carservice启动流程
大致流程：
- SystemServer启动CarServiceHelperService服务
- 在调用startService后，CarServiceHelperService的onStart方法通过bindService的方式启动CarService（一个系统级别的APK，位于system/priv-app）
- 启动CarService后首先调用onCreate，创建ICarImpl对象并初始化，在此时创建了一系列car相关的核心服务，并遍历init初始化
- 然后调用onBind将该ICarImpl对象返回给CarServiceHelperService，CarServiceHelperService在内部的一个Binder对象ICarServiceHelperImpl传递给CarService，建立双向跨进程
2.6.1. 序列图
2.6.2. 启动CarServiceHelperService服务
frameworks/base/services/java/com/android/server/SystemServer.java - run() —-> startOtherServices()
private static final String CAR_SERVICE_HELPER_SERVICE_CLASS =
"com.android.internal.car.CarServiceHelperService";
......
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
traceBeginAndSlog("StartCarServiceHelperService");
mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS);
traceEnd();
}
—–> frameworks/base/services/core/java/com/android/server/SystemServiceManager.java - startService
@SuppressWarnings("unchecked")
public SystemService startService(String className) {
....
return startService(serviceClass);
}
public <T extends SystemService> T startService(Class<T> serviceClass) {
...
startService(service);
...
}
public void startService(@NonNull final SystemService service) {
......
try {
service.onStart();
...
}
2.6.3. 绑定carservice服务
—–> frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.java - onStart()
//这就是系统中和汽车相关的核心服务CarService，相关源代码在packages/services/Car/service目录下
private static final String CAR_SERVICE_INTERFACE = "android.car.ICar";
@Override
public void onStart() {
Intent intent = new Intent();
intent.setPackage("com.android.car"); //绑定包名，设置广播仅对该包有效
//绑定action，表明想要启动能够响应设置的这个action的活动，并在清单文件AndroidManifest.xml中设置action属性
intent.setAction(CAR_SERVICE_INTERFACE);
//绑定后回调
if (!getContext().bindServiceAsUser(intent, mCarServiceConnection, Context.BIND_AUTO_CREATE,
UserHandle.SYSTEM)) {
Slog.wtf(TAG, "cannot start car service");
}
System.loadLibrary("car-framework-service-jni");
}
- service源码路径：packages/services/Car/service/AndroidManifest.xml
sharedUserId是系统级别的，类似SystemUI，它编译出来同样是一个APK文件
设备文件路径在： /system/priv-app/CarService/CarService.apk
//packages/services/Car/service/AndroidManifest.xml
<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">
......
<application android:label="Car service"
android:directBootAware="true"
android:allowBackup="false"
android:persistent="true">
<service android:name=".CarService"
android:singleUser="true">
<intent-filter>
<action android:name="android.car.ICar" />
</intent-filter>
</service>
<service android:name=".PerUserCarService" android:exported="false" />
</application>
2.6.4. bindService启动流程
context.bindService() ——> onCreate() ——> onBind() ——> Service running ——> onUnbind() ——> onDestroy() ——> Service stop
onBind()将返回给客户端一个IBind接口实例，IBind允许客户端回调服务的方法，比如得到Service的实例、运行状态或其他操作。这个时候把调用者（Context，例如Activity）会和Service绑定在一起，Context退出了，Srevice就会调用onUnbind->onDestroy相应退出。
所以调用bindService的生命周期为：onCreate --> onBind(只一次，不可多次绑定) --> onUnbind --> onDestroy
在Service每一次的开启关闭过程中，只有onStart可被多次调用(通过多次startService调用)，其他onCreate，onBind，onUnbind，onDestroy在一个生命周期中只能被调用一次
2.7. Car Service启动
2.7.1. onCreate
——–> packages/services/Car/service/src/com/android/car/CarService.java - onCreate()
创建ICarImpl实例
@Nullable
private static IVehicle getVehicle() {
try {
//该service启动文件hardware/interfaces/automotive/vehicle/2.0/default/android.hardware.automotive.vehicle@2.0-service.rc
return android.hardware.automotive.vehicle.V2_0.IVehicle.getService();
} ....
return null;
}
@Override
public void onCreate() {
Log.i(CarLog.TAG_SERVICE, "Service onCreate");
//获取hal层的Vehicle service
mVehicle = getVehicle();
//创建ICarImpl实例
mICarImpl = new ICarImpl(this,
mVehicle,
SystemInterface.Builder.defaultSystemInterface(this).build(),
mCanBusErrorNotifier,
mVehicleInterfaceName);
//然后调用ICarImpl的init初始化方法
mICarImpl.init();
//设置boot.car_service_created属性
SystemProperties.set("boot.car_service_created", "1");
linkToDeath(mVehicle, mVehicleDeathRecipient);
//最后将该service注册到ServiceManager
ServiceManager.addService("car_service", mICarImpl);
super.onCreate();
}
//packages/services/Car/service/src/com/android/car/ICarImpl.java
private final VehicleHal mHal;
//构造函数启动一大堆服务
public ICarImpl(Context serviceContext, IVehicle vehicle, SystemInterface systemInterface,
CanBusErrorNotifier errorNotifier, String vehicleInterfaceName) {
mContext = serviceContext;
mSystemInterface = systemInterface;
//创建VehicleHal对象
mHal = new VehicleHal(vehicle);
mVehicleInterfaceName = vehicleInterfaceName;
mSystemActivityMonitoringService = new SystemActivityMonitoringService(serviceContext);
mCarPowerManagementService = new CarPowerManagementService(mContext, mHal.getPowerHal(),
systemInterface);
mCarPropertyService = new CarPropertyService(serviceContext, mHal.getPropertyHal());
.....
//InstrumentClusterService service启动
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);
//注意排序，service存在依赖
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(mCarLocationService);
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);
}
mAllServices = allServices.toArray(new CarServiceBase[allServices.size()]);
}
@MainThread
void init() {
traceBegin("VehicleHal.init");
mHal.init();
traceEnd();
traceBegin("CarService.initAllServices");
//启动的所有服务遍历调用init初始化（各个都继承了CarServiceBase）
for (CarServiceBase service : mAllServices) {
service.init();
}
traceEnd();
}
2.7.2. onBind
将上面onCreate创建的mICarImpl对象返回：
- onBind()回调方法会继续传递通过bindService()传递来的intent对象（即上面的bindServiceAsUser方法）
- onUnbind()会处理传递给unbindService()的intent对象。如果service允许绑定，onBind()会返回客户端与服务互相联系的通信句柄
//packages/services/Car/service/src/com/android/car/CarService.java
@Override
public IBinder onBind(Intent intent) {
return mICarImpl;
}
所以此处的mICarImpl会作为IBinder返回给CarServiceHelperService.java - bindServiceAsUser方法中的参数mCarServiceConnection（回调）
2.7.3. onDestroy
释放mICarImpl创建的资源，包含一系列的服务：
@Override
public void onDestroy() {
Log.i(CarLog.TAG_SERVICE, "Service onDestroy");
mICarImpl.release();
mCanBusErrorNotifier.removeFailureReport(this);
if (mVehicle != null) {
try {
mVehicle.unlinkToDeath(mVehicleDeathRecipient);
mVehicle = null;
} catch (RemoteException e) {
// Ignore errors on shutdown path.
}
}
super.onDestroy();
}
2.8. 回调ServiceConnection
ICarImpl初始化完毕，会作为IBinder返回给CarServiceHelperService.java - bindServiceAsUser方法中绑定此服务的mCarServiceConnection（回调）
mCarServiceConnection初始化如下：
- 其中返回的ICarImpl被保存在了CarServiceHelperService的mCarService
- mCarService.transact跨进程通信，调用ICar.aidl中定义的第一个方法setCarServiceHelper
//frameworks/opt/car/services/src/com/android/internal/car/CarServiceHelperService.java
private static final String CAR_SERVICE_INTERFACE = "android.car.ICar";
private IBinder mCarService;
private final ICarServiceHelperImpl mHelper = new ICarServiceHelperImpl();
private final ServiceConnection mCarServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
Slog.i(TAG, "**CarService connected**");
//1. 返回的ICarImpl被保存在了CarServiceHelperService的mCarService
mCarService = iBinder;
// Cannot depend on ICar which is defined in CarService, so handle binder call directly
// instead.
// void setCarServiceHelper(in IBinder helper)
Parcel data = Parcel.obtain();
data.writeInterfaceToken(CAR_SERVICE_INTERFACE);
//将ICarServiceHelperImpl类型的对象作为数据跨进程传递
data.writeStrongBinder(mHelper.asBinder());
try {
//2.跨进程传输
//对端是mCarService即ICarImpl，调用binder的transact进行跨进程通信
//其code代表需要调用的对端方法，data为携带的传输数据
//FIRST_CALL_TRANSACTION = 0x00000001，即调用对端ICar.aidl中定义的第一个方法setCarServiceHelper
mCarService.transact(IBinder.FIRST_CALL_TRANSACTION, // setCarServiceHelper
data, null, Binder.FLAG_ONEWAY);
} catch (RemoteException e) {
Slog.w(TAG, "RemoteException from car service", e);
handleCarServiceCrash();
}
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
handleCarServiceCrash();
}
};
2.9. 跨进程setCarServiceHelper
@Override
public void setCarServiceHelper(IBinder helper) {
int uid = Binder.getCallingUid();
if (uid != Process.SYSTEM_UID) {
throw new SecurityException("Only allowed from system");
}
synchronized (this) {
//将ICarServiceHelper的代理端保存在ICarImpl内部mICarServiceHelper
mICarServiceHelper = ICarServiceHelper.Stub.asInterface(helper);
//同时也传给了SystemInterface
//此时他们有能力跨进程访问CarServiceHelperService
mSystemInterface.setCarServiceHelper(mICarServiceHelper);
}
}
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最后
启动流程图
