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Android 系统服务TelecomService启动过程原理分析

程序员文章站 2022-07-04 17:09:31
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...

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:

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。