Android4.4 Framework分析——ActivityManagerService的启动和对Activity的管理

本文主要介绍android4.4中ActivityManagerService的启动和ActivityManagerService对Activity堆栈的管理。

一、ActivityManagerService的启动

ActivityManagerService也是在SystemServer启动的时候创建的，

class ServerThread {    .......   public void initAndLoop() {    ......    context = ActivityManagerService.main(factoryTest); //启动AMS    .......    ActivityManagerService.setSystemProcess(); //向Service Manager注册    .......   } }

需要在一个新线程中初始化ActivityManagerService，ActivityManagerService用了单例模式。

 public static final Context main(int factoryTest) {        AThread thr = new AThread();        thr.start(); //启动一个线程来启动        synchronized (thr) {            while (thr.mService == null) {                try {                    thr.wait();//线程等待activitymanagerservice初始化完成                } catch (InterruptedException e) {                }            }        }        ActivityManagerService m = thr.mService;        mSelf = m;        ActivityThread at = ActivityThread.systemMain(); //启动一个主线程        mSystemThread = at;        Context context = at.getSystemContext();        context.setTheme(android.R.style.Theme_Holo);         ......        m.mStackSupervisor = new ActivityStackSupervisor(m, context, thr.mLooper); //新建一个activity堆栈管理辅助类实例        .......        synchronized (thr) {            thr.mReady = true;            thr.notifyAll(); //activitymanagerservice启动完成        }        m.startRunning(null, null, null, null);        return context;    }

二、ActivityStackSupervisor和ActivityStack管理Activity的状态

1.ActivityState

描述一个Activity可能经历的所有状态，定义在ActivityStack.java文件中：

    enum ActivityState {        INITIALIZING, //正在初始化        RESUMED, //已经恢复        PAUSING, //正在暂停        PAUSED, //已经暂停        STOPPING, //正在停止        STOPPED, //已经停止        FINISHING, //正在完成        DESTROYING, //正在销毁        DESTROYED //已经销毁    }

 状态变换图:

    /**     * The back history of all previous (and possibly still     * running) activities.  It contains #TaskRecord objects.     */    private ArrayList<TaskRecord> mTaskHistory = new ArrayList<TaskRecord>();    /**     * Used for validating app tokens with window manager.     */    final ArrayList<TaskGroup> mValidateAppTokens = new ArrayList<TaskGroup>();    /**     * 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<ActivityRecord>();    /**     * Animations that for the current transition have requested not to     * be considered for the transition animation.     */    final ArrayList<ActivityRecord> mNoAnimActivities = new ArrayList<ActivityRecord>();    /**     * 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;

ActivityRecord变量的具体含义，可查看注释。

2.记录Activity的ArrayList和ActivityStack

    /** The stack containing the launcher app */    private ActivityStack mHomeStack;    /** The non-home stack currently receiving input or launching the next activity. If home is     * in front then mHomeStack overrides mFocusedStack.     * DO NOT ACCESS DIRECTLY - It may be null, use getFocusedStack() */    private ActivityStack mFocusedStack;    /** All the non-launcher stacks */    private ArrayList<ActivityStack> mStacks = new ArrayList<ActivityStack>();

mHomeStack : 只记录存放Launcher和SystemUI(最近应用)的Task

mFocusedStack ： 记录所有非Launcher App的Task

mStacks : 这个ArrayList只存放mHomeStack和mFocusedStack，mHomeStack放在第0个位置

这个结果我是在用adb shell dumpsys activity命令查看而得知：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)   Stack #0:     Task id #1       TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}       Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10200000 cmp=com.android.launcher/com.android.launcher2.Launcher }         Hist #0: ActivityRecord{b2214570 u0 com.android.launcher/com.android.launcher2.Launcher t1}           Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher }           ProcessRecord{b21df5c8 1402:com.android.launcher/u0a8}     Task id #3       TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}       Intent { act=com.android.systemui.recent.action.TOGGLE_RECENTS flg=0x10800000 cmp=com.android.systemui/.recent.RecentsActivity bnds=[132,331][296,476] (has extras) }         Hist #0: ActivityRecord{b22d5aa0 u0 com.android.systemui/.recent.RecentsActivity t3}           Intent { act=com.android.systemui.recent.action.TOGGLE_RECENTS flg=0x10800000 cmp=com.android.systemui/.recent.RecentsActivity bnds=[132,331][296,476] (has extras) }           ProcessRecord{b2169ac8 1313:com.android.systemui/u0a7}      Running activities (most recent first):       TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}         Run #1: ActivityRecord{b2214570 u0 com.android.launcher/com.android.launcher2.Launcher t1}       TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}         Run #0: ActivityRecord{b22d5aa0 u0 com.android.systemui/.recent.RecentsActivity t3}    Stack #1:     Task id #4       TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}       Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.contacts/.activities.PeopleActivity }         Hist #0: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}           Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.contacts/.activities.PeopleActivity bnds=[64,417][128,481] }           ProcessRecord{b22f66c0 1820:com.android.contacts/u0a2}      Task id #2       TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}       Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.dialer/.DialtactsActivity }         Hist #0: ActivityRecord{b223d3c8 u0 com.android.dialer/.DialtactsActivity t2}           Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.dialer/.DialtactsActivity bnds=[0,417][64,481] }           ProcessRecord{b2215d48 1569:com.android.dialer/u0a4}      Running activities (most recent first):       TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}         Run #1: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}       TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}         Run #0: ActivityRecord{b223d3c8 u0 com.android.dialer/.DialtactsActivity t2}      mResumedActivity: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}    mFocusedActivity: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}   mDismissKeyguardOnNextActivity:false   mStackState=STACK_STATE_HOME_IN_BACK   mSleepTimeout: false   mCurTaskId: 4   mUserStackInFront: {}    Recent tasks:   * Recent #0: TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}   * Recent #1: TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}   * Recent #2: TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}   * Recent #3: TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}

Stack #0 就是mHomeStack，里面放了Launcher和SystemUI的task。

Stack #1 就是mFocusedStack，放了所有已经启动的app的task。

这两个就是mStacks里面存放的。

3.现在看看mHomeStack和mFocusedStack是什么时候被放入mStacks里的？mHomeStack和mFocusedStack里面的元素是在哪里加入的？

     mHomeStack的初始化是在开机时，WindowManagerService创建完成后，ActivityManagerService设置WindowManagerService时，

            ActivityManagerService.self().setWindowManager(wm); //SystemServer.java中

    public void setWindowManager(WindowManagerService wm) { //<font size="4"><font size="4"><font size="4"><span style="font-size:18px;"><span style="font-size:18px;"><span style="font-size:18px;">ActivityManagerService</span></span></span></font></font>.java</font>中        mWindowManager = wm;        mStackSupervisor.setWindowManager(wm);        wm.createStack(HOME_STACK_ID, -1, StackBox.TASK_STACK_GOES_OVER, 1.0f);    }

    void setWindowManager(WindowManagerService wm) { //ActivityStackSupervisor.java中        mWindowManager = wm;        mHomeStack = new ActivityStack(mService, mContext, mLooper, HOME_STACK_ID);        mStacks.add(mHomeStack); //放在了第0个位置    }

 mFocusedStack存放的是应用程序的task，所以它的创建是在Activity启动的时候，Activity的启动过程可以参考Android4.4 framework分析——Launcher中启动应用程序(startActivity)的过程step16，startActivityUncheckedLocked()中，

        if (r.resultTo == null && !addingToTask                && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {            targetStack = adjustStackFocus(r); //targetStack即目标Stack，r要加入的stack

    ActivityStack adjustStackFocus(ActivityRecord r) {        final TaskRecord task = r.task;        //r是否是应用程序的activity类型，或者r所属task是应用程序task        //android定义区分了三种不同的activity类型        //static final int APPLICATION_ACTIVITY_TYPE = 0; //应用程序类型        //static final int HOME_ACTIVITY_TYPE = 1; //Launcher类型        //static final int RECENTS_ACTIVITY_TYPE = 2; //SystemUI的最近应用        if (r.isApplicationActivity() || (task != null && task.isApplicationTask())) {             if (task != null) {                if (mFocusedStack != task.stack) {                    if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG,                            "adjustStackFocus: Setting focused stack to r=" + r + " task=" + task);                    mFocusedStack = task.stack;                } else {                    if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG,                        "adjustStackFocus: Focused stack already=" + mFocusedStack);                }                return mFocusedStack;//app类型的activity每次都加入mFocusedStack            }            if (mFocusedStack != null) {                if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG,                        "adjustStackFocus: Have a focused stack=" + mFocusedStack);                return mFocusedStack;//app类型的activity每次都加入mFocusedStack            }            for (int stackNdx = mStacks.size() - 1; stackNdx > 0; --stackNdx) {                ActivityStack stack = mStacks.get(stackNdx);                if (!stack.isHomeStack()) {                    if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG,                            "adjustStackFocus: Setting focused stack=" + stack);                    mFocusedStack = stack;                    return mFocusedStack;//app类型的activity每次都加入mFocusedStack                }            }            // Time to create the first app stack for this user.            int stackId = mService.createStack(-1, HOME_STACK_ID, //启动第一个app，需要创建一个stack，其他app创建时，前面条件判断将拦截住                StackBox.TASK_STACK_GOES_OVER, 1.0f);            if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: New stack r=" + r +                    " stackId=" + stackId);            mFocusedStack = getStack(stackId);            return mFocusedStack; //app类型的activity每次都加入mFocusedStack        }        return mHomeStack;    }

从上面这个方法看出，Launcher类型和最近应用类型的task将加入mHomeStack中，而其他应用类型的task加入mFocusedStack，

    public int createStack(int taskId, int relativeStackBoxId, int position, float weight) {        enforceCallingPermission(android.Manifest.permission.MANAGE_ACTIVITY_STACKS,                "createStack()");        synchronized (this) {            long ident = Binder.clearCallingIdentity();            try {                int stackId = mStackSupervisor.createStack(); //看这里                mWindowManager.createStack(stackId, relativeStackBoxId, position, weight);                if (taskId > 0) {                    moveTaskToStack(taskId, stackId, true);                }                return stackId;            } finally {                Binder.restoreCallingIdentity(ident);            }        }    }</span>

<span style="font-size:18px;">    int createStack() {         while (true) {            if (++mLastStackId <= HOME_STACK_ID) {                mLastStackId = HOME_STACK_ID + 1;            }            if (getStack(mLastStackId) == null) {                break;            }        }        mStacks.add(new ActivityStack(mService, mContext, mLooper, mLastStackId)); //新建了一个Stack加入mStacks        return mLastStackId;    }

createStack()方法只有一次机会执行，即第一次运行app。

mStacks里什么情况下会出现第三或第四个元素，这个不知道，目前没有发现这种情况。。。

未完待续，有不对的地方，请指正。