SystemServer啓動流程

SystemServer被zygote啓動後會運行到main函數，在這裏面直接運行到run方法

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

在run方法中,會做一些初始化，之後啓動其他服務，最終進入Loop循環

private void run() {
	Looper.prepareMainLooper();
	nativeInit();
	createSystemContext();
	
	mSystemServiceManager = new SystemServiceManager(mSystemContext);
	LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);

	startBootstrapServices();
	startCoreServices();
	startOtherServices();
	
	Looper.loop();
}

nativeInit函數在com_android_server_SystemServer.cpp中，開啓傳感器服務

SensorService::instantiate();

createSystemContext函數創建ActivityThread，並創建mSystemContext

    private void createSystemContext() {
        ActivityThread activityThread = ActivityThread.systemMain();
        mSystemContext = activityThread.getSystemContext();
        mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);
    }

在startBootstrapServices中通過classloader加載類名並調用他們的start方法開啓了一些重要的的系統服務

mActivityManagerService
mPowerManagerService
mDisplayManagerService
mPackageManagerService

在startCoreService中開啓了

LightsService
BatteryService
UsageStatsService
UsageStatsManagerInternal
WebViewUpdateService

在startOtherServices中進行了一大堆初始化，最後運行到初始化UI

// 這裏啓動了launcher
 mActivityManagerService.systemReady()
 
startSystemUi(context)

這裏是發送了一個Intent

static final void startSystemUi(Context context) {
        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.android.systemui",
                    "com.android.systemui.SystemUIService"));
        //Slog.d(TAG, "Starting service: " + intent);
        context.startServiceAsUser(intent, UserHandle.OWNER);
    }

這裏實際是運行到了SystemUIApplication，就是啓動一些系統UI

    private final Class<?>[] SERVICES = new Class[] {
            com.android.systemui.keyguard.KeyguardViewMediator.class,
            com.android.systemui.recent.Recents.class,
            com.android.systemui.volume.VolumeUI.class,
            com.android.systemui.statusbar.SystemBars.class,                 	
            com.android.systemui.usb.StorageNotification.class,
            com.android.systemui.power.PowerUI.class,
            com.android.systemui.media.RingtonePlayer.class
    };