AMS-ATMS 启动/初始化

AMS-ATMS 启动/初始化

AMS 的启动流程代码展示：

• 调用startBootstrapServices,开启服务

//frameworks/base/services/java/com/android/server/SystemServer.java
private void run() {
  ...
  // Start services.
  try {
      t.traceBegin("StartServices");
      // 在startBootstrapServices里面开启AMS服务
      startBootstrapServices(t);
      startCoreServices(t);
      // WMS在这里启动，启动之后会将WMS放入到AMS以及ATMS中
      startOtherServices(t);
      checkAccessGranted(mSystemContext);
  } catch (Throwable ex) {
      Slog.e("System", "******************************************");
      Slog.e("System", "************ Failure starting system services", ex);
      throw ex;
  } finally {
      t.traceEnd(); // StartServices
  }
  ...
}

• ATMS ，是Android核心服务，在Android 新版本中，activity的调度和管理已经从AMS移到了ActivityTaskManagerService中，ATMS 调度的不仅仅是Activity，还包括其容器(task、stacks、displays等)，AMS负责四大组件中另外3个(service, broadcast, contentprovider)的管理和调度

• ATMS并不是直接启动，而是通过 Lifecycle 来间接实现，Lifecycle 是 ATMS 里的静态内部类，静态内部类不依赖于外部类，不会隐式持有外部类的引用，Lifecycle 构造方法调用时，会初始化内部成员变量 mService，即调用ATMS的构造方法，构造方法中会执行一些初始化操作.

//frameworks/base/services/java/com/android/server/SystemServer.java
private void startBootstrapServices(@NonNull TimingsTraceAndSlog t) {
  ...
  t.traceBegin("StartActivityManager");
  // 启动ATMS
  ActivityTaskManagerService atm = mSystemServiceManager.startService(
          ActivityTaskManagerService.Lifecycle.class).getService();
  // 启动AMS,ATMS被放入到了AMS中
  mActivityManagerService = ActivityManagerService.Lifecycle.startService(
          mSystemServiceManager, atm);
  mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
  mActivityManagerService.setInstaller(installer);
  mWindowManagerGlobalLock = atm.getGlobalLock();
  t.traceEnd();
  ...
}

• AMS 与ATMS 的启动方法十分相似,都是调用了ssm中的startService 方法，通过反射的方式初始化.我们可以发现，实际上AMS 初始化的是AMSE，它是继承AMS类的，ATMS被放在了AMS中保存起来.

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public Lifecycle(Context context) {
      super(context);
      // AMTS内部Lifecycle类的构造方法
      mService = new ActivityTaskManagerService(context);
      // AMS内部Lifecycle类的构造方法
      mService = new ActivityManagerServiceEx(context, sAtm);
  }

• AMS 初始化部分重要细节

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
    ...
    mContext = systemContext;
    ...
    mSystemThread = ActivityThread.currentActivityThread();
    mUiContext = mSystemThread.getSystemUiContext();
    //AMS 处理消息的Handler
    mHandlerThread = new ServiceThread(TAG,
            THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
    mHandlerThread.start();
    mHandler = new MainHandler(mHandlerThread.getLooper());
    //UI handler
    mUiHandler = mInjector.getUiHandler(this);
    ....
    //初始化3种广播队列，前台，后台 offload
    mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "foreground", foreConstants, false);
    mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "background", backConstants, true);
    mOffloadBroadcastQueue = new BroadcastQueue(this, mHandler,
            "offload", offloadConstants, true);
    ...
    mServices = new ActiveServicesEx(this);
    ...
    //初始化ATMS
    mActivityTaskManager = atm;
    //在此方法中，初始化了ActivityStackSupervisor，它是用来管理所有activity的.
    mActivityTaskManager.initialize(mIntentFirewall, mPendingIntentController,
            DisplayThread.get().getLooper());
    //CPU监控器了~开启一个线程循环检测CPU使用状态
    mProcessCpuThread = new Thread("CpuTracker") {
        @Override
        public void run() {
          ...
        }
    };
    // 加入看门狗
    Watchdog.getInstance().addMonitor(this);
    Watchdog.getInstance().addThread(mHandler);
}

• ATMS 初始化做的那些事

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
    ...
    //将生成的ATMS 赋值给AMS的变量mActivityTaskManager,随后调用ATMS的initialize函数进行初始化
    mActivityTaskManager = atm;
    mActivityTaskManager.initialize(mIntentFirewall, mPendingIntentController,
    ...
}

//frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
public void initialize(IntentFirewall intentFirewall, PendingIntentController intentController,
        Looper looper) {
    //初始化了两个handler去处理一些事物
    mH = new H(looper);
    mUiHandler = new UiHandler();
    ...
    // 注意下这里,实质上Activity 的调度和管理由mStackSupervisor处理
    mStackSupervisor = createStackSupervisor();

    //  mTaskChangeNotificationController内部是一个handler，用来做task相关变化需要处理的事物
    mTaskChangeNotificationController =
            new TaskChangeNotificationController(mGlobalLock, mStackSupervisor, mH);
    //初始化最近任务栈,也将mStackSupervisor中的RecentTasks进行了设置
    setRecentTasks(new RecentTasks(this, mStackSupervisor));
    ...
}

protected ActivityStackSupervisor createStackSupervisor() {
    final ActivityStackSupervisor supervisor = new ActivityStackSupervisor(this, mH.getLooper());
    // 这里调用了supervisor的初始化
    supervisor.initialize();
    return supervisor;
}

• ActivityStackSupervisor 初始化

//frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
public void initialize() {
    // 确保supervisor只会初始化一次
    if (mInitialized) {
        return;
    }

    mInitialized = true;
    // 初始化RunningTasks,里面包含了所有正在运行的tasks.
    setRunningTasks(new RunningTasks());
    ...
}