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，

<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 #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
}

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。