Android10 启动之SystemServer源码分析

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

 private void run() {
        try {
           ...
            //准备主线程lopper
            android.os.Process.setThreadPriority(
                    android.os.Process.THREAD_PRIORITY_FOREGROUND);
            android.os.Process.setCanSelfBackground(false);
            Looper.prepareMainLooper();
            Looper.getMainLooper().setSlowLogThresholdMs(
                    SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
            // 加载libandroid_servers.so库
            System.loadLibrary("android_servers");
           //检测上次关机过程是否失败，这个调用可能不会返回
            performPendingShutdown();
             //初始化系统上下文
            createSystemContext();
           //创建系统服务管理者--SystemServiceManager
            mSystemServiceManager = new SystemServiceManager(mSystemContext);
            mSystemServiceManager.setStartInfo(mRuntimeRestart,
                    mRuntimeStartElapsedTime, mRuntimeStartUptime);
             //将mSystemServiceManager添加到本地服务中，至于什么是LocalServices，它有什么作用，
             //以后再单独开一篇文章来讲解
            LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
            //为可以并行化的init任务准备线程池
            SystemServerInitThreadPool.get();
        } finally {
            traceEnd();  // InitBeforeStartServices
        }
        // 在这里开始启动一系列服务了
        try {
            traceBeginAndSlog("StartServices");
            // 启动引导服务
            startBootstrapServices();
            // 启动核心服务
            startCoreServices();
            // 启动其他服务
            startOtherServices();
            //停止init线程池
            SystemServerInitThreadPool.shutdown();
        } catch (Throwable ex) {
            Slog.e("System", "******************************************");
            Slog.e("System", "************ Failure starting system services", ex);
            throw ex;
        } finally {
            traceEnd();
        }
        ...
        // 死循环执行
        Looper.loop();
        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

private void createSystemContext() {
    //创建system_server进程的上下文信息
    ActivityThread activityThread = ActivityThread.systemMain();
    mSystemContext = activityThread.getSystemContext();
    //设置主题
    mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
    //获取systemui上下文信息，并设置主题
    final Context systemUiContext = activityThread.getSystemUiContext();
    systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
}

 private void startBootstrapServices() {
        // 尽早启动看门狗，这样我们在早期启动陷入死锁时就可以使system server崩溃重启。
        final Watchdog watchdog = Watchdog.getInstance();
        watchdog.start();
        //启动Installer Service，这个Service 通过binder与installd进程通讯，负责apk安装相关的工作
        Installer installer = mSystemServiceManager.startService(Installer.class);
        //设备标识符策略服务
        mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
        // 管理uri授权
        mSystemServiceManager.startService(UriGrantsManagerService.Lifecycle.class);
        //启动ActivityTaskManagerService和ActivityManagerService
        ActivityTaskManagerService atm = mSystemServiceManager.startService(
                ActivityTaskManagerService.Lifecycle.class).getService();
        mActivityManagerService = ActivityManagerService.Lifecycle.startService(
                mSystemServiceManager, atm);
        mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
        mActivityManagerService.setInstaller(installer);
        mWindowManagerGlobalLock = atm.getGlobalLock();
        //电源管理器需要尽早启动，因为其他服务需要它。
        mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
        //启动热缓解服务，目的是在手机开始过热时进行有效的热缓解
        mSystemServiceManager.startService(ThermalManagerService.class);
        // Now that the power manager has been started, let the activity manager
        // initialize power management features.
        mActivityManagerService.initPowerManagement();
        //启动系统恢复服务，负责协调设备上与恢复有关的功能。
        mSystemServiceManager.startService(RecoverySystemService.class);
        //到这里为止，系统启动的必须服务已经加载完毕
        RescueParty.noteBoot(mSystemContext);
        //管理LED和屏幕背光，我们需要它来显示
        mSystemServiceManager.startService(LightsService.class);
        //管理显示设备
        //在package manager 启动之前，需要启动display manager 提供display metrics
        mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
     //只有DisplayManagerService会对PHASE_WAIT_FOR_DEFAULT_DISPLAY做处理
     //目的是在初始化包管理器之前，首先需要获取一个默认的显示设备
     mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
        // 启动 package manager.
        if (!mRuntimeRestart) {
            MetricsLogger.histogram(null, "boot_package_manager_init_start",
                    (int) SystemClock.elapsedRealtime());
        }
        try {
            Watchdog.getInstance().pauseWatchingCurrentThread("packagemanagermain");
            mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
                    mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
        } finally {
            Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");
        }
        mFirstBoot = mPackageManagerService.isFirstBoot();
        mPackageManager = mSystemContext.getPackageManager();
        //启动UserManager Service
        mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
       //为系统进程设置应用程序实例并启动
        mActivityManagerService.setSystemProcess();
        //使用ActivityManager实例完成看门狗设置并监听是否重启
        watchdog.init(mSystemContext, mActivityManagerService);
        // DisplayManagerService needs to setup android.display scheduling related policies
        // since setSystemProcess() would have overridden policies due to setProcessGroup
        mDisplayManagerService.setupSchedulerPolicies();
        //负责动态资源overlay
        mSystemServiceManager.startService(new OverlayManagerService(mSystemContext, installer));
        mSystemServiceManager.startService(new SensorPrivacyService(mSystemContext));
        if (SystemProperties.getInt("persist.sys.displayinset.top", 0) > 0) {
            // DisplayManager needs the overlay immediately.
            mActivityManagerService.updateSystemUiContext();
            LocalServices.getService(DisplayManagerInternal.class).onOverlayChanged();
        }
          //传感器服务需要访问包管理器服务、app ops服务和权限服务，
         //因此我们在它们之后启动它。
         //在单独的线程中启动传感器服务。在使用它之前应该检查完成情况。
        mSensorServiceStart = SystemServerInitThreadPool.get().submit(() -> {
            TimingsTraceLog traceLog = new TimingsTraceLog(
                    SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);
            traceLog.traceBegin(START_SENSOR_SERVICE);
            startSensorService();
            traceLog.traceEnd();
        }, START_SENSOR_SERVICE);
    }

 private void startCoreServices() {
        // 追踪电池充电状态和电量。需要LightService
        mSystemServiceManager.startService(BatteryService.class);
         //跟踪应用程序使用状态
        mSystemServiceManager.startService(UsageStatsService.class);
        mActivityManagerService.setUsageStatsManager(
                LocalServices.getService(UsageStatsManagerInternal.class));
        // 跟踪可更新的WebView是否处于就绪状态，并监视更新安装。
        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_WEBVIEW)) {
            traceBeginAndSlog("StartWebViewUpdateService");
            mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
            traceEnd();
        }
       //跟踪并缓存设备状态。
        mSystemServiceManager.startService(CachedDeviceStateService.class);
        // 跟踪在Binder调用中花费的cpu时间
        mSystemServiceManager.startService(BinderCallsStatsService.LifeCycle.class);
        // 跟踪handlers中处理messages所花费的时间。
        mSystemServiceManager.startService(LooperStatsService.Lifecycle.class);
        //管理apk回滚
        mSystemServiceManager.startService(RollbackManagerService.class);
        // 用于捕获bugreport,adb bugreport 命令调用的就是这个服务
        mSystemServiceManager.startService(BugreportManagerService.class);
        // 管理Gpu和Gpu驱动的服务
        mSystemServiceManager.startService(GpuService.class);
    }

 mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");

Intent getHomeIntent() {
        Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
        intent.setComponent(mTopComponent);
        intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
        if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
            intent.addCategory(Intent.CATEGORY_HOME);
        }
        return intent;
    }