Android Framework学习八：SystemServer及startService原理

SystemServer、SystemServiceManger、SystemService、serviceManager的关系

• 管理机制：SystemServer 通过 SystemServiceManager 管理所有实现了 SystemService 的服务。每个服务初始化后会将自身注册到 ServiceManager，以实现跨进程调用 。
• SystemServer 进程：它是一个包含众多服务的进程，像常见的 AMS（Activity Manager Service，活动管理器服务 ）、PKMS（Package Manager Service，包管理器服务 ）、WMS（Window Manager Service，窗口管理器服务 ）等，大概有 80 多个。
• SystemServiceManager 作用：专门用于管理 SystemServer 中的服务，这些服务基本都实现了 SystemService 类，使得 SystemServiceManager 能够对其进行管理 。
• App 调用方式：当 App 需要调用 systemService 时，在 SystemServer 启动 AMS、WMS、PKMS 等服务时，会将它们添加到 ServiceManager 中，供外部 app 进程调用。ServiceManager 是独立进程，负责管理服务列表。
  

SystemServer进程的执行

frameworks/base/services/java/com/android/server/SystemServer.java

    /*** The main entry point from zygote.*/public static void main(String[] args) {new SystemServer().run();}private void run() {...// Initialize native services.System.loadLibrary("android_servers");...// Initialize the system context.createSystemContext();// Call per-process mainline module initialization.ActivityThread.initializeMainlineModules();// Create the system service manager.mSystemServiceManager = new SystemServiceManager(mSystemContext);...// Start services.try {t.traceBegin("StartServices");startBootstrapServices(t);startCoreServices(t);startOtherServices(t);startApexServices(t);} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {t.traceEnd(); // StartServices}}

包含的Service

startBootstrapServices

    /*** Starts the small tangle of critical services that are needed to get the system off the* ground.  These services have complex mutual dependencies which is why we initialize them all* in one place here.  Unless your service is also entwined in these dependencies, it should be* initialized in one of the other functions.*/private void startBootstrapServices(@NonNull TimingsTraceAndSlog t) {....// FileIntegrityService responds to requests from apps and the system. It needs to run after// the source (i.e. keystore) is ready, and before the apps (or the first customer in the// system) run.mSystemServiceManager.startService(FileIntegrityService.class);// Wait for installd to finish starting up so that it has a chance to// create critical directories such as /data/user with the appropriate// permissions.  We need this to complete before we initialize other services.Installer installer = mSystemServiceManager.startService(Installer.class);// In some cases after launching an app we need to access device identifiers,// therefore register the device identifier policy before the activity manager.mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);// Uri Grants Manager.mSystemServiceManager.startService(UriGrantsManagerService.Lifecycle.class);// Tracks rail data to be used for power statistics.mSystemServiceManager.startService(PowerStatsService.class);...}

startCoreServices

    /*** Starts some essential services that are not tangled up in the bootstrap process.*/private void startCoreServices(@NonNull TimingsTraceAndSlog t) {t.traceBegin("startCoreServices");// Service for system configt.traceBegin("StartSystemConfigService");mSystemServiceManager.startService(SystemConfigService.class);t.traceEnd();t.traceBegin("StartBatteryService");// Tracks the battery level.  Requires LightService.mSystemServiceManager.startService(BatteryService.class);t.traceEnd();// Tracks application usage stats.t.traceBegin("StartUsageService");mSystemServiceManager.startService(UsageStatsService.class);mActivityManagerService.setUsageStatsManager(LocalServices.getService(UsageStatsManagerInternal.class));t.traceEnd();// Tracks whether the updatable WebView is in a ready state and watches for update installs.if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_WEBVIEW)) {t.traceBegin("StartWebViewUpdateService");mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);t.traceEnd();}// Tracks and caches the device state.t.traceBegin("StartCachedDeviceStateService");mSystemServiceManager.startService(CachedDeviceStateService.class);t.traceEnd();// Tracks cpu time spent in binder callst.traceBegin("StartBinderCallsStatsService");mSystemServiceManager.startService(BinderCallsStatsService.LifeCycle.class);t.traceEnd();...}

    /*** Starts a miscellaneous grab bag of stuff that has yet to be refactored and organized.*/private void startOtherServices(@NonNull TimingsTraceAndSlog t) {...ServiceManager.addService("sec_key_att_app_id_provider",new KeyAttestationApplicationIdProviderService(context));t.traceEnd();t.traceBegin("StartKeyChainSystemService");mSystemServiceManager.startService(KeyChainSystemService.class);t.traceEnd();t.traceBegin("StartBinaryTransparencyService");mSystemServiceManager.startService(BinaryTransparencyService.class);t.traceEnd();t.traceBegin("StartSchedulingPolicyService");ServiceManager.addService("scheduling_policy", new SchedulingPolicyService());t.traceEnd();// TelecomLoader hooks into classes with defined HFP logic,// so check for either telephony or microphone.if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_MICROPHONE)|| mPackageManager.hasSystemFeature(PackageManager.FEATURE_TELECOM)|| mPackageManager.hasSystemFeature(PackageManager.FEATURE_TELEPHONY)) {t.traceBegin("StartTelecomLoaderService");mSystemServiceManager.startService(TelecomLoaderService.class);t.traceEnd();}t.traceBegin("StartTelephonyRegistry");telephonyRegistry = new TelephonyRegistry(context, new TelephonyRegistry.ConfigurationProvider());ServiceManager.addService("telephony.registry", telephonyRegistry);t.traceEnd();t.traceBegin("StartEntropyMixer");mEntropyMixer = new EntropyMixer(context);t.traceEnd();mContentResolver = context.getContentResolver();// The AccountManager must come before the ContentServicet.traceBegin("StartAccountManagerService");mSystemServiceManager.startService(ACCOUNT_SERVICE_CLASS);t.traceEnd();...}

安卓13中，手动查询SystemServer中的service数量，如下有183个：

cat frameworks/base/services/java/com/android/server/SystemServer.java | grep startService | wc -l
183

SystemServer启动服务的流程

startService

所有的服务都是通过这个函数启动的

1. getConstructor是调的反射进行service构造
   
2. service创建后，会调用publishBinderService把它注册到serviceManager中
   
3. 通过addService把service添加到sLocalServiceObjects中
   

startService的流程：

startServicer用反射：方便扩展及管理，不然90个service就要实现90种创建的接口。
publishBinderService：注册到serviceManager中，由它统一管理。
addService到LocalServices: 方便Framework层平级的调用。

上层调用service,是通过binder来访问其中功能的，如下图，具体可以参照另外一篇binder的文章

Framework学习系列文章

Android Framework学习一：系统框架、启动过程
Android Framework学习二：Activity创建及View绘制流程
Android Framework学习三：zygote
Android Framework学习四：APP速度优化
Android Framework学习五：APP启动过程原理及速度优化
Android Framework学习六：Binder原理
Android Framework学习七：Handler、Looper、Message
Android Framework学习八：SystemServer及startService原理
作者：帅得不敢出门