Android系统启动-SystemServer下篇

转自：http://gityuan.com/2016/02/20/android-system-server-2/

基于Android 6.0的源码剖析，分析Android启动过程的system_server进程

frameworks/base/core/java/android/app/ActivityThread.java
frameworks/base/core/java/android/app/LoadedApk.java
frameworks/base/core/java/android/app/ContextImpl.java
frameworks/base/core/java/com/android/server/LocalServices.java
frameworks/base/services/java/com/android/server/SystemServer.java
frameworks/base/services/core/java/com/android/server/SystemServiceManager.java
frameworks/base/services/core/java/com/android/server/ServiceThread.java
frameworks/base/services/core/java/com/android/server/pm/Installer.java
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

一、启动调用栈

System_server启动函数调用类的栈关系：

SystemServer.mainSystemServer.runcreateSystemContextActivityThread.systemMainActivityThread.attachLoadedApk.makeApplicationActivityThread.getSystemContextContextImpl.createSystemContextstartBootstrapServices(); startCoreServices();    startOtherServices();Looper.loop();

二、 SystemServer分析

上一篇文章Android系统启动-systemServer上篇讲解了从Zygote一路启动到SystemServer的过程，本文重要是讲述system_server所承载的java framework的系统服务框架，是如何一路路启动的。

Step 1. SystemServer.main

public static void main(String[] args) {//先初始化SystemServer对象，再调用对象的run()方法， 【见Step 2】new SystemServer().run();
}

Step 2. SystemServer.run

private void run() {//当系统时间比1970年更早，就设置当前系统时间为1970年if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);}//变更虚拟机的库文件，对于Android 6.0默认采用的是libart.soSystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());//isEnabled()为true，则开启采用分析器if (SamplingProfilerIntegration.isEnabled()) {SamplingProfilerIntegration.start();mProfilerSnapshotTimer = new Timer();//system_server每隔1小时采用一次，并保存结果到system_server文件mProfilerSnapshotTimer.schedule(new TimerTask() {@Overridepublic void run() {SamplingProfilerIntegration.writeSnapshot("system_server", null);}}, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);}//清除vm内存增长上限，由于启动过程需要较多的虚拟机内存空间VMRuntime.getRuntime().clearGrowthLimit();//设置内存的可能有效使用率为0.8VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);// 针对部分设备依赖于运行时就产生指纹信息，因此需要在开机完成前已经定义Build.ensureFingerprintProperty();//访问环境变量前，需要明确地指定用户Environment.setUserRequired(true);//确保当前系统进程的binder调用，总是运行在前台优先级(foreground priority)BinderInternal.disableBackgroundScheduling(true);android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);android.os.Process.setCanSelfBackground(false);// 主线程looper就在当前线程运行Looper.prepareMainLooper();//加载android_servers.so库，该库包含的源码在frameworks/base/services/目录下System.loadLibrary("android_servers");//检测上次关机过程是否失败，该方法可能不会返回performPendingShutdown();//初始化系统上下文 【见Step 3】createSystemContext();//创建系统服务管理mSystemServiceManager = new SystemServiceManager(mSystemContext);//将mSystemServiceManager添加到本地服务的成员sLocalServiceObjectsLocalServices.addService(SystemServiceManager.class, mSystemServiceManager);//启动各种系统服务try {startBootstrapServices(); // 启动引导服务【见Step 4】startCoreServices();      // 启动核心服务【见Step 5】startOtherServices();     // 启动其他服务【见Step 6】} catch (Throwable ex) {Slog.e("System", "************ Failure starting system services", ex);throw ex;}//用于debug版本，将log事件不断循环地输出到dropbox（用于分析）if (StrictMode.conditionallyEnableDebugLogging()) {Slog.i(TAG, "Enabled StrictMode for system server main thread.");}//一直循环执行Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");
}

LocalServices通过用静态Map变量sLocalServiceObjects，来保存以服务类名为key，以具体服务对象为value的Map结构。

Step 3. SystemServer.createSystemContext

private void createSystemContext() {//创建ActivityThread对象【见Step 3-1】ActivityThread activityThread = ActivityThread.systemMain();//创建ContextImpl、LoadedApk对象【见Step 3-2】mSystemContext = activityThread.getSystemContext();//设置主题mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);
}

Step 3-1. ActivityThread.systemMain

public static ActivityThread systemMain() {//对于低内存的设备，禁用硬件加速if (!ActivityManager.isHighEndGfx()) {HardwareRenderer.disable(true);} else {HardwareRenderer.enableForegroundTrimming();}// 创建ActivityThreadActivityThread thread = new ActivityThread();// 创建Application以及调用其onCreate()方法【见Step 3-1-1】thread.attach(true);return thread;
}

Step 3-1-1. ActivityThread.attach

private void attach(boolean system) {sCurrentActivityThread = this;mSystemThread = system;if (!system) {...} else {//system=true,进入此分支android.ddm.DdmHandleAppName.setAppName("system_process",UserHandle.myUserId());try {mInstrumentation = new Instrumentation();// 创建应用上下文ContextImpl context = ContextImpl.createAppContext(this, getSystemContext().mPackageInfo);//创建Application 【见Step 3-1-1-1】mInitialApplication = context.mPackageInfo.makeApplication(true, null);//调用Application.onCreate()方法mInitialApplication.onCreate();} catch (Exception e) {throw new RuntimeException("Unable to instantiate Application():" + e.toString(), e);}}//添加dropbox log信息到libcoreDropBox.setReporter(new DropBoxReporter());// 设置回调方法ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {@Overridepublic void onConfigurationChanged(Configuration newConfig) {synchronized (mResourcesManager) {if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) {if (mPendingConfiguration == null ||mPendingConfiguration.isOtherSeqNewer(newConfig)) {mPendingConfiguration = newConfig;sendMessage(H.CONFIGURATION_CHANGED, newConfig);}}}}@Overridepublic void onLowMemory() {}@Overridepublic void onTrimMemory(int level) {}});
}

主要工作是创建应用上下文ContextImpl，创建Application以及调用其onCreate()方法，设置DropBox以及ComponentCallbacks2回调方法。

Step 3-1-1-1. LoadedApk.makeApplication

public Application makeApplication(boolean forceDefaultAppClass,Instrumentation instrumentation) {if (mApplication != null) {return mApplication;}Application app = null;String appClass = mApplicationInfo.className;if (forceDefaultAppClass || (appClass == null)) {appClass = "android.app.Application"; //设置class名}try {java.lang.ClassLoader cl = getClassLoader();if (!mPackageName.equals("android")) {initializeJavaContextClassLoader(); //不进入该分支}ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);// 创建Applicationapp = mActivityThread.mInstrumentation.newApplication(cl, appClass, appContext);appContext.setOuterContext(app);} catch (Exception e) {...}// 将前面创建的app添加到应用列表。mActivityThread.mAllApplications.add(app);mApplication = app;...return app;
}

在该方法调用之前，已经创建了LoadedApk对象，该对象的成员变量mPackageName=”android”; mClassLoader = ClassLoader.getSystemClassLoader();

Step 3-2. ActivityThread.getSystemContext

public ContextImpl getSystemContext() {synchronized (this) {if (mSystemContext == null) {//创建ContextImpl对象【见Step 3-2-1】mSystemContext = ContextImpl.createSystemContext(this);}return mSystemContext;}
}

Step 3-2-1. ContextImpl.createSystemContext

static ContextImpl createSystemContext(ActivityThread mainThread) {//创建LoadedApk对象LoadedApk packageInfo = new LoadedApk(mainThread);//创建ContextImpl对象ContextImpl context = new ContextImpl(null, mainThread,packageInfo, null, null, false, null, null, Display.INVALID_DISPLAY);context.mResources.updateConfiguration(context.mResourcesManager.getConfiguration(), context.mResourcesManager.getDisplayMetricsLocked());return context;
}

运行到这里，system_server的准备环境基本完成，接下来开始system_server中最为核心的过程，启动系统服务。通过startBootstrapServices(), startCoreServices(), startOtherServices()3个方法。

Step 4. startBootstrapServices

[–>SystemServer.java]

private void startBootstrapServices() {//阻塞等待与installd建立socket通道Installer installer = mSystemServiceManager.startService(Installer.class);//启动服务ActivityManagerServicemActivityManagerService = mSystemServiceManager.startService(ActivityManagerService.Lifecycle.class).getService();mActivityManagerService.setSystemServiceManager(mSystemServiceManager);mActivityManagerService.setInstaller(installer);//启动服务PowerManagerServicemPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);//初始化power managementmActivityManagerService.initPowerManagement();//启动服务LightsService mSystemServiceManager.startService(LightsService.class);//启动服务DisplayManagerServicemDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);//在初始化package manager之前，需要默认的显示mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);//当设备正在加密时，仅运行核心String cryptState = SystemProperties.get("vold.decrypt");if (ENCRYPTING_STATE.equals(cryptState)) {mOnlyCore = true;} else if (ENCRYPTED_STATE.equals(cryptState)) {mOnlyCore = true;}//启动服务PackageManagerServicemPackageManagerService = PackageManagerService.main(mSystemContext, installer,mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);mFirstBoot = mPackageManagerService.isFirstBoot();mPackageManager = mSystemContext.getPackageManager();//启动服务UserManagerService，新建目录/data/user/ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance());AttributeCache.init(mSystemContext);//设置AMSmActivityManagerService.setSystemProcess();//启动传感器服务startSensorService();
}

该方法所创建的服务：ActivityManagerService, PowerManagerService, LightsService, DisplayManagerService， PackageManagerService， UserManagerService， sensor服务.

Step 5. startCoreServices

private void startCoreServices() {//启动服务BatteryService，用于统计电池电量，需要LightService.mSystemServiceManager.startService(BatteryService.class);//启动服务UsageStatsService，用于统计应用使用情况mSystemServiceManager.startService(UsageStatsService.class);mActivityManagerService.setUsageStatsManager(LocalServices.getService(UsageStatsManagerInternal.class));mPackageManagerService.getUsageStatsIfNoPackageUsageInfo();//启动服务WebViewUpdateServicemSystemServiceManager.startService(WebViewUpdateService.class);
}

启动服务BatteryService，UsageStatsService，WebViewUpdateService。

Step 6. startOtherServices

该方法比较长，有近千行代码，逻辑很简单，主要是启动一系列的服务，这里就不列举源码了，在第四节直接对其中的服务进行一个简单分类。

三、Service启动过程

接下来，开始正式进入启动系统服务的过程。

启动方式

system_server进程中的服务启动方式有两种，

一种是通过SystemServiceManager的startService()，该方法用于启动继承于SystemService的服务。主要功能：创建serviceClass类的对象，将刚创建对象添加到SystemServiceManager的成员变量mServices，再调用刚创建对象的onStart()方法。对于服务启动到一定阶段，进入相应的Phase时，会调用SystemServiceManager的startBootPhase()回调方法，该方法会循环遍历所有向SystemServiceManager注册过的service的onBootPhase()方法。
另一种是通过ServiceManager的addService(String name, IBinder service)，该方法用于初始化继承于IBinder的服务。主要功能将该服务向Native层的service Manager注册服务。

启动流程

SystemServiceManager的startBootPhase(）方法贯穿整个阶段，启动阶段从PHASE_WAIT_FOR_DEFAULT_DISPLAY到PHASE_BOOT_COMPLETED，如下图：

启动流程分析：

PHASE_WAIT_FOR_DEFAULT_DISPLAY=100，该阶段等待Display有默认显示;
PHASE_LOCK_SETTINGS_READY=480，进入该阶段服务能获取锁屏设置的数据;
PHASE_SYSTEM_SERVICES_READY=500，进入该阶段服务能安全地调用核心系统服务，如PMS;
PHASE_ACTIVITY_MANAGER_READY=550，进入该阶段服务能广播Intent;
PHASE_THIRD_PARTY_APPS_CAN_START=600，进入该阶段服务能start/bind第三方apps，app能通过BInder调用service;
PHASE_BOOT_COMPLETED=1000，该阶段是发生在Boot完成和home应用启动完毕。系统服务更倾向于监听该阶段，而不是注册广播ACTION_BOOT_COMPLETED，从而降低系统延迟。

Phase 100

创建ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService共4项服务；

接着则进入阶段100，该阶段调用DisplayManagerService的onBootPhase()方法。

Phase 480&&500

创建PackageManagerService、WindowManagerService、InputManagerService、NetworkManagerService、DropBoxManagerService/FingerprintService等服务

接着则进入阶段480，该阶段调用DevicePolicyManagerService的onBootPhase()方法；紧接着进入阶段500，实现该阶段的回调方法的服务较多。

Phase 550

WindowManagerService、PowerManagerService、PackageManagerService、DisplayManagerService分别依次执行systemReady()方法；然后ActivityManagerService进入systemReady()方法;

接着则进入阶段550，实现该阶段的回调方法的服务较多。

Phase 600

AMS启动native crash监控,，加载WebView，启动SystemUi；然后是NetworkScoreService、NetworkManagementService、NetworkStatsService、NetworkPolicyManagerService、ConnectivityService、AudioService分别依次执行systemReady()方法，然后是启动Watchdog。

接着则进入阶段600，实现该阶段的回调方法的服务较多。

Phase 1000

WallpaperManagerService、InputMethodManagerService、LocationManagerService、CountryDetectorService、NetworkTimeUpdateService、CommonTimeManagementService、TextServicesManagerService、AssetAtlasService、InputManagerService、TelephonyRegistry、MediaRouterService、MmsServiceBroker这些服务依次执行其systemRunning()方法。经过一定流程，当ActivityManagerServer进入finishBooting()时，则启动流程进入阶段PHASE_BOOT_COMPLETED=1000。

到此所有服务启动完成，system_server进程启动完成，则进入Looper.loop()状态，随时待命，等待MessageQueue中的消息到来，则马上进入执行状态。

四、服务分类

system_server进程，从源码角度划分为引导服务、核心服务、其他服务3类。

引导服务：ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService、PackageManagerService、UserManagerService、SensorService共7项服务；
核心服务：BatteryService、UsageStatsService、WebViewUpdateService共3项服务；
其他服务：AlarmManagerService、VibratorService等共70多项服务

合计总大约80多个服务，下面只是简单地对所有服务分类（个人划分，便于后期分析）：

重量级服务：ActivityManagerService、PackageManagerService、WindowManagerService
功耗相关：PowerManagerService、BatteryService、BatteryStatsService、DreamManagerService
统计调度相关：DropBoxManagerService、SamplingProfilerService、UsageStatsService、DiskStatsService、SchedulingPolicyService、DeviceStorageMonitorService、AlarmManagerService、DeviceIdleController、DockObserver、ThermalObserver、JobSchedulerService、AccessibilityManagerService
UI相关：DisplayManagerService、LightsService、GraphicsStatsService、StatusBarManagerService、NotificationManagerService、WallpaperManagerService、UiModeManagerService、AppWidgetService、LauncherAppsService、TextServicesManagerService、ContentService、LockSettingsService、InputManagerService、InputMethodManagerServiceMountService、FingerprintService、TvInputManagerService
网络相关：NetworkManagementService、NetworkScoreService、NetworkStatsService、NetworkPolicyManagerService、ConnectivityService、BluetoothService、WifiP2pService、WifiService、WifiScanningService、EthernetService、WebViewUpdateService
Media相关：AudioService、MediaRouterService、VoiceInteractionManagerService、MediaProjectionManagerService、MediaSessionService、
设备相关：DevicePolicyManagerService、PrintManagerService、BackupManagerService、UserManagerService、AccountManagerService、TrustManagerService、SensorService、LocationManagerService、VibratorService、CountryDetectorService、GestureLauncherService、PersistentDataBlockService、ClipboardService
其他：TelephonyRegistry、TelecomLoaderService、NsdService、UpdateLockService、SerialService、SearchManagerService、CommonTimeManagementService、AssetAtlasService、ConsumerIrService、MidiServiceCameraService、TwilightService、RestrictionsManagerService、MmsServiceBroker、RttService、UsbService。

后续，会针对其中比较重要的服务进行展开详解。