Android 源码分析 SystemServer 进程

风流不在谈锋胜，袖手无言味最长。这篇文章主要讲述Android 源码分析 SystemServer 进程相关的知识，希望能为你提供帮助。
一.前言: init进程 –> Zygote进程 –> SystemServer进程 –> Launcher桌面程序 -> 我们的App应用

init进程：linux的根进程，android系统是基于linux系统的，因此可以算作是整个android操作系统的第一个进程；

Zygote进程：android系统的根进程，主要作用：可以作用Zygote进程fork出SystemServer进程和各种应用进程；

SystemService进程：主要是在这个进程中启动系统的各项服务，比如ActivityManagerService，PackageManagerService，WindowManagerService服务等等；

Launcher桌面程序:就是我们平时看到的桌面程序，它其实也是一个android应用程序，只不过这个应用程序是系统默认第一个启动的应用程序.

二. SystemService进程 ZygoteInit类的main方法调用了StartSystemService() 启动SystemService.
SystemServer进程主要的作用是启动各种系统服务，比如ActivityManagerService，PackageManagerService，WindowManagerService等服务.
【Android 源码分析 SystemServer 进程】

//ZygoteInit.java /** * Prepare the arguments and fork for the system server process. */ private static boolean startSystemServer(String abiList, String socketName, ZygoteServer zygoteServer) throws Zygote.MethodAndArgsCaller, RuntimeException { long capabilities = posixCapabilitiesAsBits( OsConstants.CAP_IPC_LOCK, OsConstants.CAP_KILL, OsConstants.CAP_NET_ADMIN, OsConstants.CAP_NET_BIND_SERVICE, OsConstants.CAP_NET_BROADCAST, OsConstants.CAP_NET_RAW, OsConstants.CAP_SYS_MODULE, OsConstants.CAP_SYS_NICE, OsConstants.CAP_SYS_PTRACE, OsConstants.CAP_SYS_TIME, OsConstants.CAP_SYS_TTY_CONFIG, OsConstants.CAP_WAKE_ALARM ); /* Containers run without this capability, so avoid setting it in that case */ if (!SystemProperties.getBoolean(PROPERTY_RUNNING_IN_CONTAINER, false)) { capabilities |= posixCapabilitiesAsBits(OsConstants.CAP_BLOCK_SUSPEND); } /* Hardcoded command line to start the system server */ String args[] = { "--setuid=1000", "--setgid=1000", "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010", "--capabilities=" + capabilities + "," + capabilities, "--nice-name=system_server", "--runtime-args", "com.android.server.SystemServer", }; ZygoteConnection.Arguments parsedArgs = null; int pid; try { parsedArgs = new ZygoteConnection.Arguments(args); ZygoteConnection.applyDebuggerSystemProperty(parsedArgs); ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs); /* Request to fork the system server process */ pid = Zygote.forkSystemServer( parsedArgs.uid, parsedArgs.gid, parsedArgs.gids, parsedArgs.debugFlags, null, parsedArgs.permittedCapabilities, parsedArgs.effectiveCapabilities); } catch (IllegalArgumentException ex) { throw new RuntimeException(ex); }/* For child process */ if (pid == 0) { if (hasSecondZygote(abiList)) { waitForSecondaryZygote(socketName); }zygoteServer.closeServerSocket(); handleSystemServerProcess(parsedArgs); }return true; }

接上篇文章继续看看SystemServer在源码中做了什么.

//SystemServer.java/** * The main entry point from zygote. */ public static void main(String[] args) { new SystemServer().run(); }private void run() { try { traceBeginAndSlog("InitBeforeStartServices"); // 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); }// // Default the timezone property to GMT if not set. // String timezoneProperty =SystemProperties.get("persist.sys.timezone"); if (timezoneProperty == null || timezoneProperty.isEmpty()) { Slog.w(TAG, "Timezone not set; setting to GMT."); SystemProperties.set("persist.sys.timezone", "GMT"); }// 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", ""); }// The system server should never make non-oneway calls Binder.setWarnOnBlocking(true); // Here we go! Slog.i(TAG, "Entered the Android system server!"); int uptimeMillis = (int) SystemClock.elapsedRealtime(); EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, uptimeMillis); if (!mRuntimeRestart) { MetricsLogger.histogram(null, "boot_system_server_init", 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 | xq oqi‘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); // Within the system server, any incoming Bundles should be defused // to avoid throwing BadParcelableException. BaseBundle.setShouldDefuse(true); // Ensure binder calls into the system always run at foreground priority. BinderInternal.disableBackgroundScheduling(true); // Increase the number of binder threads in system_server BinderInternal.setMaxThreads(sMaxBinderThreads); // 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); mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart); LocalServices.addService(SystemServiceManager.class, mSystemServiceManager); // Prepare the thread pool for init tasks that can be parallelized SystemServerInitThreadPool.get(); } finally { traceEnd(); // InitBeforeStartServices }// Start services. 启动各种需要的服务 try { traceBeginAndSlog("StartServices"); //启动系统Boot级服务 startBootstrapServices(); //启动系统核心的服务 startCoreServices(); //启动非核心的服务 startOtherServices(); SystemServerInitThreadPool.shutdown(); } catch (Throwable ex) { Slog.e("System", "******************************************"); Slog.e("System", "************ Failure starting system services", ex); throw ex; } finally { traceEnd(); }// For debug builds, log event loop stalls to dropbox for analysis. if (StrictMode.conditionallyEnableDebugLogging()) { Slog.i(TAG, "Enabled StrictMode for system server main thread."); } if (!mRuntimeRestart & & !isFirstBootOrUpgrade()) { int uptimeMillis = (int) SystemClock.elapsedRealtime(); MetricsLogger.histogram(null, "boot_system_server_ready", uptimeMillis); final int MAX_UPTIME_MILLIS = 60 * 1000; if (uptimeMillis > MAX_UPTIME_MILLIS) { Slog.wtf(SYSTEM_SERVER_TIMING_TAG, "SystemServer init took too long. uptimeMillis=" + uptimeMillis); } }// Loop forever. Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); }/** * 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() { Slog.i(TAG, "Reading configuration..."); final String TAG_SYSTEM_CONFIG = "ReadingSystemConfig"; traceBeginAndSlog(TAG_SYSTEM_CONFIG); SystemServerInitThreadPool.get().submit(SystemConfig::getInstance, TAG_SYSTEM_CONFIG); traceEnd(); // 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. traceBeginAndSlog("StartInstaller"); Installer installer = mSystemServiceManager.startService(Installer.class); traceEnd(); // In some cases after launching an app we need to access device identifiers, // therefore register the device identifier policy before the activity manager. traceBeginAndSlog("DeviceIdentifiersPolicyService"); mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class); traceEnd(); // Activity manager runs the show. traceBeginAndSlog("StartActivityManager"); mActivityManagerService = mSystemServiceManager.startService( ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); traceEnd(); // 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). traceBeginAndSlog("StartPowerManager"); mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class); traceEnd(); // Now that the power manager has been started, let the activity manager // initialize power management features. traceBeginAndSlog("InitPowerManagement"); mActivityManagerService.initPowerManagement(); traceEnd(); // Bring up recovery system in case a rescue party needs a reboot if (!SystemProperties.getBoolean("config.disable_noncore", false)) { traceBeginAndSlog("StartRecoverySystemService"); mSystemServiceManager.startService(RecoverySystemService.class); traceEnd(); }// Now that we have the bare essentials of the OS up and running, take // note that we just booted, which might send out a rescue party if // we‘re stuck in a runtime restart loop. RescueParty.noteBoot(mSystemContext); // Manages LEDs and display backlight so we need it to bring up the display. traceBeginAndSlog("StartLightsService"); mSystemServiceManager.startService(LightsService.class); traceEnd(); // Display manager is needed to provide display metrics before package manager // starts up. traceBeginAndSlog("StartDisplayManager"); mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class); traceEnd(); // We need the default display before we can initialize the package manager. traceBeginAndSlog("WaitForDisplay"); mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY); traceEnd(); // 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. if (!mRuntimeRestart) { MetricsLogger.histogram(null, "boot_package_manager_init_start", (int) SystemClock.elapsedRealtime()); } traceBeginAndSlog("StartPackageManagerService"); mPackageManagerService = PackageManagerService.main(mSystemContext, installer, mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore); mFirstBoot = mPackageManagerService.isFirstBoot(); mPackageManager = mSystemContext.getPackageManager(); traceEnd(); if (!mRuntimeRestart & & !isFirstBootOrUpgrade()) { MetricsLogger.histogram(null, "boot_package_manager_init_ready", (int) SystemClock.elapsedRealtime()); } // Manages A/B OTA dexopting. This is a bootstrap service as we need it to rename // A/B artifacts after boot, before anything else might touch/need them. // Note: this isn‘t needed during decryption (we don‘t have /data anyways). if (!mOnlyCore) { boolean disableOtaDexopt = SystemProperties.getBoolean("config.disable_otadexopt", false); if (!disableOtaDexopt) { traceBeginAndSlog("StartOtaDexOptService"); try { OtaDexoptService.main(mSystemContext, mPackageManagerService); } catch (Throwable e) { reportWtf("starting OtaDexOptService", e); } finally { traceEnd(); } } }traceBeginAndSlog("StartUserManagerService"); mSystemServiceManager.startService(UserManagerService.LifeCycle.class); traceEnd(); // Initialize attribute cache used to cache resources from packages. traceBeginAndSlog("InitAttributerCache"); AttributeCache.init(mSystemContext); traceEnd(); // Set up the Application instance for the system process and get started. traceBeginAndSlog("SetSystemProcess"); mActivityManagerService.setSystemProcess(); traceEnd(); // DisplayManagerService needs to setup android.display scheduling related policies // since setSystemProcess() would have overridden policies due to setProcessGroup mDisplayManagerService.setupSchedulerPolicies(); // Manages Overlay packages traceBeginAndSlog("StartOverlayManagerService"); mSystemServiceManager.startService(new OverlayManagerService(mSystemContext, installer)); traceEnd(); // The sensor service needs access to package manager service, app ops // service, and permissions service, therefore we start it after them. // Start sensor service in a separate thread. Completion should be checked // before using it. mSensorServiceStart = SystemServerInitThreadPool.get().submit(() -> { BootTimingsTraceLog traceLog = new BootTimingsTraceLog( SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER); traceLog.traceBegin(START_SENSOR_SERVICE); startSensorService(); traceLog.traceEnd(); }, START_SENSOR_SERVICE); }/** * Starts some essential services that are not tangled up in the bootstrap process. */ private void startCoreServices() { // Records errors and logs, for example wtf() traceBeginAndSlog("StartDropBoxManager"); mSystemServiceManager.startService(DropBoxManagerService.class); traceEnd(); traceBeginAndSlog("StartBatteryService"); // Tracks the battery level.Requires LightService. mSystemServiceManager.startService(BatteryService.class); traceEnd(); // Tracks application usage stats. traceBeginAndSlog("StartUsageService"); mSystemServiceManager.startService(UsageStatsService.class); mActivityManagerService.setUsageStatsManager( LocalServices.getService(UsageStatsManagerInternal.class)); traceEnd(); // Tracks whether the updatable WebView is in a ready state and watches for update installs. traceBeginAndSlog("StartWebViewUpdateService"); mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class); traceEnd(); }

// mSystemServiceManager是系统服务管理对象.在run()方法已经创建 mSystemServiceManager = new SystemServiceManager(mSystemContext); // 进入mSystemServiceManager.startService() 分析下. 进入具体实现的方法//SystemServiceManager.java /** * Creates and starts a system service. The class must be a subclass of * {@link com.android.server.SystemService}. * * @param serviceClass A Java class that implements the SystemService interface. * @return The service instance, never null. * @throws RuntimeException if the service fails to start. */ @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); } 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); }startService(service); return service; } finally { Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER); } }/** * Starts a service by class name. * * @return The service instance. */ @SuppressWarnings("unchecked") public SystemService startService(String className) { final Class< SystemService> serviceClass; try { serviceClass = (Class< SystemService> )Class.forName(className); } catch (ClassNotFoundException ex) { Slog.i(TAG, "Starting " + className); throw new RuntimeException("Failed to create service " + className + ": service class not found, usually indicates that the caller should " + "have called PackageManager.hasSystemFeature() to check whether the " + "feature is available on this device before trying to start the " + "services that implement it", ex); } return startService(serviceClass); }//通过反射器构造方法创建出服务类,然后返回SystemService.启动对应的服务.