Android源码(2) --- SystemServer进程启动流程

SystemServer 进程

1.1 SystemServer进程是由Zygote进程fork 出来的。上篇介绍了fork过程1.2 SystemServer进程 是用来启动各种系统服务的进程，例如ActivityManagerService,WindowManagerService,PowerManagerService，PackageManagerService等等，当应用需要系统服务也是通过SystemServer进程通讯获取服务对象进行交互。

SystemServer 调用

初始化 /** * The main entry point from zygote. */ public static void main(String[] args) { new SystemServer().run(); } private void run() { // If a device's clock is before 1970 (before 0), a lot of // APIs crash dealing with negative numbers, notably // java.io.File#setLastModified, so instead we fake it and // hope that time from cell towers or NTP fixes it shortly. if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) { Slog.w(TAG, "System clock is before 1970; setting to 1970."); SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME); } // If the system has "persist.sys.language" and friends set, replace them with // "persist.sys.locale". Note that the default locale at this point is calculated // using the "-Duser.locale" command line flag. That flag is usually populated by // AndroidRuntime using the same set of system properties, but only the system_server // and system apps are allowed to set them. // // NOTE: Most changes made here will need an equivalent change to // core/jni/AndroidRuntime.cpp if (!SystemProperties.get("persist.sys.language").isEmpty()) { final String languageTag = Locale.getDefault().toLanguageTag(); SystemProperties.set("persist.sys.locale", languageTag); SystemProperties.set("persist.sys.language", ""); SystemProperties.set("persist.sys.country", ""); SystemProperties.set("persist.sys.localevar", ""); } // Here we go! Slog.i(TAG, "Entered the Android system server!"); EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, SystemClock.uptimeMillis()); // In case the runtime switched since last boot (such as when // the old runtime was removed in an OTA), set the system // property so that it is in sync. We can't do this in // libnativehelper's JniInvocation::Init code where we already // had to fallback to a different runtime because it is // running as root and we need to be the system user to set // the property. http://b/11463182 SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary()); // Enable the sampling profiler. if (SamplingProfilerIntegration.isEnabled()) { SamplingProfilerIntegration.start(); mProfilerSnapshotTimer = new Timer(); mProfilerSnapshotTimer.schedule(new TimerTask() { @Override public void run() { SamplingProfilerIntegration.writeSnapshot("system_server", null); } }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL); } // Mmmmmm... more memory! VMRuntime.getRuntime().clearGrowthLimit(); // The system server has to run all of the time, so it needs to be // as efficient as possible with its memory usage. VMRuntime.getRuntime().setTargetHeapUtilization(0.8f); // Some devices rely on runtime fingerprint generation, so make sure // we've defined it before booting further. Build.ensureFingerprintProperty(); // Within the system server, it is an error to access Environment paths without // explicitly specifying a user. Environment.setUserRequired(true); // Ensure binder calls into the system always run at foreground priority. BinderInternal.disableBackgroundScheduling(true); // Prepare the main looper thread (this thread). android.os.Process.setThreadPriority( android.os.Process.THREAD_PRIORITY_FOREGROUND); android.os.Process.setCanSelfBackground(false); Looper.prepareMainLooper(); // Initialize native services. System.loadLibrary("android_servers"); // Check whether we failed to shut down last time we tried. // This call may not return. performPendingShutdown(); // Initialize the system context. createSystemContext(); // Create the system service manager. mSystemServiceManager = new SystemServiceManager(mSystemContext); LocalServices.addService(SystemServiceManager.class, mSystemServiceManager); // Start services. try { startBootstrapServices(); startCoreServices(); startOtherServices(); } catch (Throwable ex) { Slog.e("System", "******************************************"); Slog.e("System", "************ Failure starting system services", ex); throw ex; } // For debug builds, log event loop stalls to dropbox for analysis. if (StrictMode.conditionallyEnableDebugLogging()) { Slog.i(TAG, "Enabled StrictMode for system server main thread."); } // Loop forever. Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } 1.1 初始化系统时间 if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) { Slog.w(TAG, "System clock is before 1970; setting to 1970."); SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME); } 1.2 设置语言，位置，国家,地区（只有系统app和系统服务可修改） if (!SystemProperties.get("persist.sys.language").isEmpty()) { final String languageTag = Locale.getDefault().toLanguageTag(); SystemProperties.set("persist.sys.locale", languageTag); SystemProperties.set("persist.sys.language", ""); SystemProperties.set("persist.sys.country", ""); SystemProperties.set("persist.sys.localevar", ""); } 1.3 接下来无关紧要，设置虚拟机运行内存，加载运行库，初始化SystemServer进程异步消息Looper Looper.prepareMainLooper(); Looper.loop(); 2 创建SystemServer系统Context private void createSystemContext() { ActivityThread activityThread = ActivityThread.systemMain(); mSystemContext = activityThread.getSystemContext(); mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar); } 3 创建SystemServiceManager，SystemServiceManager是用来初始化各种系统服务的。创建之后，并存储起来。 mSystemServiceManager = new SystemServiceManager(mSystemContext); LocalServices.addService(SystemServiceManager.class, mSystemServiceManager); 4 启动服务 startBootstrapServices 启动系统Boot级服务 startCoreServices 启动系统核心服务 startOtherServices 启动系统其他服务 // Start services. try { startBootstrapServices(); startCoreServices(); startOtherServices(); } catch (Throwable ex) { Slog.e("System", "******************************************"); Slog.e("System", "************ Failure starting system services", ex); throw ex; } 4.1 startBootstrapServices 先上源码 private void startBootstrapServices() { // 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); // Activity manager runs the show. mActivityManagerService = mSystemServiceManager.startService( ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); // Power manager needs to be started early because other services need it. // Native daemons may be watching for it to be registered so it must be ready // to handle incoming binder calls immediately (including being able to verify // the permissions for those calls). mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class); // Now that the power manager has been started, let the activity manager // initialize power management features. mActivityManagerService.initPowerManagement(); // Manages LEDs and display backlight so we need it to bring up the display. mSystemServiceManager.startService(LightsService.class); // Display manager is needed to provide display metrics before package manager // starts up. mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class); // We need the default display before we can initialize the package manager. mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY); // Only run "core" apps if we're encrypting the device. String cryptState = SystemProperties.get("vold.decrypt"); if (ENCRYPTING_STATE.equals(cryptState)) { Slog.w(TAG, "Detected encryption in progress - only parsing core apps"); mOnlyCore = true; } else if (ENCRYPTED_STATE.equals(cryptState)) { Slog.w(TAG, "Device encrypted - only parsing core apps"); mOnlyCore = true; } // Start the package manager. Slog.i(TAG, "Package Manager"); mPackageManagerService = PackageManagerService.main(mSystemContext, installer, mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore); mFirstBoot = mPackageManagerService.isFirstBoot(); mPackageManager = mSystemContext.getPackageManager(); Slog.i(TAG, "User Service"); ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance()); // Initialize attribute cache used to cache resources from packages. AttributeCache.init(mSystemContext); // Set up the Application instance for the system process and get started. mActivityManagerService.setSystemProcess(); // The sensor service needs access to package manager service, app ops // service, and permissions service, therefore we start it after them. startSensorService(); } 4.1.1 首先startService Installer installer = mSystemServiceManager.startService(Installer.class);

查看SystemServiceManager

public <T extends SystemService> T startService(Class<T> serviceClass) { final String name = serviceClass.getName(); Slog.i(TAG, "Starting " + 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); } catch (IllegalAccessException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (NoSuchMethodException ex) { throw new RuntimeException("Failed to create service " + name + ": service must have a public constructor with a Context argument", ex); } catch (InvocationTargetException ex) { throw new RuntimeException("Failed to create service " + name + ": service constructor threw an exception", 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; } 4.1.2 这里我们看到Register & Start，service是传进来的Installer类 4.1.3 Installer类是系统安装apk的服务类，需要启动Installer服务之后才可以启动其他系统服务。 所以作为第一个启动的服务。 看一下onStart() 如何调用？ @Override public void onStart() { Slog.i(TAG, "Waiting for installd to be ready."); mInstaller.waitForConnection(); } public void waitForConnection() { for (;;) { if (execute("ping") >= 0) { return; } Slog.w(TAG, "installd not ready"); SystemClock.sleep(1000); } }

4.1.4 在 waitForConnection中 创建轮询，不断通过ping命令连接 Zygote进程，因为Android中只有SystemServer和Zygote进程通过socket方式通讯，其他进程通过Binder方式通讯。 只有在 SystemServer和Zygote 成功连接后，才会启动其他的服务。

4.1.5 启动其他服务

ActivityManagerService （SystemServiceManager.startService）PowerManagerService （SystemServiceManager.startService）LightsService（SystemServiceManager.startService）DisplayManagerService（SystemServiceManager.startService）PackageManagerService（PackageManagerService.main）通过ServiceManager.addService方法启动，再通过Binder机制与JNI交互UserManagerService（ServiceManager.addService） public static PackageManagerService main(Context context, Installer installer, boolean factoryTest, boolean onlyCore) { PackageManagerService m = new PackageManagerService(context, installer, factoryTest, onlyCore); ServiceManager.addService("package", m); return m; }

4.1.6 最后 startSensorService() 完成，以上这些服务有复杂的相互依赖关系，所以放在一起进行初始化

4.2 startCoreServices() 启动无相互依赖的核心服务

BatteryServiceUsageStatsManagerInternalWebViewUpdateService private void startCoreServices() { // Tracks the battery level. Requires LightService. mSystemServiceManager.startService(BatteryService.class); // Tracks application usage stats. mSystemServiceManager.startService(UsageStatsService.class); mActivityManagerService.setUsageStatsManager( LocalServices.getService(UsageStatsManagerInternal.class)); // Update after UsageStatsService is available, needed before performBootDexOpt. mPackageManagerService.getUsageStatsIfNoPackageUsageInfo(); // Tracks whether the updatable WebView is in a ready state and watches for update installs. mSystemServiceManager.startService(WebViewUpdateService.class); }

4.3 启动其他服务 startOtherServices(),代码太长就不贴了0.0（800行）

5.梳理一下