1、C/S

framework层关键的代码可见此链接

服务端关键类

frameworks/base/services/java/com/android/server/
  - SystemServer.java  -- vm通过main方法启动服务端
frameworks/base/services/core/java/com/android/server/
  - SystemServiceManager.java -- 全部系统服务的管理类
  - ServiceThread.java
  - pm/Installer.java
  - am/ActivityManagerService.java -- AMS关键服务类

客户端关键类

frameworks/base/core/java/android/app/
  - ActivityThread.java -- vm通过main方法启动客户端
  - LoadedApk.java
  - ContextImpl.java

2、S启动过程

2.1、SystemServer#main

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

2.2、SystemServer#run

// Initialize the system context.
createSystemContext(); 这里通过ActivityThread.systemMain()创建ActivityThread获取Context

// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
。。。。
 startBootstrapServices();
 startCoreServices();
 startOtherServices();
。。。。

SystemServer#startBootstrapServices

启动启动系统必要的关键service

private void startBootstrapServices() {
...
    Installer installer = mSystemServiceManager.startService(Installer.class);
...
    mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
...
//通过mSystemServiceManager反射创建LifeCycle，从而创建AMS
    mActivityManagerService = mSystemServiceManager.startService(
            ActivityManagerService.Lifecycle.class).getService();
//相当于 Lifecycle.getService
    mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
    mActivityManagerService.setInstaller(installer);
.....
     mActivityManagerService.setSystemProcess(); //设置系统进程
...
}

SystemServiceManager.startService(ActivityManagerService.Lifecycle.class) 功能主要：

1. 创建ActivityManagerService.Lifecycle对象，从而创建AMS

2. 调用Lifecycle.onStart()方法

ActivityManagerService#Lifecycle构造方法

public static final class Lifecycle extends SystemService {
    private final ActivityManagerService mService;
    public Lifecycle(Context context) {
        super(context);
//内部创建AMS
        mService = new ActivityManagerService(context);
    }
    @Override
    public void onStart() {
        mService.start();
    }

AMS创建

public ActivityManagerService(Context systemContext) {
    mContext = systemContext;
    mFactoryTest = FactoryTest.getMode();//默认为FACTORY_TEST_OFF
    mSystemThread = ActivityThread.currentActivityThread();

    //1、创建名为"ActivityManager"的前台线程，也就是UI线程，只许system设置，并获取mHandler
    mHandlerThread = new ServiceThread(TAG, android.os.Process.THREAD_PRIORITY_FOREGROUND, false);
    mHandlerThread.start();

    mHandler = new MainHandler(mHandlerThread.getLooper());

    //2、通过UiThread类，创建名为"android.ui"的线程
    mUiHandler = new UiHandler();

    //前台广播接收器，在运行超过10s将放弃执行
    mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "foreground", BROADCAST_FG_TIMEOUT, false);
    //后台广播接收器，在运行超过60s将放弃执行
    mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "background", BROADCAST_BG_TIMEOUT, true);
    mBroadcastQueues[0] = mFgBroadcastQueue;
    mBroadcastQueues[1] = mBgBroadcastQueue;

    //创建ActiveServices，其中非低内存手机mMaxStartingBackground为8
    mServices = new ActiveServices(this);
    mProviderMap = new ProviderMap(this);

    //创建目录/data/system
    File dataDir = Environment.getDataDirectory();
    File systemDir = new File(dataDir, "system");
    systemDir.mkdirs();

    //创建服务BatteryStatsService
    mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
    mBatteryStatsService.getActiveStatistics().readLocked();
    ...

    //创建进程统计服务，信息保存在目录/data/system/procstats，
    mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));

    mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);
    mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));

    // User 0是第一个，也是唯一的一个开机过程中运行的用户
    mStartedUsers.put(UserHandle.USER_OWNER, new UserState(UserHandle.OWNER, true));
    mUserLru.add(UserHandle.USER_OWNER);
    updateStartedUserArrayLocked();
    ...

    //CPU使用情况的追踪器执行初始化
    mProcessCpuTracker.init();
    ...
    mRecentTasks = new RecentTasks(this);
    // 创建ActivityStackSupervisor对象
    mStackSupervisor = new ActivityStackSupervisor(this, mRecentTasks);
    mTaskPersister = new TaskPersister(systemDir, mStackSupervisor, mRecentTasks);

    //3、创建名为"CpuTracker"的线程
    mProcessCpuThread = new Thread("CpuTracker") 
....

�
�该过程共创建了3个线程，分别为“ActivityManager”，“android.ui”，“CpuTracker”。

AMS.start

private void start() {
    Process.removeAllProcessGroups(); //移除所有的进程组
    mProcessCpuThread.start(); //启动CpuTracker线程

    mBatteryStatsService.publish(mContext); //启动电池统计服务
    mAppOpsService.publish(mContext);
    //创建LocalService，并添加到LocalServices
    LocalServices.addService(ActivityManagerInternal.class, new LocalService());
}

LocalService是继承至ActivityManagerInternal(Activity manager local system service interface)

AMS#setSystemProcess

此方法是在SystemServer#startBootstrapServices中触发调用的，主要是各种服务的注册

 public void setSystemProcess() {
        try {
            ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);//注册自己
            ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
            ServiceManager.addService("meminfo", new MemBinder(this));
            ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
            ServiceManager.addService("dbinfo", new DbBinder(this));
....
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
}

mSystemThread#installSystemApplicationInfo调用链：设置包名为”android”的应用信息

1. mSystemThread#installSystemApplicationInfo

2. ContextImpl#installSystemApplicationInfo

3. LoadedApk#installSystemApplicationInfo

/**
     * Sets application info about the system package.
     */
    void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {
        assert info.packageName.equals("android");
        mApplicationInfo = info;
        mClassLoader = classLoader;
    }

SystemServer#startOtherServices