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转：Android系统之System Server大纲

转：Android系统之System Server大纲

作者: Kevin_Gao | 来源:发表于2018-07-17 19:18 被阅读0次

Android系统之System Server大纲

System Server content

前言

System Server是android 基本服务的提供者，是android系统运行的最基本需求，所有server运行在一个叫system_process的进程中，system_process进程是android java虚拟机跑的第一个进程，从Zygote 创建而来，是andorid系统最重要的java虚拟机。可以说，整个android系统的业务都是围绕system server而展开，所以，当system_process死掉了，手机必须重启。

System server概要

System server主要包含以下服务：

  • 1、 EntropyService， 熵服务，用于产生随机数；
  • 2、 PowerManagerService， 电源管理服务；
  • 3、 ActivityMangerService Activity，管理服务；
  • 4、 TelephonyRegistry， 电话服务，电话底层通知服务；
  • 5、 PackageManagerService， 程序包管理服务；
  • 6、 AccountManagerService， 联系人账户管理服务；
  • 7、 ContentService， 内容提供器服务，提供跨进程数据交换；
  • 8、 LightService， 光感应传感器服务；
  • 9、 BatteryService，电池服务；
  • 10、 VibrateService，震动器服务；
  • 11、 AlarmManagerService，闹钟服务；
  • 12、 WindowManagerService，窗口管理服务；
  • 13、 BluetoothService，蓝牙服务；
  • 14、 InputMethodManagerService，输入法服务；
  • 15、 AccessibilityManagerService， 辅助器管理程序服务；
  • 16、 DevicePolicyManagerService，提供系统级别的设置及属性；
  • 17、 StatusBarManagerService，状态栏管理服务；
  • 18、 ClipboardService，粘贴板服务；
  • 19、 NetworkManagerService，网络管理服务；
  • 20、 TextServicesManagerService，用户管理服务；
  • 21、 NetworkStatsService，手机网络状态服务；
  • 22、 NetworkPolicyManagerService，low-level网络策略服务；
  • 23、 WifiP2pService，Wifi点对点服务；
  • 24、 WifiService，Wifi服务；
  • 25、 ConnectivityService，网络连接状态服务；
  • 26、 MountService，磁盘加载服务；
  • 27、 NotificationManagerService，通知管理服务；
  • 28、 DeviceStorageMonitorService，存储设备容量监听服务；
  • 29、 LocationManagerService，位置管理服务；
  • 30、 CountryDetectorService，检查用户当前所在国家服务；
  • 31、 SearchManagerService，搜索管理服务；
  • 32、 DropBoxManagerService，系统日志文件管理服务；
  • 33、 WallpaperManagerService，壁纸管理服务；
  • 34、 AudioService，AudioFlinger上层封装音频管理服务；
  • 35、 UsbService，USB Host 和 device管理服务；
  • 36、 UiModeManagerService，UI模式管理服务；
  • 37、 BackupManagerService，备份服务；
  • 38、 AppWidgetService，应用桌面部件服务；
  • 39、 RecognitionManagerService，身份识别服务；
  • 40、 DiskStatsService，磁盘统计服务；
  • 41、 SamplingProfilerService，性能统计服务；
  • 42、 NetworkTimeUpdateService，网络时间更新服务；
  • 43、 InputManagerService，输入管理服务；
  • 44、 FingerprintService，指纹服务；
  • 45、 DreamManagerService， dreams服务；
  • 46、 HdmiControlService， HDMI控制服务；
  • 47、 SsvService，SIM卡状态和转换服务；

以上所列系统服务不代表最新Android系统的所有系统服务。

System server启动的入口

这些服务那么重要，它们什么时候启动？都做了些什么事情？等等这些问题是本文以及大纲下面的文章将会一一道来。

了解这些系统服务之前，先来了解一个重量级的超级类SystemServer.java， 这个类在AOSP中的路径是：frameworks/base/services/java/com/android/server/SystemServer.java，在上文中提到，从Zygote创建system_process进程时，便实例化了该类。熟悉java的开发者都知道，启动某个java程序时，最先调用的就是声明了main()方法的类。所以SystemServer.java被实例化后，便调用了main()方法。首先看看SystemServer.java的构造方法：

public SystemServer() {
    // Check for factory test mode.
    mFactoryTestMode = FactoryTest.getMode();
}

构造方法里面只做了从属性系统中读取了工厂测试模式，这个不在本文以及本大纲的文章中赘述的内容，这里就不在叙述了。

下面直接进入main()方法：

public static void main(String[] args) {
    new SystemServer().run();
}

直接调用了类内的run()方法，继续跟踪：

private void run() {
    try {
        // AndroidRuntime using the same set of system properties, but only the system_server
        // Initialize the system context.
        createSystemContext();

        // Create the system service manager.
        mSystemServiceManager = new SystemServiceManager(mSystemContext);
        LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
    }

    // Start services.
    try {
        Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartServices");
        startBootstrapServices();
        startCoreServices();
        startOtherServices();
    } catch (Throwable ex) {
        Slog.e("System", "******************************************");
        Slog.e("System", "************ Failure starting system services", ex);
        throw ex;
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
    }
    .....
}

上述代码中，首先创建一个system context，这个对象在整个system server中使用非常频繁。接着创建一个SystemServiceManager.java的实例，顾名思义就是SystemService的管理者，管理所有的SystemService。代码中把接着创建一个SystemServiceManager的实例通过LocalServices.addService(SystemServiceManager.class, mSystemServiceManager)语句设置到LocalService中，LocalServices的功能类似SystemServiceManager，不同点在于LocalServices专门用来管理system_process进程中的SystemService，也就没有真正的跨进程通信，也就没有Binder对象。

System server启动的过程

接着就是启动各种系统服务，在这里分三种类型的SystemService，依次启动，分别对应三个方法：

        startBootstrapServices();
        startCoreServices();
        startOtherServices();

这三个方法的顺序不能混乱，一定要按照上述顺序依次执行，先看startBootstrapServices()中启动了那些系统服务

private void startBootstrapServices() {
    Installer installer = mSystemServiceManager.startService(Installer.class);

    // Activity manager runs the show.
    mActivityManagerService = mSystemServiceManager.startService(
            ActivityManagerService.Lifecycle.class).getService();
    mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
    mActivityManagerService.setInstaller(installer);

    mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);

    Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "InitPowerManagement");
    mActivityManagerService.initPowerManagement();
    Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

    // 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);

    ......

    // Start the package manager.
    .....

    traceBeginAndSlog("StartUserManagerService");
    mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
    ......
}

上述代码可以看到，这里启动了

  • Installer
  • ActivityManagerService.Lifecycle
  • PowerManagerService
  • LightsService
  • DisplayManagerService
  • UserManagerService

启动这些SystemService都是通过SystemServiceManager的startService()的方式启动，启动完成后会回调SystemService的onStart()方法。
继续看第二个方法startCoreServices()启动了那些系统服务

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));

    // Tracks whether the updatable WebView is in a ready state and watches for update installs.
    mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
}

startCoreServices()中启动了

  • BatteryService
  • UsageStatsService
  • WebViewUpdateService

上文中提到，startBootstrapServices()必须在startCoreServices()前面执行，这里就能找到一个原因，startCoreServices()中用到mActivityManagerService对象，而该对象在startBootstrapServices()中被实例化，如果先调用startCoreServices()，mActivityManagerService对象便会发生NullPointerException的RuntimeException异常。

接着就是startOtherServices()中启动的service了，先看代码

private void startOtherServices() {
    try {
        ServiceManager.addService("scheduling_policy", new SchedulingPolicyService());

        mSystemServiceManager.startService(TelecomLoaderService.class);

        traceBeginAndSlog("StartTelephonyRegistry");
        telephonyRegistry = new TelephonyRegistry(context);
        ServiceManager.addService("telephony.registry", telephonyRegistry);
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

        mEntropyMixer = new EntropyMixer(context);

        mContentResolver = context.getContentResolver();

        mSystemServiceManager.startService(CameraService.class);

        mSystemServiceManager.startService(ACCOUNT_SERVICE_CLASS);

        mSystemServiceManager.startService(CONTENT_SERVICE_CLASS);

        mActivityManagerService.installSystemProviders();

        vibrator = new VibratorService(context);
        ServiceManager.addService("vibrator", vibrator);

        consumerIr = new ConsumerIrService(context);
        ServiceManager.addService(Context.CONSUMER_IR_SERVICE, consumerIr);

        mSystemServiceManager.startService(AlarmManagerService.class);

        final Watchdog watchdog = Watchdog.getInstance();
        watchdog.init(context, mActivityManagerService);

        traceBeginAndSlog("StartInputManagerService");
        inputManager = new InputManagerService(context);
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

        wm = WindowManagerService.main(context, inputManager,
                mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
                !mFirstBoot, mOnlyCore);
        ServiceManager.addService(Context.WINDOW_SERVICE, wm);
        ServiceManager.addService(Context.INPUT_SERVICE, inputManager);

        mSystemServiceManager.startService(VrManagerService.class);

        mActivityManagerService.setWindowManager(wm);

        inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
        inputManager.start();

        // TODO: Use service dependencies instead.
        mDisplayManagerService.windowManagerAndInputReady();

        .....
            mSystemServiceManager.startService(BluetoothService.class);
        .....

        mSystemServiceManager.startService(MetricsLoggerService.class);

        mSystemServiceManager.startService(PinnerService.class);
    } catch (RuntimeException e) {
    }
    // Bring up services needed for UI.
    if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
        mSystemServiceManager.startService(InputMethodManagerService.Lifecycle.class);

        traceBeginAndSlog("StartAccessibilityManagerService");
        try {
            ServiceManager.addService(Context.ACCESSIBILITY_SERVICE,
                    new AccessibilityManagerService(context));
        } catch (Throwable e) {
        }
    }
    if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
        if (!disableStorage &&
            !"0".equals(SystemProperties.get("system_init.startmountservice"))) {
            try {
                mSystemServiceManager.startService(MOUNT_SERVICE_CLASS);
                mountService = IMountService.Stub.asInterface(
                        ServiceManager.getService("mount"));
            } catch (Throwable e) {
                reportWtf("starting Mount Service", e);
            }
        }
    }
    mSystemServiceManager.startService(UiModeManagerService.class);
    .....

    if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
        if (!disableNonCoreServices) {
            try {
                mSystemServiceManager.startService(LOCK_SETTINGS_SERVICE_CLASS);
                lockSettings = ILockSettings.Stub.asInterface(
                        ServiceManager.getService("lock_settings"));
            } catch (Throwable e) {
            }

            if (!SystemProperties.get(PERSISTENT_DATA_BLOCK_PROP).equals("")) {
                mSystemServiceManager.startService(PersistentDataBlockService.class);
            }

            mSystemServiceManager.startService(DeviceIdleController.class);
            mSystemServiceManager.startService(DevicePolicyManagerService.Lifecycle.class);
        }

        if (!disableSystemUI) {
            try {
                statusBar = new StatusBarManagerService(context, wm);
                ServiceManager.addService(Context.STATUS_BAR_SERVICE, statusBar);
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices) {
            try {
                ServiceManager.addService(Context.CLIPBOARD_SERVICE,
                        new ClipboardService(context));
            } catch (Throwable e) {
            }
        }

        if (!disableNetwork) {
            try {
                networkManagement = NetworkManagementService.create(context);
                ServiceManager.addService(Context.NETWORKMANAGEMENT_SERVICE, networkManagement);
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices && !disableTextServices) {
            mSystemServiceManager.startService(TextServicesManagerService.Lifecycle.class);
        }

        if (!disableNetwork) {
            traceBeginAndSlog("StartNetworkScoreService");
            try {
                networkScore = new NetworkScoreService(context);
                ServiceManager.addService(Context.NETWORK_SCORE_SERVICE, networkScore);
            } catch (Throwable e) {
            }
            try {
                networkStats = NetworkStatsService.create(context, networkManagement);
                ServiceManager.addService(Context.NETWORK_STATS_SERVICE, networkStats);
            } catch (Throwable e) {
            }

            try {
                networkPolicy = new NetworkPolicyManagerService(
                        context, mActivityManagerService,
                        (IPowerManager)ServiceManager.getService(Context.POWER_SERVICE),
                        networkStats, networkManagement);
                ServiceManager.addService(Context.NETWORK_POLICY_SERVICE, networkPolicy);
            } catch (Throwable e) {
            }

            if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI_NAN)) {
                mSystemServiceManager.startService(WIFI_NAN_SERVICE_CLASS);
            } else {
                Slog.i(TAG, "No Wi-Fi NAN Service (NAN support Not Present)");
            }
            mSystemServiceManager.startService(WIFI_P2P_SERVICE_CLASS);
            mSystemServiceManager.startService(WIFI_SERVICE_CLASS);
            mSystemServiceManager.startService(
                        "com.android.server.wifi.scanner.WifiScanningService");

            if (!disableRtt) {
                mSystemServiceManager.startService("com.android.server.wifi.RttService");
            }

            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_ETHERNET) ||
                mPackageManager.hasSystemFeature(PackageManager.FEATURE_USB_HOST)) {
                mSystemServiceManager.startService(ETHERNET_SERVICE_CLASS);
            }

            traceBeginAndSlog("StartConnectivityService");
            try {
                connectivity = new ConnectivityService(
                        context, networkManagement, networkStats, networkPolicy);
                ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);
                networkStats.bindConnectivityManager(connectivity);
                networkPolicy.bindConnectivityManager(connectivity);
            } catch (Throwable e) {
            }

            try {
                serviceDiscovery = NsdService.create(context);
                ServiceManager.addService(
                        Context.NSD_SERVICE, serviceDiscovery);
            } catch (Throwable e) {
                reportWtf("starting Service Discovery Service", e);
        }

        if (!disableNonCoreServices) {
            try {
                ServiceManager.addService(Context.UPDATE_LOCK_SERVICE,
                        new UpdateLockService(context));
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices) {
            mSystemServiceManager.startService(RecoverySystemService.class);
        }
        ......

        mSystemServiceManager.startService(NotificationManagerService.class);
        notification = INotificationManager.Stub.asInterface(
                ServiceManager.getService(Context.NOTIFICATION_SERVICE));
        networkPolicy.bindNotificationManager(notification);

        mSystemServiceManager.startService(DeviceStorageMonitorService.class);

        if (!disableLocation) {
            try {
                location = new LocationManagerService(context);
                ServiceManager.addService(Context.LOCATION_SERVICE, location);
            } catch (Throwable e) {
            }
            try {
                countryDetector = new CountryDetectorService(context);
                ServiceManager.addService(Context.COUNTRY_DETECTOR, countryDetector);
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices && !disableSearchManager) {
            traceBeginAndSlog("StartSearchManagerService");
            try {
                mSystemServiceManager.startService(SEARCH_MANAGER_SERVICE_CLASS);
            } catch (Throwable e) {
            }
        }

        mSystemServiceManager.startService(DropBoxManagerService.class);

        if (!disableNonCoreServices && context.getResources().getBoolean(
                    R.bool.config_enableWallpaperService)) {
            mSystemServiceManager.startService(WALLPAPER_SERVICE_CLASS);
        }

        mSystemServiceManager.startService(AudioService.Lifecycle.class);

        if (!disableNonCoreServices) {
            mSystemServiceManager.startService(DockObserver.class);

            if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_WATCH)) {
                mSystemServiceManager.startService(THERMAL_OBSERVER_CLASS);
            }
        }
        try {
            // Listen for wired headset changes
            inputManager.setWiredAccessoryCallbacks(
                    new WiredAccessoryManager(context, inputManager));
        } catch (Throwable e) {
        }

        if (!disableNonCoreServices) {
            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_MIDI)) {
                // Start MIDI Manager service
                mSystemServiceManager.startService(MIDI_SERVICE_CLASS);
            }

            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_USB_HOST)
                    || mPackageManager.hasSystemFeature(
                            PackageManager.FEATURE_USB_ACCESSORY)) {
                mSystemServiceManager.startService(USB_SERVICE_CLASS);
            }

            if (!disableSerial) {
                try {
                    // Serial port support
                    serial = new SerialService(context);
                    ServiceManager.addService(Context.SERIAL_SERVICE, serial);
                } catch (Throwable e) {
                }
            }

                    "StartHardwarePropertiesManagerService");
            try {
                hardwarePropertiesService = new HardwarePropertiesManagerService(context);
                ServiceManager.addService(Context.HARDWARE_PROPERTIES_SERVICE,
                        hardwarePropertiesService);
            } catch (Throwable e) {
                Slog.e(TAG, "Failure starting HardwarePropertiesManagerService", e);
            }
        }

        mSystemServiceManager.startService(TwilightService.class);

        mSystemServiceManager.startService(JobSchedulerService.class);

        mSystemServiceManager.startService(SoundTriggerService.class);

        if (!disableNonCoreServices) {
            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_BACKUP)) {
                mSystemServiceManager.startService(BACKUP_MANAGER_SERVICE_CLASS);
            }

            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_APP_WIDGETS)
                || context.getResources().getBoolean(R.bool.config_enableAppWidgetService)) {
                mSystemServiceManager.startService(APPWIDGET_SERVICE_CLASS);
            }

            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_VOICE_RECOGNIZERS)) {
                mSystemServiceManager.startService(VOICE_RECOGNITION_MANAGER_SERVICE_CLASS);
            }

            if (GestureLauncherService.isGestureLauncherEnabled(context.getResources())) {
                Slog.i(TAG, "Gesture Launcher Service");
                mSystemServiceManager.startService(GestureLauncherService.class);
            }
            mSystemServiceManager.startService(SensorNotificationService.class);
            mSystemServiceManager.startService(ContextHubSystemService.class);
        }

        try {
            ServiceManager.addService("diskstats", new DiskStatsService(context));
        } catch (Throwable e) {
        }

        if (!disableSamplingProfiler) {
            traceBeginAndSlog("StartSamplingProfilerService");
            try {
                ServiceManager.addService("samplingprofiler",
                            new SamplingProfilerService(context));
            } catch (Throwable e) {
            }
        }

        if (!disableNetwork && !disableNetworkTime) {
            traceBeginAndSlog("StartNetworkTimeUpdateService");
            try {
                networkTimeUpdater = new NetworkTimeUpdateService(context);
                ServiceManager.addService("network_time_update_service", networkTimeUpdater);
            } catch (Throwable e) {
            }
        }

        traceBeginAndSlog("StartCommonTimeManagementService");
        try {
            commonTimeMgmtService = new CommonTimeManagementService(context);
            ServiceManager.addService("commontime_management", commonTimeMgmtService);
        } catch (Throwable e) {
        }
        Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

        if (!disableNetwork) {
            try {
                CertBlacklister blacklister = new CertBlacklister(context);
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices) {
            mSystemServiceManager.startService(DreamManagerService.class);
        }

        if (!disableNonCoreServices && ZygoteInit.PRELOAD_RESOURCES) {
            traceBeginAndSlog("StartAssetAtlasService");
            try {
                atlas = new AssetAtlasService(context);
                ServiceManager.addService(AssetAtlasService.ASSET_ATLAS_SERVICE, atlas);
            } catch (Throwable e) {
            }
        }

        if (!disableNonCoreServices) {
            ServiceManager.addService(GraphicsStatsService.GRAPHICS_STATS_SERVICE,
                    new GraphicsStatsService(context));
        }

        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_PRINTING)) {
            mSystemServiceManager.startService(PRINT_MANAGER_SERVICE_CLASS);
        }

        mSystemServiceManager.startService(RestrictionsManagerService.class);

        mSystemServiceManager.startService(MediaSessionService.class);

        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_HDMI_CEC)) {
            mSystemServiceManager.startService(HdmiControlService.class);
        }

        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_LIVE_TV)) {
            mSystemServiceManager.startService(TvInputManagerService.class);
        }

        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_PICTURE_IN_PICTURE)) {
            mSystemServiceManager.startService(MediaResourceMonitorService.class);
        }

        if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_LEANBACK)) {
            mSystemServiceManager.startService(TvRemoteService.class);
        }

        if (!disableNonCoreServices) {
            traceBeginAndSlog("StartMediaRouterService");
            try {
                mediaRouter = new MediaRouterService(context);
                ServiceManager.addService(Context.MEDIA_ROUTER_SERVICE, mediaRouter);
            } catch (Throwable e) {
            }

            if (!disableTrustManager) {
                mSystemServiceManager.startService(TrustManagerService.class);
            }

            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) {
                mSystemServiceManager.startService(FingerprintService.class);
            }
        }
        // LauncherAppsService uses ShortcutService.
        mSystemServiceManager.startService(ShortcutService.Lifecycle.class);

        mSystemServiceManager.startService(LauncherAppsService.class);
    }

    if (!disableNonCoreServices && !disableMediaProjection) {
        mSystemServiceManager.startService(MediaProjectionManagerService.class);
    }

    if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_WATCH)) {
        mSystemServiceManager.startService(WEAR_BLUETOOTH_SERVICE_CLASS);
    }
    mmsService = mSystemServiceManager.startService(MmsServiceBroker.class);

    // It is now time to start up the app processes...

    try {
        vibrator.systemReady();
    } catch (Throwable e) {
    }

    if (lockSettings != null) {
        try {
            lockSettings.systemReady();
        } catch (Throwable e) {
        }
    }

    // Needed by DevicePolicyManager for initialization
    mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);

    mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);

    Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeWindowManagerServiceReady");
    try {
        wm.systemReady();
    } catch (Throwable e) {
    }
    try {
        // TODO: use boot phase
        mPowerManagerService.systemReady(mActivityManagerService.getAppOpsService());
    } catch (Throwable e) {
    }

    try {
        mPackageManagerService.systemReady();
    } catch (Throwable e) {
    }

    try {
        // TODO: use boot phase and communicate these flags some other way
        mDisplayManagerService.systemReady(safeMode, mOnlyCore);
    } catch (Throwable e) {
    }
    mActivityManagerService.systemReady(new Runnable() {
        @Override
        public void run() {
            try {
                startSystemUi(context);
            } catch (Throwable e) {
            }
            "MakeNetworkManagementServiceReady");
            try {
                if (networkManagementF != null) networkManagementF.systemReady();
            } catch (Throwable e) {
                reportWtf("making Network Managment Service ready", e);
            }
            "MakeNetworkStatsServiceReady");
            try {
                if (networkStatsF != null) networkStatsF.systemReady();
            } catch (Throwable e) {
            }
            try {
                if (networkPolicyF != null) networkPolicyF.systemReady();
            } catch (Throwable e) {
                reportWtf("making Network Policy Service ready", e);
            }
            "MakeConnectivityServiceReady");
            try {
                if (connectivityF != null) connectivityF.systemReady();
            } catch (Throwable e) {
            }
            Watchdog.getInstance().start();

            try {
                if (locationF != null) locationF.systemRunning();
            } catch (Throwable e) {
            }
            try {
                if (countryDetectorF != null) countryDetectorF.systemRunning();
            } catch (Throwable e) {
            }
            try {
                if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemRunning();
            } catch (Throwable e) {
            }
            try {
                if (commonTimeMgmtServiceF != null) {
                    commonTimeMgmtServiceF.systemRunning();
                }
            } catch (Throwable e) {
            }
            try {
                if (atlasF != null) atlasF.systemRunning();
            } catch (Throwable e) {
            }
            try {
                // TODO(BT) Pass parameter to input manager
                if (inputManagerF != null) inputManagerF.systemRunning();
            } catch (Throwable e) {
            }
            try {
                if (telephonyRegistryF != null) telephonyRegistryF.systemRunning();
            } catch (Throwable e) {
                reportWtf("Notifying TelephonyRegistry running", e);
            }
            try {
                if (mediaRouterF != null) mediaRouterF.systemRunning();
            } catch (Throwable e) {
            }

            try {
                if (mmsServiceF != null) mmsServiceF.systemRunning();
            } catch (Throwable e) {
            }

            try {
                if (networkScoreF != null) networkScoreF.systemRunning();
            } catch (Throwable e) {
            }
        }
    });
}

这个方法中启动的service非常多，代码量非常巨大，所以可见，这个方法对于Android系统而言，不言也可知其重要性。由于代码量巨大，将startOtherServices()分成三部分解说：

1.startOtherServices()中启动了那些服务

  • SchedulingPolicyService
  • TelecomLoaderService
  • TelephonyRegistry
  • CameraService
  • AccountManagerService$Lifecycle
  • ContentService$Lifecycle
  • VibratorService
  • ConsumerIrService
  • AlarmManagerService
  • InputManagerService
  • WindowManagerService
  • VrManagerService
  • MetricsLoggerService
  • PinnerService
  • InputMethodManagerService
  • AccessibilityManagerService
  • MountService$Lifecycle
  • UiModeManagerService
  • LockSettingsService$Lifecycle
  • PersistentDataBlockService
  • DeviceIdleController
  • DevicePolicyManagerService
  • StatusBarManagerService
  • ClipboardService
  • NetworkManagementService
  • TextServicesManagerService
  • NetworkScoreService
  • NetworkStatsService
  • NetworkPolicyManagerService
  • WifiNanService
  • WifiP2pService
  • WifiService
  • WifiScanningService
  • RttService
  • EthernetService
  • ConnectivityService
  • NsdService
  • UpdateLockService
  • RecoverySystemService
  • NotificationManagerService
  • DeviceStorageMonitorService
  • LocationManagerService
  • CountryDetectorService
  • SearchManagerService$Lifecycle
  • DropBoxManagerService
  • WallpaperManagerService$Lifecycle
  • AudioService.Lifecycle
  • DockObserver
  • ThermalObserver
  • MidiService$Lifecycle
  • UsbService$Lifecycle
  • SerialService
  • HardwarePropertiesManagerService
  • TwilightService
  • JobSchedulerService
  • SoundTriggerService
  • BackupManagerService$Lifecycle
  • AppWidgetService
  • VoiceInteractionManagerService
  • GestureLauncherService
  • SensorNotificationService
  • ContextHubSystemService
  • DiskStatsService
  • SamplingProfilerService
  • NetworkTimeUpdateService
  • CommonTimeManagementService
  • DreamManagerService
  • AssetAtlasService
  • GraphicsStatsService
  • PrintManagerService
  • RestrictionsManagerService
  • MediaSessionService
  • HdmiControlService
  • TvInputManagerService
  • MediaResourceMonitorService
  • TvRemoteService
  • MediaRouterService
  • TrustManagerService
  • FingerprintService
  • ShortcutService.Lifecycle
  • LauncherAppsService
  • MediaProjectionManagerService
  • WearBluetoothService
  • MmsServiceBroker

所列的这些服务，不一定全部都启动，系统会依照一些配置，选择性启动某些服务。如，因为Android系统会用于众多设备，手机，电视等等，当Android安装到电视设备是，TvInputManagerService、TvRemoteService这些service才会被启动，相反，手机设备时，这两个服务就不会被启动了。

2.不同的启动服务的方式

不知读者是否注意到，在startOtherServices()中存在和startBootstrapServices()、startCoreServices()中不同的启动service的方法，在startBootstrapServices()、startCoreServices()中见到SystemServiceManager.startService()和LocalServices.addService()的方式，而startOtherServices()中又多了ServiceManager.addService()，这三种方式有什么不同呢？

  1. 类型不同
    SystemServiceManager.startService()和LocalServices.addService()启动的系统服务是SystemService的子类，启动这些服务后会回调SystemService的onStart()方法。ServiceManager.addService()启动的系统服务是实现了Android IPC 的Binder的子类，这些服务启动后会调用systemReady()或systemRunning()方法。

  2. SystemServiceManager.startService()和ServiceManager.addService()中启动的服务需要Binder对象，而LocalServices.addService()却没有Binder对象。

  3. SystemServiceManager.startService()中启动的是需要关心lifecycle events的服务，而ServiceManager.addService()和LocalServices.addService()不关心lifecycle events。

  4. ServiceManager.addService()启动的服务本身是实现Binder通信的子类，而一般SystemServiceManager.startService()启动的服务是某个服务的内部类且这个内部类是SystemService的子类，如BackupManagerService$Lifecycle，在启动这个Lifecycle的内部类服务时，当回调onStart()方法时通过SystemService的publishBinderService()方法应用某个服务的Binder对象，且这个Binder的实现类也是某个服务的内部类。也就是说需要启动服务，而这个服务需要关心lifecycle events，所以不能通过ServiceManager.addService()的方式启动，然后在这个服务中声明一个实现了SystemService的子类Lifecycle，来接受lifecycle events，通过SystemServiceManager.startService()的方式启动这个服务，在SystemService的回调方法onStart()中应用这个服务的Binder对象。所以通过SystemServiceManager.startService()启动的服务，实际是启动了一个即需要关心lifecycle events，也需要像ServiceManager.addService()那样需要Binder对象的服务。

所以，其实在startBootstrapServices()中就已经通过ServiceManager.addService()的方式启动了一些特别特别重要的服务，如：

    private void startBootstrapServices() {
        mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
            mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
    }

    public static PackageManagerService main(Context context, Installer installer,
        boolean factoryTest, boolean onlyCore) {
        ......
        ServiceManager.addService("package", m);
        return m;
    }

3.通过ServiceManager.addService()启动的服务，会调用服务的systemReady()或systemRunning()方法，初始化一些需要在系统服务启动后的其它代码。如启动SystemUI。

全部启动所需要的服务以后，SystemServer便要进入了接受Message的循环中，等待Message的事件。

总结

在本大纲中，认识了Android系统启动时需要启动的服务，以及

  • SystemServiceManager.startService()
  • ServiceManager.addService()
  • LocalServices.addService()

三种不同的启动系统服务的方式，通过这三种启动的服务各有什么不同。另外，Android系统除了在启动的时候可以初始化服务，在运行中，也可能有新的服务被加进来，如某些APP启动时，会增加一些服务，如Phone APP（Telephony）

public void onCreate() {
        phoneMgr = PhoneInterfaceManager.init(this, PhoneFactory.getDefaultPhone());
}

static PhoneInterfaceManager init(PhoneGlobals app, Phone phone) {
    synchronized (PhoneInterfaceManager.class) {
        if (sInstance == null) {
            sInstance = new PhoneInterfaceManager(app, phone);
        ......
        return sInstance;
    }
}

private PhoneInterfaceManager(PhoneGlobals app, Phone phone) {
    publish();
}

private void publish() {
    ServiceManager.addService("phone", this);
}

到此，System Server的大纲介绍到这里，在本大纲的牵引下，一一以分文章（文档）的形式对各个系统服务进入全面的了解。

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