SystemServer是由zygote启动的启动后会先走main方法看注释也可以看到此方法是The main entry point from zygote.接着往下走就到了run方法frameworks/base/services/java/com/android/server/SystemServer.javapublic static void main(String[] args) { new SystemServer().run(); } private void run() { ... Looper.prepareMainLooper(); Looper.getMainLooper().setSlowLogThresholdMs( SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS); // Start services. try { t.traceBegin(StartServices); startBootstrapServices(t); startCoreServices(t); startOtherServices(t); } catch (Throwable ex) { Slog.e(System, ******************************************); Slog.e(System, ************ Failure starting system services, ex); throw ex; } finally { t.traceEnd(); // StartServices } ... // Loop forever. Looper.loop(); throw new RuntimeException(Main thread loop unexpectedly exited); }然后走startBootstrapServices这里主要是启动一些系统的关键服务这些服务具有复杂的相互依赖关系。/** * 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) { t.traceBegin(startBootstrapServices); ... // Activity manager runs the show. t.traceBegin(StartActivityManager); // TODO: Might need to move after migration to WM. ActivityTaskManagerService atm mSystemServiceManager.startService( ActivityTaskManagerService.Lifecycle.class).getService(); mActivityManagerService ActivityManagerService.Lifecycle.startService( mSystemServiceManager, atm); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); mWindowManagerGlobalLock atm.getGlobalLock(); t.traceEnd(); ... // Set up the Application instance for the system process and get started. t.traceBegin(SetSystemProcess); mActivityManagerService.setSystemProcess(); t.traceEnd(); ... t.traceBegin(StartPackageManagerService); try { Watchdog.getInstance().pauseWatchingCurrentThread(packagemanagermain); mPackageManagerService PackageManagerService.main(mSystemContext, installer, domainVerificationService, mFactoryTestMode ! FactoryTest.FACTORY_TEST_OFF, mOnlyCore); } finally { Watchdog.getInstance().resumeWatchingCurrentThread(packagemanagermain); } }然后走startCoreServices方法这个方法主要是启动一些在开机过程中没有互相依赖的基本服务。/** * 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 config t.traceBegin(StartSystemConfigService); mSystemServiceManager.startService(SystemConfigService.class); t.traceEnd(); t.traceBegin(StartBatteryService); // Tracks the battery level. Requires LightService. mSystemServiceManager.startService(BatteryService.class); t.traceEnd(); ... // Service for GPU and GPU driver. t.traceBegin(GpuService); mSystemServiceManager.startService(GpuService.class); t.traceEnd(); // Handles system process requests for remotely provisioned keys data. t.traceBegin(StartRemoteProvisioningService); mSystemServiceManager.startService(RemoteProvisioningService.class); t.traceEnd(); // TODO(b/277600174): Start CpuMonitorService on all builds and not just on debuggable // builds once the Android JobScheduler starts using this service. if (Build.IS_DEBUGGABLE || Build.IS_ENG) { // Service for CPU monitor. t.traceBegin(CpuMonitorService); mSystemServiceManager.startService(CpuMonitorService.class); t.traceEnd(); } t.traceEnd(); // startCoreServices }然后走startOtherServices方法此方法中主要是启动一些系统中其他的服务/** * Starts a miscellaneous grab bag of stuff that has yet to be refactored and organized. */ private void startOtherServices(NonNull TimingsTraceAndSlog t) { t.traceBegin(startOtherServices); final Context context mSystemContext; DynamicSystemService dynamicSystem null; IStorageManager storageManager null; NetworkManagementService networkManagement null; IpSecService ipSecService null; VpnManagerService vpnManager null; VcnManagementService vcnManagement null; NetworkStatsService networkStats null; NetworkPolicyManagerService networkPolicy null; NsdService serviceDiscovery null; WindowManagerService wm null; SerialService serial null; NetworkTimeUpdateService networkTimeUpdater null; InputManagerService inputManager null; TelephonyRegistry telephonyRegistry null; ConsumerIrService consumerIr null; MmsServiceBroker mmsService null; HardwarePropertiesManagerService hardwarePropertiesService null; PacProxyService pacProxyService null; ... t.traceBegin(StartVibratorManagerService); mSystemServiceManager.startService(VibratorManagerService.Lifecycle.class); t.traceEnd(); t.traceBegin(StartDynamicSystemService); dynamicSystem new DynamicSystemService(context); ServiceManager.addService(dynamic_system, dynamicSystem); t.traceEnd(); if (!isWatch) { t.traceBegin(StartConsumerIrService); consumerIr new ConsumerIrService(context); ServiceManager.addService(Context.CONSUMER_IR_SERVICE, consumerIr); t.traceEnd(); } t.traceBegin(StartAlarmManagerService); mSystemServiceManager.startService(ALARM_MANAGER_SERVICE_CLASS); t.traceEnd(); t.traceBegin(StartInputManagerService); inputManager new InputManagerService(context); t.traceEnd(); ... }以下是一个在systemserver中启动AMS的流程且WindowManagerService以及ActivityManagerService等的服务的进程号都是SystemServer但是是跑在不同的线程上