CarService 中運行邏輯

CarService 中運行邏輯

在Android O中，Google在原有的Framework架構中引入了Android Car的功能結構，這裏着重對Android Service模塊進行相關的講解。由於Car模塊 Android O和P延續統一體系，這裏就按照P的源碼，O/P架構進行解析。Car的相關架構，請參照Android Automotive架構，不再做多的贅述、

Car service

CarService集中在一個App中。這個App需要非常高的權限，所以這是一個系統App。其Manifest開頭如下：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:androidprv="http://schemas.android.com/apk/prv/res/android"
        package="com.android.car"
        coreApp="true"
        android:sharedUserId="android.uid.system">

android:sharedUserId屬性使得這個應用具有系統權限。

CarService.java的onCreate()方法會new一個ICarImpl，並對一系列的服務進行初始化。
CarService並非一個服務，而是一系列的服務。這些服務都在ICarImpl.java構造函數中列了出來。

首先是CarService中onCreate()中關鍵代碼：

 mICarImpl = new ICarImpl(this,
                mVehicle,
                SystemInterface.Builder.defaultSystemInterface(this).build(),
                mCanBusErrorNotifier,
                mVehicleInterfaceName);
        mICarImpl.init();

再者是ICarImpl類中的構造函數：

 public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,
            CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {
        mContext = serviceContext;
        mSystemInterface = systemInterface;
        mHal = new VehicleHal(vehicle);
        mVehicleInterfaceName = vehicleInterfaceName;
        mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);
        mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),
                systemInterface);
        mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());
        mCarDrivingStateService = new CarDrivingStateService(serviceContext, mCarPropertyService);
        mCarUXRestrictionsService = new CarUxRestrictionsManagerService(serviceContext,
                mCarDrivingStateService, mCarPropertyService);
        mCarPackageManagerService = new CarPackageManagerService(serviceContext,
                mCarUXRestrictionsService,
                mSystemActivityMonitoringService);
        mCarInputService = new CarInputService(serviceContext, mHal.getInputHal());
        mCarProjectionService = new CarProjectionService(serviceContext, mCarInputService);
        mGarageModeService = new GarageModeService(mContext, mCarPowerManagementService);
        mAppFocusService = new AppFocusService(serviceContext, mSystemActivityMonitoringService);
        mCarAudioService = new CarAudioService(serviceContext);
        mCarNightService = new CarNightService(serviceContext, mCarPropertyService);
        mInstrumentClusterService = new InstrumentClusterService(serviceContext,
                mAppFocusService, mCarInputService);
        mSystemStateControllerService = new SystemStateControllerService(serviceContext,
                mCarPowerManagementService, mCarAudioService, this);
        mPerUserCarServiceHelper = new PerUserCarServiceHelper(serviceContext);
        mCarBluetoothService = new CarBluetoothService(serviceContext, mCarPropertyService,
                mPerUserCarServiceHelper, mCarUXRestrictionsService);
        mVmsSubscriberService = new VmsSubscriberService(serviceContext, mHal.getVmsHal());
        mVmsPublisherService = new VmsPublisherService(serviceContext, mHal.getVmsHal());
        mCarDiagnosticService = new CarDiagnosticService(serviceContext, mHal.getDiagnosticHal());
        mCarStorageMonitoringService = new CarStorageMonitoringService(serviceContext,
                systemInterface);
        mCarConfigurationService =
                new CarConfigurationService(serviceContext, new JsonReaderImpl());
        mUserManagerHelper = new CarUserManagerHelper(serviceContext);
        mCarLocationService = new CarLocationService(mContext, mCarPowerManagementService,
                mCarPropertyService, mUserManagerHelper);

        // Be careful with order. Service depending on other service should be inited later.
        List<CarServiceBase> allServices = new ArrayList<>();
        allServices.add(mSystemActivityMonitoringService);
        allServices.add(mCarPowerManagementService);
        allServices.add(mCarPropertyService);
        allServices.add(mCarDrivingStateService);
        allServices.add(mCarUXRestrictionsService);
        allServices.add(mCarPackageManagerService);
        allServices.add(mCarInputService);
        allServices.add(mGarageModeService);
        allServices.add(mAppFocusService);
        allServices.add(mCarAudioService);
        allServices.add(mCarNightService);
        allServices.add(mInstrumentClusterService);
        allServices.add(mCarProjectionService);
        allServices.add(mSystemStateControllerService);
        allServices.add(mCarBluetoothService);
        allServices.add(mCarDiagnosticService);
        allServices.add(mPerUserCarServiceHelper);
        allServices.add(mCarStorageMonitoringService);
        allServices.add(mCarConfigurationService);
        allServices.add(mVmsSubscriberService);
        allServices.add(mVmsPublisherService);

        if (mUserManagerHelper.isHeadlessSystemUser()) {
            mCarUserService = new CarUserService(serviceContext, mUserManagerHelper);
            allServices.add(mCarUserService);
        }

        allServices.add(mCarLocationService);
        mAllServices = allServices.toArray(new CarServiceBase[allServices.size()]);
    }

再是ICarImpl中init()方法：

 void init() {
        traceBegin("VehicleHal.init");
        mHal.init();
        traceEnd();
        traceBegin("CarService.initAllServices");
        for (CarServiceBase service : mAllServices) {
            service.init();
        }
        traceEnd();
    }

閱讀源碼會發現，CarService的onCreate()方法new完一個ICarImpl對象會執行mICarImpl.init()方法初始化。

首先對VehicleHal執行了init()，先是調用HalClient.getAllPropConfigs()從Vehicle HAL獲取所有的屬性，然後對各個service.takeSupportedProperties(properties)獲取CarService支持的屬性。

接着又對各個繼承了CarServiceBase的Service執行service.init()方法。
比如PropertyHalServiceBase繼承了CarServiceBase，在init()方法裏面對各個屬性執行了mVehicleHal.subscribeProperty(this, prop)，然後調用了VehicleHal.java的subscribeProperty(HalServiceBase service, int property)，接着調用HalClient.subscribe(SubscribeOptions… options)，這樣就把所有屬性都subscribe了，這樣CarService就能接收到Vehicle HAL發上來的所有屬性變化。