Android 系统服务TelecomService启动过程原理分析

 更新时间:2020年07月22日 11:32:28   作者:Jason_Wang  
这篇文章主要介绍了Android 系统服务TelecomService启动过程原理分析,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友们下面随着小编来一起学习学习吧

由于一直负责的是Android Telephony部分的开发工作,对于通信过程的上层部分Telecom服务以及UI都没有认真研究过。最近恰好碰到一个通话方面的问题,涉及到了Telecom部分,因而就花时间仔细研究了下相关的代码。这里做一个简单的总结。这篇文章,主要以下两个部分的内容:

  • 什么是Telecom服务?其作用是什么?
  • Telecom模块的启动与初始化过程;

接下来一篇文章,主要以实际通话过程为例,分析下telephony收到来电后如何将电话信息发送到Telecom模块以及Telecom是如何处理来电。

什么是Telecom服务

Telecom是Android的一个系统服务,其主要作用是管理Android系统当前的通话,如来电显示,接听电话,挂断电话等功能,在Telephony模块与上层UI之间起到了一个桥梁的作用。比如,Telephony有接收到新的来电时,首先会告知Telecom,然后由Telecom服务通知上层应用来电信息,并显示来电界面。

Telecom服务对外提供了一个接口类TelecomManager,通过其提供的接口,客户端可以查询通话状态,发送通话请求以及添加通话链接等。

从Telecom进程对应的AndroidManifest.xml文件来看,Telecom进程的用户ID跟系统进程用户ID相同,是系统的核心服务。那么,其中android:process="system"这个属性值表示什么意思了?查看官方文档,这个表示Telecom将启动在进程system中,这样可以跟其他进程进行资源共享了(对于Android这个全局进程,就是SystemServer所在的进程)。

android:process

By setting this attribute to a process name that's shared with another application, you can arrange for components of both applications to run in the same process — but only if the two applications also share a user ID and be signed with the same certificate.

If the name assigned to this attribute begins with a colon (‘:'), a new process, private to the application, is created when it's needed. If the process name begins with a lowercase character, a global process of that name is created. A global process can be shared with other applications, reducing resource usage.

 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:androidprv="http://schemas.android.com/apk/prv/res/android"
   package="com.android.server.telecom"
   android:versionCode="1"
   android:versionName="1.0.0"
   coreApp="true"
   android:sharedUserId="android.uid.system">

   <application android:label="@string/telecommAppLabel"
    android:icon="@mipmap/ic_launcher_phone"
    android:allowBackup="false"
    android:supportsRtl="true"
    android:process="system"
    android:usesCleartextTraffic="false"
    android:defaultToDeviceProtectedStorage="true"
    android:directBootAware="true">
   ....
   // 包含TelecomService
   <service android:name=".components.TelecomService"
     android:singleUser="true"
     android:process="system">
    <intent-filter>
     <action android:name="android.telecom.ITelecomService" />
    </intent-filter>
   </service>
  ....
  </application>
 </manifest>

代码路径:

/android/applications/sources/services/Telecomm/
/android/frameworks/base/telecomm/

了解了什么是Telecom服务之后,就来看一看Telecom服务是如何启动与初始化的。

Telecom进程的启动与初始化

在SystemServer进程初始化完成启动完系统的核心服务如ActivityManagerService后,就会加载系统其它服务,这其中就包含了一个与Telecom服务启动相关的系统服务专门用于加载Telecom:

 private void startOtherServices() {
  ....
  //启动TelecomLoaderService系统服务,用于加载Telecom
  mSystemServiceManager.startService(TelecomLoaderService.class);
  // 启动telephony注册服务,用于注册监听telephony状态的接口
  telephonyRegistry = new TelephonyRegistry(context);
  ServiceManager.addService("telephony.registry", telephonyRegistry);
 }

调用系统服务管家SystemServiceManager的接口startService创建新的服务,并注册到系统中,最后调用onStart()启动服务。

 public class SystemServiceManager {

  @SuppressWarnings("unchecked")
  public SystemService startService(String className) {
   final Class<SystemService> serviceClass;
   try {
    serviceClass = (Class<SystemService>)Class.forName(className);
   } catch (ClassNotFoundException ex) {
    ....
   }
   return startService(serviceClass);
  }

  // 服务的class文件来创建新的服务对象(服务必须继承SystemService)
  @SuppressWarnings("unchecked")
  public <T extends SystemService> T startService(Class<T> serviceClass) {
   try {
    final String name = serviceClass.getName();
    Slog.i(TAG, "Starting " + name);
    Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name);

    // Create the service.
    if (!SystemService.class.isAssignableFrom(serviceClass)) {
     throw new RuntimeException("Failed to create " + name
       + ": service must extend " + SystemService.class.getName());
    }
    final T service;
    try {
     Constructor<T> constructor = serviceClass.getConstructor(Context.class);
     service = constructor.newInstance(mContext);
    } catch (InstantiationException ex) {
     throw new RuntimeException("Failed to create service " + name
       + ": service could not be instantiated", ex);
    } 
    ....
    // Register it.
    mServices.add(service);

    // Start it.
    try {
     service.onStart();
    } catch (RuntimeException ex) {
     throw new RuntimeException("Failed to start service " + name
       + ": onStart threw an exception", ex);
    }
    return service;
   } finally {
    Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
   }
  }
 }

创建TelecomLoaderService系统服务,将系统默认的SMS应用,拨号应用以及SIM通话管理应用(不知道这个什么鬼)告知PackageManagerService(PMS),以便在适当的时候可以找到应用。

 public class TelecomLoaderService extends SystemService {
  ...
  public TelecomLoaderService(Context context) {
   super(context);
   mContext = context;
   registerDefaultAppProviders();
  }

  @Override
  public void onStart() {
  }

  private void registerDefaultAppProviders() {
   final PackageManagerInternal packageManagerInternal = LocalServices.getService(
     PackageManagerInternal.class);

   // Set a callback for the package manager to query the default sms app.
   packageManagerInternal.setSmsAppPackagesProvider(
     new PackageManagerInternal.PackagesProvider() {
    @Override
    public String[] getPackages(int userId) {
     synchronized (mLock) {
     ....
     ComponentName smsComponent = SmsApplication.getDefaultSmsApplication(
       mContext, true);
     if (smsComponent != null) {
      return new String[]{smsComponent.getPackageName()};
     }
     return null;
    }
   });

   // Set a callback for the package manager to query the default dialer app.
   packageManagerInternal.setDialerAppPackagesProvider(
     new PackageManagerInternal.PackagesProvider() {
    @Override
    public String[] getPackages(int userId) {
     synchronized (mLock) {
     ....
     String packageName = DefaultDialerManager.getDefaultDialerApplication(mContext);
     if (packageName != null) {
      return new String[]{packageName};
     }
     return null;
    }
   });

   // Set a callback for the package manager to query the default sim call manager.
   packageManagerInternal.setSimCallManagerPackagesProvider(
     new PackageManagerInternal.PackagesProvider() {
    @Override
    public String[] getPackages(int userId) {
     synchronized (mLock) {
     ....
     TelecomManager telecomManager =
      (TelecomManager) mContext.getSystemService(Context.TELECOM_SERVICE);
     PhoneAccountHandle phoneAccount = telecomManager.getSimCallManager(userId);
     if (phoneAccount != null) {
      return new String[]{phoneAccount.getComponentName().getPackageName()};
     }
     return null;
    }
   });
  }
 }

到目前,好像Telecom服务并没启动,那么究竟Telecom服务在哪里启动的了?仔细看TelecomLoaderService的源代码,其中有一个onBootPhase的函数,用于SystemServer告知系统服务目前系统启动所处的阶段。这里可以看到,等(ActivityManagerService)AMS启动完成以后,就可以开始连接Telecom服务了:

  • 首先,注册默认应用(SMS/Dialer etc)通知对象,以便这些应用发送变更(如下载了一个第三方的SMS应用时,可以通知系统这一变化);
  • 接着,注册运营商配置变化的广播接收器,如果配置有变化时,系统会收到通知;
  • 绑定TelecomService,并将其注册到系统中。
 public class TelecomLoaderService extends SystemService {

  private static final ComponentName SERVICE_COMPONENT = new ComponentName(
    "com.android.server.telecom",
    "com.android.server.telecom.components.TelecomService");

  private static final String SERVICE_ACTION = "com.android.ITelecomService";

  // 当前系统启动的阶段
  @Override
  public void onBootPhase(int phase) {
   if (phase == PHASE_ACTIVITY_MANAGER_READY) {
    registerDefaultAppNotifier();
    registerCarrierConfigChangedReceiver();
    connectToTelecom();
   }
  }

  //绑定Telecom服务
  private void connectToTelecom() {
   synchronized (mLock) {
    if (mServiceConnection != null) {
     // TODO: Is unbinding worth doing or wait for system to rebind?
     mContext.unbindService(mServiceConnection);
     mServiceConnection = null;
    }

    TelecomServiceConnection serviceConnection = new TelecomServiceConnection();
    Intent intent = new Intent(SERVICE_ACTION);
    intent.setComponent(SERVICE_COMPONENT);
    int flags = Context.BIND_IMPORTANT | Context.BIND_FOREGROUND_SERVICE
      | Context.BIND_AUTO_CREATE;

    // Bind to Telecom and register the service
    if (mContext.bindServiceAsUser(intent, serviceConnection, flags, UserHandle.SYSTEM)) {
     mServiceConnection = serviceConnection;
    }
   }
  }
 }

服务绑定:https://developer.android.com/guide/components/bound-services.html

将服务添加到ServiceManager中,如果Telecom服务连接中断时,则重新连接:

 public class TelecomLoaderService extends SystemService {

  private class TelecomServiceConnection implements ServiceConnection {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
     // Normally, we would listen for death here, but since telecom runs in the same process
     // as this loader (process="system") thats redundant here.
     try {
      service.linkToDeath(new IBinder.DeathRecipient() {
       @Override
       public void binderDied() {
        connectToTelecom();
       }
      }, 0);
      SmsApplication.getDefaultMmsApplication(mContext, false);
      //添加Telecom服务
      ServiceManager.addService(Context.TELECOM_SERVICE, service);
      ....
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {
     connectToTelecom();
    }
   }
 }

绑定服务时,调用TelecomService的onBind接口,对整个Telecom系统进行初始化,并返回一个IBinder接口:

 /**
  * Implementation of the ITelecom interface.
  */
 public class TelecomService extends Service implements TelecomSystem.Component {

  @Override
  public IBinder onBind(Intent intent) {
   // 初始化整个Telecom系统
   initializeTelecomSystem(this);
   //返回IBinder接口
   synchronized (getTelecomSystem().getLock()) {
    return getTelecomSystem().getTelecomServiceImpl().getBinder();
   }
  }

 }

Telecom系统初始化,主要工作是新建一个TelecomSystem的类,在这个类中,会对整个Telecom服务的相关类都初始化:

 static void initializeTelecomSystem(Context context) {
   if (TelecomSystem.getInstance() == null) {

    final NotificationManager notificationManager =
      (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    // 用于获取联系人
    contactInfoHelper = new ContactInfoHelper(context);
    // 新建一个单例模式的对象
    TelecomSystem.setInstance(new TelecomSystem(....));
   }
   ....
  }
 }

构造一个单例TelecomSystem对象:

 public TelecomSystem(
    Context context,
    /* 用户未接来电通知类(不包括已接或者拒绝的电话) */
    MissedCallNotifierImplFactory missedCallNotifierImplFactory,
    /* 查询来电信息 */
    CallerInfoAsyncQueryFactory callerInfoAsyncQueryFactory,
    /* 耳机接入状态监听 */
    HeadsetMediaButtonFactory headsetMediaButtonFactory,
    /* 距离传感器管理 */
    ProximitySensorManagerFactory proximitySensorManagerFactory,
    /* 通话时电话管理 */
    InCallWakeLockControllerFactory inCallWakeLockControllerFactory,
    /* 音频服务管理 */
    AudioServiceFactory audioServiceFactory,
    /* 蓝牙设备管理 */
    BluetoothPhoneServiceImplFactory bluetoothPhoneServiceImplFactory,
    BluetoothVoIPServiceImplFactory bluetoothVoIPServiceImplFactory,
    /* 查询所有超时信息 */
    Timeouts.Adapter timeoutsAdapter,
    /* 响铃播放 */
    AsyncRingtonePlayer asyncRingtonePlayer,
    /* 电话号码帮助类 */
    PhoneNumberUtilsAdapter phoneNumberUtilsAdapter,
    /* 通话时阻断通知 */
    InterruptionFilterProxy interruptionFilterProxy) {
   mContext = context.getApplicationContext();
   // 初始化telecom相关的feature
   TelecomFeature.makeFeature(mContext);
   // 初始化telecom的数据库
   TelecomSystemDB.initialize(mContext);
   // 创建一个PhoneAccount注册管理类
   mPhoneAccountRegistrar = new PhoneAccountRegistrar(mContext);
   ....
   // 初始化通话管家,正是它负责与上层UI的交互
   mCallsManager = new CallsManager(
     mContext, mLock, mContactsAsyncHelper,
     callerInfoAsyncQueryFactory, mMissedCallNotifier,
     mPhoneAccountRegistrar, headsetMediaButtonFactory,
     proximitySensorManagerFactory, inCallWakeLockControllerFactory,
     audioServiceFactory, bluetoothManager,
     wiredHeadsetManager, systemStateProvider,
     defaultDialerAdapter, timeoutsAdapter,AsyncRingtonePlayer,
     phoneNumberUtilsAdapter, interruptionFilterProxy);

   CallsManager.initialize(mCallsManager);
   // 注册需要接收的广播 
   mContext.registerReceiver(mUserSwitchedReceiver, USER_SWITCHED_FILTER);
   mContext.registerReceiver(mUserStartingReceiver, USER_STARTING_FILTER);
   mContext.registerReceiver(mFeatureChangedReceiver, FEATURE_CHANGED_FILTER);
   mContext.registerReceiver(mEmergencyReceiver, EMERGENCY_STATE_CHANGED);
   .... 
   // 所有来电与去电的处理中转站
   mCallIntentProcessor = new CallIntentProcessor(mContext, mCallsManager);
   // 创建一个TelecomServiceImpl用于调用TelecomService的接口
   mTelecomServiceImpl = new TelecomServiceImpl(
     mContext, mCallsManager, mPhoneAccountRegistrar,
     new CallIntentProcessor.AdapterImpl(),
     new UserCallIntentProcessorFactory() {
      @Override
      public UserCallIntentProcessor create(Context context, UserHandle userHandle) {
       return new UserCallIntentProcessor(context, userHandle);
      }
     },
     defaultDialerAdapter,
     new TelecomServiceImpl.SubscriptionManagerAdapterImpl(),
     mLock);
   // 执行特定的初始化操作
   initialize(mContext);
  }
 }

Android Telephony中的PhoneAccount到底起到个什么作用了?按照源码中的说明来理解,PhoneAccount表示了不同的接听或者拨打电话的方式,比如用户可以通过SIM卡来拨打电话,也可以拨打视频电话,抑或一个紧急通话,甚至可以通过telephony内部的接口来实现拨号,而Android正是通过PhoneAccount来区分这几种通话方式的。与之相对应的一个类PhoneAccountHandle则是用于表示哪一个用户正在使用通话服务。

至此整个Telecom服务就启动完成了,这样Telecom服务就可以处理来电或者去电了。在接下来的一篇文章里,将分析下来电是如何在Telecom中传递与处理,然后发送到上层UI界面的。

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