Android 系统服务TelecomService启动过程分析

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。

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

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 serviceClass;
            try {
                serviceClass = (Class)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 startService(Class 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 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TelecomServiceonBind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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