockscreenShown = mService.mStackSupervisor.getKeyguardController()
                .isKeyguardOrAodShowing(displayId);
        if (!mStackSupervisor.getLaunchParamsController()
                .layoutTask(task, info.windowLayout, activity, source, options)
                && !matchParentBounds() && task.isResizeable() && !isLockscreenShown) {
            task.updateOverrideConfiguration(getRequestedOverrideBounds());
        }
        task.createTask(toTop, (info.flags & FLAG_SHOW_FOR_ALL_USERS) != 0);
        return task;
    }

    //添加Task到指定位置
    void addTask(final TaskRecord task, int position, boolean schedulePictureInPictureModeChange,
            String reason) {
        // TODO: Is this remove really needed? Need to look into the call path for the other addTask
        //若存在，先移除
        mTaskHistory.remove(task);
        if (isSingleTaskInstance() && !mTaskHistory.isEmpty()) {
            throw new IllegalStateException("Can only have one child on stack=" + this);
        }

        position = getAdjustedPositionForTask(task, position, null /* starting */);
        final boolean toTop = position >= mTaskHistory.size();
        final ActivityStack prevStack = preAddTask(task, reason, toTop);
        //添加task到mTaskHistory
        mTaskHistory.add(position, task);
        //为TaskRecord设置ActivityStack
        task.setStack(this);

        updateTaskMovement(task, toTop);

        postAddTask(task, prevStack, schedulePictureInPictureModeChange);
    }
....
}

可以看到ActivityStack使用了一个ArrayList来保存TaskRecord。
另外，ActivityStack中还持有ActivityStackSupervisor对象，这个是用来管理ActivityStacks的。
ActivityStack是由ActivityStackSupervisor来创建的，实际ActivityStackSupervisor就是用来管理
ActivityStack的.

列出重要的成员变量信息

序号	成员变量	描述
1	ArrayList mTaskHistory	保存所有的Task列表
2	ArrayList mStacks	所有stack列表
3	int mStackId	栈ID
4	int mDisplayId	affinity附加的显示器的唯一标识符，如果已分离，则为-1
5	ActivityRecord mPausingActivity	正在pause状态的ActivityRecord
6	ActivityRecord mLastPausedActivity	最后pause状态ActivityRecord
7	ActivityRecord mResumedActivity	已经resumed Activity的ActivityRecord对象

所有前台stack的mResumedActivity的state == RESUMED, 则表示allResumedActivitiesComplete, 此时mLastFocusedStack = mFocusedStack;

五. ActivityStackSupervisor

ActivityStackSupervisor，顾名思义，就是用来管理ActivityStack的
frameworks/base/services/core/java/com/android/server/wm/ActivityDisplay.java

class ActivityDisplay extends ConfigurationContainer<ActivityStack>
        implements WindowContainerListener {
....
    //管理的是Launcher相关的任务
    private ActivityStack mHomeStack = null; 
    //管理的是Recent相关的任务栈
    private ActivityStack mRecentsStack = null;
    //画中画的任务栈
    private ActivityStack mPinnedStack = null;
    //分屏模式下的主屏幕栈
    private ActivityStack mSplitScreenPrimaryStack = null;
....
}

六. Activity栈关系

Activity栈结构体的组成关系:  点击查看大图

• 一般地，对于没有分屏功能以及虚拟屏的情况下，ActivityStackSupervisor与ActivityDisplay都是系统唯一；
• ActivityDisplay主要有Home Stack和App Stack这两个栈；
• 每个ActivityStack中可以有若干个TaskRecord对象；
• 每个TaskRecord包含如果个ActivityRecord对象；
• 每个ActivityRecord记录一个Activity信息。

(1)正向关系链表：

1. ActivityStackSupervisor.mActivityDisplays

2. -> ActivityDisplay.mStacks

3. -> ActivityStack.mTaskHistory

4. -> TaskRecord.mActivities

5. -> ActivityRecord

(2)反向关系链表：

1. ActivityRecord.task

2. -> TaskRecord.stack

3. -> ActivityStack.mStackSupervisor

4. -> ActivityStackSupervisor

注：ActivityStack.mDisplayId可找到所对应的ActivityDisplay；

七. 参考文章

 四大组件之ActivityRecord

AMS：ActivityRecord 理解