【framework】ATMS启动流程

1 前言

​ ATMS 即 ActivityTaskManagerService，用于管理 Activity 及其容器（任务、堆栈、显示等）。ATMS 在 Android 10 中才出现，由原来的 AMS（ActivityManagerService）分离而来，承担了 AMS 的部分职责。因此，在 AMS初始化过程中（AMS启动流程），也伴随着了 ATMS 的初始化。本文主要介绍 ATMS 的启动流程和初始化过程。

​ （1）ATMS 创建流程

• SystemServer：依次调用 main()、run()、startBootstrapServices()，再调用 SystemServiceManager 的 startService() 方法，并将 Lifecyle.class 传入；
• SystemServiceManager ：startService() 方法通过反射调用 Lifecyle 的构造方法，生成 Lifecyle 对象；
• Lifecyle：构造方法中调用 ATMS 的构造方法创建 ATMS 对象，并通过 getService() 方法返回 ATMS 对象。

​ （2）ATMS 初始化

​ 如图，ATMS 在初始化时创建了图中蓝色类的对象。

2 ATMS 启动流程

​ （1）main

​ /frameworks/base/services/java/com/android/server/SystemServer.java

public static void main(String[] args) {
    new SystemServer().run();
}

​ （2）run

​ /frameworks/base/services/java/com/android/server/SystemServer.java

private void run() {
	try {
		...
		// 创建Looper
		Looper.prepareMainLooper();
		// 加载libandroid_servers.so
		System.loadLibrary("android_servers");
		// 创建系统的 Context：ContextImpl.createSystemContext(new ActivityThread())
		createSystemContext();
		// 创建 SystemServiceManager
		mSystemServiceManager = new SystemServiceManager(mSystemContext);
		LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
		...
	}
	...
	try {
		//启动引导服务，ActivityManagerService、ActivityTaskManagerService、PackageManagerService、PowerManagerService、DisplayManagerService 等
		startBootstrapServices();
		//启动核心服务，BatteryService、UsageStatusService 等
		startCoreServices();
		//启动其他服务，InputManagerService、WindowManagerService、CameraService、AlarmManagerService 等
		startOtherServices();
		...
	}
	...
	// 开启消息循环
	Looper.loop();
}

​ （3）startBootstrapServices

​ /frameworks/base/services/java/com/android/server/SystemServer.java

private void startBootstrapServices() {
	...
    //启动 ATMS
	ActivityTaskManagerService atm = mSystemServiceManager.startService(ActivityTaskManagerService.Lifecycle.class).getService();
    //启动 AMS，并将 ATMS 注入
	mActivityManagerService = ActivityManagerService.Lifecycle.startService(mSystemServiceManager, atm);
	...
}

​ （4）startService

​ /frameworks/base/services/core/java/com/android/server/SystemServiceManager.java

public <T extends SystemService> T startService(Class<T> serviceClass) {
	try {
		final String name = serviceClass.getName();
		...
		final T service;
		try { //通过反射调用 serviceClass 的构造方法 创建 Lifecycle 对象
			Constructor<T> constructor = serviceClass.getConstructor(Context.class);
			service = constructor.newInstance(mContext);
		}
		...
		startService(service);
		return service;
	}
	...
}

public void startService(SystemService service) {
	mServices.add(service); //mServices: ArrayList<SystemService>
	...
	try {
		service.onStart(); //调用 Lifecycle 的 onStart 方法
	}
	...
}

​ （5）ATMS.Lifecycle

/frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.Lifecycle.java

public static final class Lifecycle extends SystemService {
	private final ActivityTaskManagerService mService;

	public Lifecycle(Context context) {//被 SystemServiceManager 的 startService() 方法调用
		super(context);
		mService = new ActivityTaskManagerService(context);
	}

	public void onStart() {
        //添加 ATMS 服务，方便跨进程调用：ServiceManager.addService(Context.ACTIVITY_TASK_SERVICE, mService, false, DUMP_FLAG_PRIORITY_DEFAULT)
		publishBinderService(Context.ACTIVITY_TASK_SERVICE, mService);
		mService.start(); //调用 ATMS 的 start() 方法
	}

	...

	public ActivityTaskManagerService getService() {
		return mService;
	}
}

​ 注意：onStart() 方法中调用 ATMS 的 start() 方法初始化（下文还会介绍）。 已通过 ServiceManager.addService() 将 Context.ACTIVITY_TASK_SERVICE 与 ATMS 绑定，因此在其他进程中可以通过如下方式获取 ATMS。

IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
IActivityTaskManager atm = IActivityTaskManager.Stub.asInterface(b);

3 ATMS 初始化

​ （1）ATMS 的构造方法

​ /frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

public ActivityTaskManagerService(Context context) {
	mContext = context;
	...
	mSystemThread = ActivityThread.currentActivityThread();
	mUiContext = mSystemThread.getSystemUiContext(); //ContextImpl.createSystemUiContext(getSystemContext())
	mLifecycleManager = new ClientLifecycleManager();
	mInternal = new LocalService(); //ActivityTaskManagerInternal 的子类
	...
}

​ （2）start

​ start() 方法被 Lifecycle 的 onStart() 方法调用，onStart() 方法又被 SystemServiceManager 的 startService() 方法调用。

​ /frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

private void start() {
	LocalServices.addService(ActivityTaskManagerInternal.class, mInternal);
}

​ mInternal 属于 LocalService 类（ActivityTaskManagerInternal 的子类），在 ATMS 的构造方法中创建。

​ （3）initialize

​ 在 AMS 的构造方法中，调用了 ATMS 的 initialize() 方法进一步初始化。

​ /frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
	...
	mHandlerThread = new ServiceThread(TAG, THREAD_PRIORITY_FOREGROUND, false);
    ...
    mUserController = new UserController(this);
	mPendingIntentController = new PendingIntentController(mHandlerThread.getLooper(), mUserController);
	...
	mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);
	mActivityTaskManager = atm;
	//进一步初始化 ATMS
	mActivityTaskManager.initialize(mIntentFirewall, mPendingIntentController, DisplayThread.get().getLooper());
	...
}

​ /frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

public void initialize(IntentFirewall intentFirewall, PendingIntentController intentController, Looper looper) {
	mH = new H(looper);
	mUiHandler = new UiHandler();
	mIntentFirewall = intentFirewall;
	...
	mPendingIntentController = intentController;
	mTempConfig.setToDefaults(); //定义时即被创建：mTempConfig = new Configuration()
	...
	//new ActivityStackSupervisor(this, mH.getLooper())
	mStackSupervisor = createStackSupervisor();
	mRootActivityContainer = new RootActivityContainer(this);
	mRootActivityContainer.onConfigurationChanged(mTempConfig);
	...
	mLockTaskController = new LockTaskController(mContext, mStackSupervisor, mH);
	mActivityStartController = new ActivityStartController(this);
	mRecentTasks = createRecentTasks(); //new RecentTasks(this, mStackSupervisor)
	mStackSupervisor.setRecentTasks(mRecentTasks);
	...
}

​ （4）onActivityManagerInternalAdded

​ 在 AMS 的 start() 方法中，调用了 ATMS 的 onActivityManagerInternalAdded() 方法进一步初始化。

​ /frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

private void start() {
	...
	LocalServices.addService(ActivityManagerInternal.class, new LocalService());
    //调用 ATMS 的 onActivityManagerInternalAdded 方法进一步初始化
	mActivityTaskManager.onActivityManagerInternalAdded();
	mUgmInternal.onActivityManagerInternalAdded();
	mPendingIntentController.onActivityManagerInternalAdded();
	...
}

​ /frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

public void onActivityManagerInternalAdded() {
	synchronized (mGlobalLock) {
		mAmInternal = LocalServices.getService(ActivityManagerInternal.class);
		mUgmInternal = LocalServices.getService(UriGrantsManagerInternal.class);
	}
}

​ （5）ActivityStartController

​ ActivityStartController 作为 ATMS 的一个重要成员，控制了 Activity 的启动，因此我们继续跟进 ActivityStartController 的构造方法。

​ /frameworks/base/services/core/java/com/android/server/am/ActivityStartController.java

ActivityStartController(ActivityTaskManagerService service) {
	this(service, service.mStackSupervisor,
			new DefaultFactory(service, service.mStackSupervisor,
				new ActivityStartInterceptor(service, service.mStackSupervisor)));
}

ActivityStartController(ActivityTaskManagerService service, ActivityStackSupervisor supervisor,
		Factory factory) {
	mService = service;
	mSupervisor = supervisor;
	mHandler = new StartHandler(mService.mH.getLooper());
	mFactory = factory;
	mFactory.setController(this);
	...
}

​ （6）DefaultFactory

​ DefaultFactory 是 ActivityStarter 的静态内部类，负责 ActivityStarter 的创建和回收。因此我们继续跟进 DefaultFactory 类。

​ /frameworks/base/services/core/java/com/android/server/wm/ActivityStarter.DefaultFactory.java

static class DefaultFactory implements Factory {
	...
	private ActivityStartController mController;
	private ActivityTaskManagerService mService;
	private ActivityStackSupervisor mSupervisor;
	private ActivityStartInterceptor mInterceptor;

	//MAX_STARTER_COUNT = 3
	private SynchronizedPool<ActivityStarter> mStarterPool = new SynchronizedPool<>(MAX_STARTER_COUNT);

	DefaultFactory(ActivityTaskManagerService service, ActivityStackSupervisor supervisor, ActivityStartInterceptor interceptor) {
		mService = service;
		mSupervisor = supervisor;
		mInterceptor = interceptor;
	}

	public ActivityStarter obtain() {
		ActivityStarter starter = mStarterPool.acquire();
		if (starter == null) {
			starter = new ActivityStarter(mController, mService, mSupervisor, mInterceptor);
		}
		return starter;
	}

	@Override
	public void recycle(ActivityStarter starter) {
		mStarterPool.release(starter);
	}
}