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

讯享网

• 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

讯享网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

讯享网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。

讯享网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

讯享网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

讯享网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

讯享网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

讯享网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); } }