Android系统启动-SystemServer下篇
co518248
8年前
<p>基于Android 6.0的源码剖析， 分析Android启动过程的system_server进程</p> <pre> <code class="language-java">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 </code></pre> <h3>一、启动调用栈</h3> <p>System_server启动函数调用类的栈关系：</p> <pre> <code class="language-java">SystemServer.main SystemServer.run createSystemContext ActivityThread.systemMain ActivityThread.attach LoadedApk.makeApplication ActivityThread.getSystemContext ContextImpl.createSystemContext startBootstrapServices(); startCoreServices(); startOtherServices(); Looper.loop(); </code></pre> <h3>二、 SystemServer分析</h3> <p>上一篇文章 <a href="/misc/goto?guid=4959673006685117047" rel="nofollow,noindex">Android系统启动-systemServer上篇</a> 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。</p> <p>Step 1.SystemServer.main</p> <pre> <code class="language-java">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(); } </code></pre> <p>Step 2.SystemServer.run</p> <pre> <code class="language-java">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.so SystemProperties.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() { @Override public 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0.8 VMRuntime.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sLocalServiceObjects LocalServices.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"); } </code></pre> <p>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。</p> <p>Step 3.SystemServer.createSystemContext</p> <pre> <code class="language-java">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); } </code></pre> <p>Step 3-1.ActivityThread.systemMain</p> <pre> <code class="language-java">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ActivityThread ActivityThread thread = new ActivityThread(); // 创建Application以及调用其onCreate()方法【见Step 3-1-1】 thread.attach(true); return thread; } </code></pre> <p>Step 3-1-1.ActivityThread.attach</p> <pre> <code class="language-java">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libcore DropBox.setReporter(new DropBoxReporter()); // 设置回调方法 ViewRootImpl.addConfigCallback(new ComponentCallbacks2() { @Override public void onConfigurationChanged(Configuration newConfig) { synchronized (mResourcesManager) { if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) { if (mPendingConfiguration == null || mPendingConfiguration.isOtherSeqNewer(newConfig)) { mPendingConfiguration = newConfig; sendMessage(H.CONFIGURATION_CHANGED, newConfig); } } } } @Override public void onLowMemory() { } @Override public void onTrimMemory(int level) { } }); } </code></pre> <p>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。</p> <p>Step 3-1-1-1.LoadedApk.makeApplication</p> <pre> <code class="language-java">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Application app = 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; } </code></pre> <p>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();</p> <p>Step 3-2.ActivityThread.getSystemContext</p> <pre> <code class="language-java">public ContextImpl getSystemContext() { synchronized (this) { if (mSystemContext == null) { //创建ContextImpl对象【见Step 3-2-1】 mSystemContext = ContextImpl.createSystemContext(this); } return mSystemContext; } } </code></pre> <p>Step 3-2-1.ContextImpl.createSystemContext</p> <pre> <code class="language-java">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; } </code></pre> <p>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。</p> <p>Step 4.startBootstrapServices</p> <p>[–>SystemServer.java]</p> <pre> <code class="language-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ActivityManagerService mActivityManagerService = mSystemServiceManager.startService( ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); //启动服务PowerManagerService mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class); //初始化power management mActivityManagerService.initPowerManagement(); //启动服务LightsService mSystemServiceManager.startService(LightsService.class); //启动服务DisplayManagerService mDisplayManagerService = 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PackageManagerService mPackageManagerService = 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AMS mActivityManagerService.setSystemProcess(); //启动传感器服务 startSensorService(); } </code></pre> <p>该方法所创建的服务：ActivityManagerService, PowerManagerService, LightsService, DisplayManagerService， PackageManagerService， UserManagerService， sensor服务.</p> <p>Step 5.startCoreServices</p> <pre> <code class="language-java">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WebViewUpdateService mSystemServiceManager.startService(WebViewUpdateService.class); } </code></pre> <p>启动服务BatteryService，UsageStatsService，WebViewUpdateService。</p> <p>Step 6.startOtherServices</p> <p>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。</p> <h3>三、Service启动过程</h3> <p>接下来，开始正式进入启动系统服务的过程。</p> <p>启动方式</p> <p>system_server进程中的服务启动方式有两种，</p> <ol> <li>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。</li> <li>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 <a href="/misc/goto?guid=4959673006780438290" rel="nofollow,noindex">service Manager注册服务</a> 。</li> </ol> <p>启动流程</p> <p>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：</p> <p><img src="https://simg.open-open.com/show/e2cce1603401178bbc199ffe439b27c8.jpg"></p> <p>启动流程分析：</p> <ol> <li>PHASE_WAIT_FOR_DEFAULT_DISPLAY=100 ，该阶段等待Display有默认显示;</li> <li>PHASE_LOCK_SETTINGS_READY=480 ，进入该阶段服务能获取锁屏设置的数据;</li> <li>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;</li> <li>PHASE_ACTIVITY_MANAGER_READY=550 ，进入该阶段服务能广播Intent;</li> <li>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;</li> <li>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。</li> </ol> <p>Phase 100</p> <p>创建ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService共4项服务；</p> <p>接着则进入阶段 100 ，该阶段调用DisplayManagerService的 onBootPhase() 方法。</p> <p>Phase 480&&500</p> <p>创建PackageManagerService、WindowManagerService、InputManagerService、NetworkManagerService、DropBoxManagerService/FingerprintService等服务</p> <p>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。</p> <p>Phase 550</p> <p>WindowManagerService、PowerManagerService、PackageManagerService、DisplayManagerService分别依次执行 systemReady() 方法；然后ActivityManagerService进入 systemReady() 方法;</p> <p>接着则进入阶段 550 ，实现该阶段的回调方法的服务较多。</p> <p>Phase 600</p> <p>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。</p> <p>接着则进入阶段 600 ，实现该阶段的回调方法的服务较多。</p> <p>Phase 1000</p> <p>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 。</p> <p>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。</p> <h3>四、服务分类</h3> <p>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。</p> <ol> <li>引导服务：ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService、PackageManagerService、UserManagerService、SensorService共7项服务；</li> <li>核心服务：BatteryService、UsageStatsService、WebViewUpdateService共3项服务；</li> <li>其他服务：AlarmManagerService、VibratorService等共70多项服务</li> </ol> <p>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）：</p> <ol> <li><strong>重量级服务：</strong> <strong>ActivityManagerService</strong> 、 <strong>PackageManagerService</strong> 、 <strong>WindowManagerService</strong></li> <li><strong>功耗相关：</strong> <strong>PowerManagerService</strong> 、BatteryService、BatteryStatsService、DreamManagerService</li> <li><strong>统计调度相关：</strong> <strong>DropBoxManagerService</strong> 、 <strong>SamplingProfilerService</strong> 、UsageStatsService、DiskStatsService、SchedulingPolicyService、DeviceStorageMonitorService、AlarmManagerService、DeviceIdleController、DockObserver、ThermalObserver、JobSchedulerService、AccessibilityManagerService</li> <li><strong>UI相关：</strong> DisplayManagerService、LightsService、GraphicsStatsService、StatusBarManagerService、NotificationManagerService、WallpaperManagerService、UiModeManagerService、AppWidgetService、LauncherAppsService、TextServicesManagerService、ContentService、LockSettingsService、InputManagerService、InputMethodManagerServiceMountService、FingerprintService、TvInputManagerService</li> <li><strong>网络相关：</strong> NetworkManagementService、NetworkScoreService、NetworkStatsService、NetworkPolicyManagerService、ConnectivityService、BluetoothService、WifiP2pService、WifiService、WifiScanningService、EthernetService、WebViewUpdateService</li> <li><strong>Media相关：</strong> AudioService、MediaRouterService、VoiceInteractionManagerService、MediaProjectionManagerService、MediaSessionService、</li> <li><strong>设备相关：</strong> DevicePolicyManagerService、PrintManagerService、BackupManagerService、UserManagerService、AccountManagerService、TrustManagerService、 <strong>SensorService</strong> 、LocationManagerService、VibratorService、CountryDetectorService、GestureLauncherService、PersistentDataBlockService、ClipboardService</li> <li><strong>其他：</strong> TelephonyRegistry、TelecomLoaderService、NsdService、UpdateLockService、SerialService、SearchManagerService、CommonTimeManagementService、AssetAtlasService、ConsumerIrService、MidiServiceCameraService、TwilightService、RestrictionsManagerService、MmsServiceBroker、RttService、UsbService。</li> </ol> <p>后续，会针对其中比较重要的服务进行展开详解。</p> <p>来自： <a href="/misc/goto?guid=4959673006861276674" rel="nofollow">http://gityuan.com/2016/02/20/android-system-server-2/</a></p>