AndroidT(13) --ActivityTaskManagerService 和 ActivityManagerService 的初始化(一)

1.概览

  ATMS在我看来属于AMS的一个辅助类，剥离了AMS中的一些功能到ATMS，下面引用官方的简单说明

System service for managing activities and their containers (task, displays,... ).

2.ActivityTaskManagerService 的实例化

//frameworks/base/services/java/com/android/server/SystemServer.java
startBootstrapServices
    ActivityTaskManagerService atm = mSystemServiceManager.startService(ActivityTaskManagerService.Lifecycle.class).getService();

  根据SystemServiceManager章节的分析可知 startService(ActivityTaskManagerService.Lifecycle.class) 对应代码如下

startService(ActivityTaskManagerService.Lifecycle.class)
    Lifecycle(Context context)
        //code 1
        super(context);
        //code 2
        mService = new ActivityTaskManagerService(context);
            ...
            mInternal = new LocalService();//final ActivityTaskManagerInternal mInternal;
    ActivityTaskManagerService.Lifecycle.onStart()
        //code 3
        publishBinderService(Context.ACTIVITY_TASK_SERVICE, mService);
        //code 4
        mService.start();// mService type is ActivityTaskManagerService
        ||
        LocalServices.addService(ActivityTaskManagerInternal.class, mInternal);

2.1 code 1–记录Context

  父类 SystemService 在构造的时候会记录下传入的Context，获取的时候可以使用 getContext。

2.2 code2–实例化ActivityTaskManagerService

public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
    public ActivityTaskManagerService(Context context) {
        mContext = context;
        mFactoryTest = FactoryTest.getMode();
        mSystemThread = ActivityThread.currentActivityThread();
        mUiContext = mSystemThread.getSystemUiContext();
        mLifecycleManager = new ClientLifecycleManager();
        mVisibleActivityProcessTracker = new VisibleActivityProcessTracker(this);
        mInternal = new LocalService();
        GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version", GL_ES_VERSION_UNDEFINED);
        mWindowOrganizerController = new WindowOrganizerController(this);
        mTaskOrganizerController = mWindowOrganizerController.mTaskOrganizerController;
        mTaskFragmentOrganizerController =
                mWindowOrganizerController.mTaskFragmentOrganizerController;
        mBackNavigationController = BackNavigationController.isEnabled()
                ? new BackNavigationController() : null;
    }
}

  这里就只展开一级代码，主要注意下 mInternal，因为最终调用ATMS的接口实现大都位于 mInternal 即 LocalService。至于其他变量的的作用放到具体的场景再涉及，此处先关注调用流程相关的部分。

2.3 code 3–公开服务ActivityTaskManagerService

//frameworks/base/services/core/java/com/android/server/SystemService.java
publishBinderService(Context.ACTIVITY_TASK_SERVICE, mService)
    publishBinderService(name, service, false);
        publishBinderService(name, service, allowIsolated, DUMP_FLAG_PRIORITY_DEFAULT);
            ServiceManager.addService(name, service, allowIsolated, dumpPriority);

  在设置了一些标志位之后，最终的实现还是调用ServiceManager.addService 想系统中注册本ATM服务，如此其他有权限的用户就可以通过 ACTIVITY_TASK_SERVICE 服务名来跨进程调用ATM服务了。注意了注册进去的服务实例在code2处实例化，

mService = new ActivityTaskManagerService(context);

2.4 code 4–注册ATM服务的内部实现

  前面提到过ATM服务的接口实现，最终是调用到 mInternal 的即内部类 LocalService 。这一步和上面提到的ATM服务的注册作用是一样的，只是一个用于支持跨进程，另一个用于本进程内部使用。显然，进程内部调用是没必要走跨进程流程的，所以直接注册 LocalService 的实例而非 ATM服务的实例。下面看下 LocalService.add 的实现

//frameworks/base/core/java/com/android/server/LocalServices.java
public static <T> void addService(Class<T> type, T service) {
    synchronized (sLocalServiceObjects) {
        if (sLocalServiceObjects.containsKey(type)) {
            throw new IllegalStateException("Overriding service registration");
        }
        sLocalServiceObjects.put(type, service);
    }
}

  sLocalServiceObjects 的定义如下，其位静态私有变量属于类

//frameworks/base/core/java/com/android/server/LocalServices.java
private static final ArrayMap<Class<?>, Object> sLocalServiceObjects =
        new ArrayMap<Class<?>, Object>();

  然后使用类作为key，对应类的实例化作为value进行存储。在本进程内可以调用 getService 来获取对应的实例。

3.ActivityManagerService.Lifecycle 的实例化

  AMS的启动也ATMS类似，都是始于SystemServer，位于system_server 进程中，下面是对应的代码

//frameworks/base/services/java/com/android/server/SystemServer.java
//private ActivityManagerService mActivityManagerService;
mActivityManagerService = ActivityManagerService.Lifecycle.startService(mSystemServiceManager, atm);
    sAtm = atm;
    return ssm.startService(ActivityManagerService.Lifecycle.class).getService();

  ssm也就是SystemServer侧传递过来的 SystemServiceManager ，根据SystemServiceManager章节的分析可知 ssm.startService等同如下

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
ssm.startService(ActivityManagerService.Lifecycle.class)
    Lifecycle(Context context)
        super(context);
        mService = new ActivityManagerService(context, sAtm);
            ...
            mInternal = new LocalService();
    onStart
        mService.start();//mService type is ActivityManagerService
            mBatteryStatsService.publish();
            mAppOpsService.publish();
            mProcessStats.publish();
            LocalServices.addService(ActivityManagerInternal.class, mInternal);
            LocalManagerRegistry.addManager(ActivityManagerLocal.class,
                    (ActivityManagerLocal) mInternal);
            mActivityTaskManager.onActivityManagerInternalAdded();
            mPendingIntentController.onActivityManagerInternalAdded();
            mAppProfiler.onActivityManagerInternalAdded();
            CriticalEventLog.init();

  和ATMS的套路是一致的，这里也只展开一层的调用。不过需要注意下 mInternal，其为 LocalService 的实例，

public final class LocalService extends ActivityManagerInternal
        implements ActivityManagerLocal {

}

  因此，client调用到AMS的时候，大部分的实现都是 mInternal 实现的。此处主要注意下调用流程。