ActivityManagerService數據結構Activity棧管理(二)

ActivityManagerService要管理四大組件，那四大組件就必須在AMS中有存在的形式，這里先從AMS 如何管理Activity 談起；
Activity在AMS 中存在的形式為ActivityRecord；
AMS以Task的方式管理Activity，Task在AMS存在的形式為TaskRecord；TaskRecord中的mActivities用棧的方式管理ActivityRecord；
TaskRecord在AMS中依靠ActivityStack去管理，從命名來看，ActivityStack更像Activity棧，但是ActivityStack並不是Activity 棧，而是負責管理TaskRecord的類，android系統中有三種ActivityStack（mHomeStack，mFocusedStack，mLastFocusedStack）；
ActivityStack同樣有管理者，ActivityStackSupervisor負責管理ActivityStack；
每一個Activity和TaskRecord 都是屬於某個進程，所以進程還需要在AMS有存在形式， 進程在AMS中存在的形式就是ProcessRecord；

他們的關系應該是這樣的：

 

 

一、主要涉及4個類

1) ActivityRecord
源碼注釋：An entry in the history stack, representing an activity.
翻譯一下：存在歷史棧的一個實例，代表一個Activity。
2) TaskRecord
Activity棧，內部維護一個ArrayList<ActivityRecord>
3) ActivityStack
並不是一個Activity棧，真正意義上的Activity棧是TaskRecord，這個類是負責管理各個Activity棧，內部維護一個ArrayList<TaskRecord>
4) ActivityStackSupervisor
內部持有一個ActivityStack，而ActivityStack內部也持有ActivityStackSupervisor，相當於ActivityStack的輔助管理類

ActivityRecord

ActivityRecord是Activity在AMS中的存在形式，ActivityRecord保存了Activity的信息。

final class ActivityRecord {
    TaskRecord task;  // the task this is in.
    final IApplicationToken.Stub appToken;
    final int userId;
    int theme;
    int launchMode;
    ...
}

成員變量task表示自己所在的TaskRecord，這樣要找到自己所在的TaskRecord就不必遍歷查找了。

TaskRecord

我們都知道AMS以Task的方式在管理Activity，TaskRecord中的mActivities是一個棧，它的作用是以棧的方式組織管理Activity。Android把用戶一次操作相關的Activity按照先后順序保存在一個Task中，這個Task在AMS中的存在形式就是TaskRecord；

final class TaskRecord {
  ...........
  final int taskId;       // Unique identifier for this task.
  int mAffiliatedTaskId; // taskId of parent affiliation or self if no parent.
  // 是指root activity的affinity，即該Task中第一個Activity; 可以理解為當前task的name；
  String affinity;        // The affinity name for this task, or null; may change identity.
  // 啟動這個task的intent
  Intent intent;          // The original intent that started the task.
  long firstActiveTime;   // First time this task was active.
  long lastActiveTime;    // Last time this task was active, including sleep.
  boolean inRecents;      // Actually in the recents list?
  boolean isAvailable;    // Is the activity available to be launched?
  // task模式
  int mLockTaskMode;      // Which tasklock mode to launch this task in. One of
                           // ActivityManager.LOCK_TASK_LAUNCH_MODE_*

  /** List of all activities in the task arranged in history order */
  // 該Task中所有的Activity
  final ArrayList<ActivityRecord> mActivities;

  /** Current stack */
  // 管理該Task的ActivityStack
  ActivityStack stack;

  // 最近列表中,可以看到當前Task的縮略圖
  private Bitmap mLastThumbnail; // Last thumbnail captured for this item.
  private final File mLastThumbnailFile; // File containing last thumbnail.

  final ActivityManagerService mService;
  ..........
}

TaskRecord 的affinity只有在其被創建的時候才有用，以后加入這個Task的Activity，即使他們通過taskAffinity指定了一個不同的字符串，也不會更改Task的名稱；Activity所在的Task通過AndroidManifest.xml中<Activity>標簽中的android:taskAffinity="xxx"來指定，通常不去主動設置一個Activity的taskAffinity屬性，那么taskAffinity的值缺省使用包名。正因為如此，應用中所有的Activity的taskAffinity屬性值默認都是相同的，都是包名，所以在應用中使用FLAG_ACTIVITY_NEW_TASK標志去啟動一個本應用中的一個Activity，也不會創建一個新的task，除非這個Activity 額外指定了不同的taskAffinity屬性值；

ActivityStack

ActivityStack充當TaskRecord的Manager角色；

final class ActivityStack {
   private final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>(); //ActivityStack中所有的TaskRecord
    private final ArrayList<ActivityRecord> mLRUActivities = new ArrayList<>();//最近活動過的ActivityRecord
    ......  
    final int mStackId;  //ActivityStack的唯一標識
    final ActivityContainer mActivityContainer;
    /** The other stacks, in order, on the attached display. Updated at attach/detach time. */
    ArrayList<ActivityStack> mStacks; //綁定的ActivityDisplay中的所有ActivityStack
    /** The attached Display's unique identifier, or -1 if detached */
    int mDisplayId;//綁定的ActivityDisplay的id，默認為Display.DEFAULT_DISPLAY = 0；
    ......  
    /** Run all ActivityStacks through this */  
    final ActivityStackSupervisor mStackSupervisor;  //ActivityStack的管理者ActivityStackSupervisor

    ActivityStack(ActivityStackSupervisor.ActivityContainer activityContainer, RecentTasks recentTasks) {
        mStackSupervisor = activityContainer.getOuter();
        ...
    }
}

mTaskHistory：是一個列表，存儲的是ActivityStack中的所有TaskRecord對象，TaskRecord 通過mActivities變量存儲Task中所有的Activity，所以mTaskHistory間接管理了ActivityStack中的所有activity；
mLRUActivities：一個列表，存儲的是ActivityStack中按照最近活動情況運行的所有Activity；

ActivityStackSupervisor

ActivityStackSupervisor 用於管理ActivityStack；ActivityStackSupervisor為AMS提供管理方法；管理着系統中的三個ActivityStack；

public final class ActivityStackSupervisor {/** The stack containing the launcher app. Assumed to always be attached to
     * Display.DEFAULT_DISPLAY. */
    private ActivityStack mHomeStack;

    /** The stack currently receiving input or launching the next activity. */
    private ActivityStack mFocusedStack;

    /** If this is the same as mFocusedStack then the activity on the top of the focused stack has
     * been resumed. If stacks are changing position this will hold the old stack until the new
     * stack becomes resumed after which it will be set to mFocusedStack. */
    private ActivityStack mLastFocusedStack;
        /** List of activities that are waiting for a new activity to become visible before completing
     * whatever operation they are supposed to do. */
    final ArrayList<ActivityRecord> mWaitingVisibleActivities = new ArrayList<ActivityRecord>();

    /** List of processes waiting to find out about the next visible activity. */
    final ArrayList<IActivityManager.WaitResult> mWaitingActivityVisible =
            new ArrayList<IActivityManager.WaitResult>();

    /** List of processes waiting to find out about the next launched activity. */
    final ArrayList<IActivityManager.WaitResult> mWaitingActivityLaunched =
            new ArrayList<IActivityManager.WaitResult>();

    /** List of activities that are ready to be stopped, but waiting for the next activity to
     * settle down before doing so. */
    final ArrayList<ActivityRecord> mStoppingActivities = new ArrayList<ActivityRecord>();

    /** List of activities that are ready to be finished, but waiting for the previous activity to
     * settle down before doing so.  It contains ActivityRecord objects. */
    final ArrayList<ActivityRecord> mFinishingActivities = new ArrayList<ActivityRecord>();

    /** List of activities that are in the process of going to sleep. */
    final ArrayList<ActivityRecord> mGoingToSleepActivities = new ArrayList<ActivityRecord>();
    ......    
    /** Mapping from (ActivityStack/TaskStack).mStackId to their current state */
    private SparseArray<ActivityContainer> mActivityContainers = new SparseArray<ActivityContainer>();//以mStackId為key

    /** Mapping from displayId to display current state */
    private final SparseArray<ActivityDisplay> mActivityDisplays =
            new SparseArray<ActivityDisplay>();//以displayId為key
}

AMS使用mHomeStack，mFocusedStack來完成系統全部的Activity的管理和調度。其中mHomeStack管理的是Launcher相關的任務，包括Launcher、RecentTask，Keyguad,除了上述以外的任務都歸mFocusedStack管理。

AMS 通過操作ActivityStackSupervisor來管理Activity；具體是如何操作的呢？ActivityStackSupervisor通過ActivityContainer來管理ActivityStack(ActivityStack的構造方法只有在ActivityContainer的構造方法中被調用)，ActivityContainer關聯ActivityDisplay，ActivityDisplay將自己的mStacks賦值給ActivityContainer的mStack；mStack.mStacks = activityDisplay.mStacks；

 

ActivityContainer

class ActivityContainer extends android.app.IActivityContainer.Stub {
        final static int FORCE_NEW_TASK_FLAGS = Intent.FLAG_ACTIVITY_NEW_TASK |
                Intent.FLAG_ACTIVITY_MULTIPLE_TASK | Intent.FLAG_ACTIVITY_NO_ANIMATION;
        final int mStackId;
        IActivityContainerCallback mCallback = null;
        final ActivityStack mStack; //ActivityContainer用於維護ActivityStack的
        ActivityRecord mParentActivity = null;
        String mIdString;

        boolean mVisible = true;

        /** Display this ActivityStack is currently on. Null if not attached to a Display. */
        ActivityDisplay mActivityDisplay;

        final static int CONTAINER_STATE_HAS_SURFACE = 0;
        final static int CONTAINER_STATE_NO_SURFACE = 1;
        final static int CONTAINER_STATE_FINISHING = 2;
        int mContainerState = CONTAINER_STATE_HAS_SURFACE;

        ActivityContainer(int stackId) {
            synchronized (mService) {
                mStackId = stackId;
                mStack = new ActivityStack(this);
                mIdString = "ActivtyContainer{" + mStackId + "}";
                if (DEBUG_STACK) Slog.d(TAG, "Creating " + this);
            }
        }

        void attachToDisplayLocked(ActivityDisplay activityDisplay) { 
        //ActivityContainer關聯ActivityDisplay，用
            if (DEBUG_STACK) Slog.d(TAG, "attachToDisplayLocked: " + this
                    + " to display=" + activityDisplay);
            mActivityDisplay = activityDisplay;
            mStack.mDisplayId = activityDisplay.mDisplayId;
            mStack.mStacks = activityDisplay.mStacks;

            activityDisplay.attachActivities(mStack);
            mWindowManager.attachStack(mStackId, activityDisplay.mDisplayId);
        }
......
------>/frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java

    /** Exactly one of these classes per Display in the system. Capable of holding zero or more
     * attached {@link ActivityStack}s */
    class ActivityDisplay {
        /** Actual Display this object tracks. */
        int mDisplayId;
        Display mDisplay;
        DisplayInfo mDisplayInfo = new DisplayInfo();

        /** All of the stacks on this display. Order matters, topmost stack is in front of all other
         * stacks, bottommost behind. Accessed directly by ActivityManager package classes */
        final ArrayList<ActivityStack> mStacks = new ArrayList<ActivityStack>();

        ActivityRecord mVisibleBehindActivity;

        ActivityDisplay() {
        }
        // After instantiation, check that mDisplay is not null before using this. The alternative
        // is for this to throw an exception if mDisplayManager.getDisplay() returns null.
        ActivityDisplay(int displayId) {
            final Display display = mDisplayManager.getDisplay(displayId);
            if (display == null) {
                return;
            }
            init(display);
        }
.......
        void attachActivities(ActivityStack stack) {
            if (DEBUG_STACK) Slog.v(TAG, "attachActivities: attaching " + stack + " to displayId="
                    + mDisplayId);
            mStacks.add(stack);
        }
......

追蹤代碼，發現ActivityContainer在ActivitySupervisor的createStackOnDisplay中被初始化，createStackOnDisplay在setWindowManager或adjustStackFocus或restoreRecentTaskLocked中被調用；這里說說從setWindowManager開始的調用流程，setWindowManager在SystemServer啟動AMS時調用，然后調用ActivityContainer.attachToDisplayLocked方法；流程的大概就是根據mDisplayId獲取ActivityDisplay，將ActivityDisplay的mStacks(代表該Display上的所有activitystack) 賦值給ActivityContainer的mStack的mStacks；同時將調用activityDisplay.attachActivities(mStack)將ActivityContainer的mStack(ActivityContainer維護的ActivityStack)添加到ActivityDisplay的mStacks 中；

ActivityStackSupervisor對ActivityRecord的管理過程如下：

ActivityStackSupervisor.mActivityDisplays
-> ActivityDisplay.mStacks
-> ActivityStack.mTaskHistory
-> TaskRecord.mActivities
-> ActivityRecord

 

二、場景解析

1、從桌面第一次啟動App

startActivityLocked里構造一個ActivityRecord
新建一個TaskRecord，並存入mTaskHistory
ActivityRecord存入mActivities

final int startActivityUncheckedLocked(...) {
    final int startActivityUncheckedLocked(...) {
    if (reuseTask == null) {
        r.setTask(targetStack.createTaskRecord(...);
        ...
        targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);
        ...
    }
}

1.TaskRecord存入mTaskHistory

 TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            boolean toTop) {
        TaskRecord task = new TaskRecord(mService, taskId, info, intent, voiceSession,
                voiceInteractor);
        addTask(task, toTop, false);
        return task;
    }

    void addTask(final TaskRecord task, final boolean toTop, boolean moving) {
        task.stack = this;
        if (toTop) {
            insertTaskAtTop(task, null);
        } else {
            mTaskHistory.add(0, task);
            updateTaskMovement(task, false);
        }
        ...
    }

    private void insertTaskAtTop(TaskRecord task, ActivityRecord newActivity) {
        ...
        mTaskHistory.add(taskNdx, task);
        updateTaskMovement(task, true);
    }

2.ActivityRecord存入mActivities

final void startActivityLocked(ActivityRecord r, boolean newTask, ...) {
    ...
    task = mTaskHistory.get(taskNdx);
    ...
    task.addActivityToTop(r);
}
void addActivityToTop(ActivityRecord r) {
    addActivityAtIndex(mActivities.size(), r);
}
void addActivityAtIndex(int index, ActivityRecord r) {
    ...
    mActivities.add(index, r);
    ...
}