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，
<span style="font-size:18px;">class ServerThread {.......public void initAndLoop() {......context = ActivityManagerService.main(factoryTest); //启动AMS.......ActivityManagerService.setSystemProcess(); //向Service Manager注册.......}}</span>
需要在一个新线程中初始化ActivityManagerService，ActivityManagerService用了单例模式。
<span style="font-size:18px;"> 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;}</span>
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 #1TaskRecord{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 #3TaskRecord{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 #4TaskRecord{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 #2TaskRecord{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:falsemStackState=STACK_STATE_HOME_IN_BACKmSleepTimeout: falsemCurTaskId: 4mUserStackInFront: {}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}
Android4.4 framework分析——Launcher中启动应用程序(startActivity)的过程
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);} } }
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。
