Android的System Server

System Server是Android系统的核心，他在Dalvik虚拟机启动后立即开始初始化和运行。其它的系统服务在System Server进程的环境中运行。/base/services/java/com/android/server/SystemServer.java

    /**     * This method is called from Zygote to initialize the system. This will cause the native     * services (SurfaceFlinger, AudioFlinger, etc..) to be started. After that it will call back     * up into init2() to start the Android services.     */    native public static void init1(String[] args);    public static void main(String[] args) {        if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {            // 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.            Slog.w(TAG, "System clock is before 1970; setting to 1970.");            SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);        }        if (SamplingProfilerIntegration.isEnabled()) {            SamplingProfilerIntegration.start();            timer = new Timer();            timer.schedule(new TimerTask() {                @Override                public void run() {                    SamplingProfilerIntegration.writeSnapshot("system_server");                }            }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);        }        // 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);                System.loadLibrary("android_servers");        init1(args);    }    public static final void init2() {        Slog.i(TAG, "Entered the Android system server!");        Thread thr = new ServerThread();        thr.setName("android.server.ServerThread");        thr.start();    }

在main函数中，首先检查系统时间设置和SamplingProfiler。然后加载一个叫android_servers的本地库，他提供本地方法的接口（源程序在framework/base/services/jni/目录中）。然后调用本地方法设置服务。具体执行设置的代码在frameworks/base/cmds/system_server/library/system_init.cpp中。

extern "C" status_t system_init(){    LOGI("Entered system_init()");        sp<ProcessState> proc(ProcessState::self());        sp<IServiceManager> sm = defaultServiceManager();    LOGI("ServiceManager: %p\n", sm.get());        sp<GrimReaper> grim = new GrimReaper();    sm->asBinder()->linkToDeath(grim, grim.get(), 0);        char propBuf[PROPERTY_VALUE_MAX];    property_get("system_init.startsurfaceflinger", propBuf, "1");    if (strcmp(propBuf, "1") == 0) {        // Start the SurfaceFlinger        SurfaceFlinger::instantiate();    }    // Start the sensor service    SensorService::instantiate();    // On the simulator, audioflinger et al don't get started the    // same way as on the device, and we need to start them here    if (!proc->supportsProcesses()) {        // Start the AudioFlinger        AudioFlinger::instantiate();        // Start the media playback service        MediaPlayerService::instantiate();        // Start the camera service        CameraService::instantiate();        // Start the audio policy service        AudioPolicyService::instantiate();    }    // And now start the Android runtime.  We have to do this bit    // of nastiness because the Android runtime initialization requires    // some of the core system services to already be started.    // All other servers should just start the Android runtime at    // the beginning of their processes's main(), before calling    // the init function.    LOGI("System server: starting Android runtime.\n");        AndroidRuntime* runtime = AndroidRuntime::getRuntime();    LOGI("System server: starting Android services.\n");    runtime->callStatic("com/android/server/SystemServer", "init2");            // If running in our own process, just go into the thread    // pool.  Otherwise, call the initialization finished    // func to let this process continue its initilization.    if (proc->supportsProcesses()) {        LOGI("System server: entering thread pool.\n");        ProcessState::self()->startThreadPool();        IPCThreadState::self()->joinThreadPool();        LOGI("System server: exiting thread pool.\n");    }    return NO_ERROR;}

等初始化传感器，视频，音频等服务后，调用一个回调方法init2 (在SystemServer.java中)。在上面的代码可以看到，这个方法开启了ServerThread来初始化其它的服务。

   public void run() {        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN,            SystemClock.uptimeMillis());        Looper.prepare();        android.os.Process.setThreadPriority(                android.os.Process.THREAD_PRIORITY_FOREGROUND);        BinderInternal.disableBackgroundScheduling(true);        android.os.Process.setCanSelfBackground(false);        // Check whether we failed to shut down last time we tried.        {            final String shutdownAction = SystemProperties.get(                    ShutdownThread.SHUTDOWN_ACTION_PROPERTY, "");            if (shutdownAction != null && shutdownAction.length() > 0) {                boolean reboot = (shutdownAction.charAt(0) == '1');                final String reason;                if (shutdownAction.length() > 1) {                    reason = shutdownAction.substring(1, shutdownAction.length());                } else {                    reason = null;                }                ShutdownThread.rebootOrShutdown(reboot, reason);            }        }        String factoryTestStr = SystemProperties.get("ro.factorytest");        int factoryTest = "".equals(factoryTestStr) ? SystemServer.FACTORY_TEST_OFF                : Integer.parseInt(factoryTestStr);        LightsService lights = null;        PowerManagerService power = null;        BatteryService battery = null;        ConnectivityService connectivity = null;        IPackageManager pm = null;        Context context = null;        WindowManagerService wm = null;        BluetoothService bluetooth = null;        BluetoothA2dpService bluetoothA2dp = null;        HeadsetObserver headset = null;        DockObserver dock = null;        UsbService usb = null;        UiModeManagerService uiMode = null;        RecognitionManagerService recognition = null;        ThrottleService throttle = null;        // Critical services...        try {            Slog.i(TAG, "Entropy Service");            ServiceManager.addService("entropy", new EntropyService());            Slog.i(TAG, "Power Manager");            power = new PowerManagerService();            ServiceManager.addService(Context.POWER_SERVICE, power);            Slog.i(TAG, "Activity Manager");            context = ActivityManagerService.main(factoryTest);            Slog.i(TAG, "Telephony Registry");            ServiceManager.addService("telephony.registry", new TelephonyRegistry(context));            AttributeCache.init(context);            Slog.i(TAG, "Package Manager");            pm = PackageManagerService.main(context,                    factoryTest != SystemServer.FACTORY_TEST_OFF);            ActivityManagerService.setSystemProcess();            mContentResolver = context.getContentResolver();            // The AccountManager must come before the ContentService            try {                Slog.i(TAG, "Account Manager");                ServiceManager.addService(Context.ACCOUNT_SERVICE,                        new AccountManagerService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Account Manager", e);            }            Slog.i(TAG, "Content Manager");            ContentService.main(context,                    factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);            Slog.i(TAG, "System Content Providers");            ActivityManagerService.installSystemProviders();            Slog.i(TAG, "Battery Service");            battery = new BatteryService(context);            ServiceManager.addService("battery", battery);            Slog.i(TAG, "Lights Service");            lights = new LightsService(context);            Slog.i(TAG, "Vibrator Service");            ServiceManager.addService("vibrator", new VibratorService(context));            // only initialize the power service after we have started the            // lights service, content providers and the battery service.            power.init(context, lights, ActivityManagerService.getDefault(), battery);            Slog.i(TAG, "Alarm Manager");            AlarmManagerService alarm = new AlarmManagerService(context);            ServiceManager.addService(Context.ALARM_SERVICE, alarm);            Slog.i(TAG, "Init Watchdog");            Watchdog.getInstance().init(context, battery, power, alarm,                    ActivityManagerService.self());            Slog.i(TAG, "Window Manager");            wm = WindowManagerService.main(context, power,                    factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL);            ServiceManager.addService(Context.WINDOW_SERVICE, wm);            ((ActivityManagerService)ServiceManager.getService("activity"))                    .setWindowManager(wm);            // Skip Bluetooth if we have an emulator kernel            // TODO: Use a more reliable check to see if this product should            // support Bluetooth - see bug 988521            if (SystemProperties.get("ro.kernel.qemu").equals("1")) {                Slog.i(TAG, "Registering null Bluetooth Service (emulator)");                ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, null);            } else if (factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL) {                Slog.i(TAG, "Registering null Bluetooth Service (factory test)");                ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, null);            } else {                Slog.i(TAG, "Bluetooth Service");                bluetooth = new BluetoothService(context);                ServiceManager.addService(BluetoothAdapter.BLUETOOTH_SERVICE, bluetooth);                bluetooth.initAfterRegistration();                bluetoothA2dp = new BluetoothA2dpService(context, bluetooth);                ServiceManager.addService(BluetoothA2dpService.BLUETOOTH_A2DP_SERVICE,                                          bluetoothA2dp);                int bluetoothOn = Settings.Secure.getInt(mContentResolver,                    Settings.Secure.BLUETOOTH_ON, 0);                if (bluetoothOn > 0) {                    bluetooth.enable();                }            }        } catch (RuntimeException e) {            Slog.e("System", "Failure starting core service", e);        }        DevicePolicyManagerService devicePolicy = null;        StatusBarManagerService statusBar = null;        InputMethodManagerService imm = null;        AppWidgetService appWidget = null;        NotificationManagerService notification = null;        WallpaperManagerService wallpaper = null;        LocationManagerService location = null;        if (factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {            try {                Slog.i(TAG, "Device Policy");                devicePolicy = new DevicePolicyManagerService(context);                ServiceManager.addService(Context.DEVICE_POLICY_SERVICE, devicePolicy);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting DevicePolicyService", e);            }            try {                Slog.i(TAG, "Status Bar");                statusBar = new StatusBarManagerService(context);                ServiceManager.addService(Context.STATUS_BAR_SERVICE, statusBar);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting StatusBarManagerService", e);            }            try {                Slog.i(TAG, "Clipboard Service");                ServiceManager.addService(Context.CLIPBOARD_SERVICE,                        new ClipboardService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Clipboard Service", e);            }            try {                Slog.i(TAG, "Input Method Service");                imm = new InputMethodManagerService(context, statusBar);                ServiceManager.addService(Context.INPUT_METHOD_SERVICE, imm);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Input Manager Service", e);            }            try {                Slog.i(TAG, "NetStat Service");                ServiceManager.addService("netstat", new NetStatService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting NetStat Service", e);            }            try {                Slog.i(TAG, "NetworkManagement Service");                ServiceManager.addService(                        Context.NETWORKMANAGEMENT_SERVICE,                        NetworkManagementService.create(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting NetworkManagement Service", e);            }            try {                Slog.i(TAG, "Connectivity Service");                connectivity = ConnectivityService.getInstance(context);                ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Connectivity Service", e);            }            try {                Slog.i(TAG, "Throttle Service");                throttle = new ThrottleService(context);                ServiceManager.addService(                        Context.THROTTLE_SERVICE, throttle);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting ThrottleService", e);            }            try {              Slog.i(TAG, "Accessibility Manager");              ServiceManager.addService(Context.ACCESSIBILITY_SERVICE,                      new AccessibilityManagerService(context));            } catch (Throwable e) {              Slog.e(TAG, "Failure starting Accessibility Manager", e);            }            try {                /*                 * NotificationManagerService is dependant on MountService,                 * (for media / usb notifications) so we must start MountService first.                 */                Slog.i(TAG, "Mount Service");                ServiceManager.addService("mount", new MountService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Mount Service", e);            }            try {                Slog.i(TAG, "Notification Manager");                notification = new NotificationManagerService(context, statusBar, lights);                ServiceManager.addService(Context.NOTIFICATION_SERVICE, notification);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Notification Manager", e);            }            try {                Slog.i(TAG, "Device Storage Monitor");                ServiceManager.addService(DeviceStorageMonitorService.SERVICE,                        new DeviceStorageMonitorService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting DeviceStorageMonitor service", e);            }            try {                Slog.i(TAG, "Location Manager");                location = new LocationManagerService(context);                ServiceManager.addService(Context.LOCATION_SERVICE, location);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Location Manager", e);            }            try {                Slog.i(TAG, "Search Service");                ServiceManager.addService(Context.SEARCH_SERVICE,                        new SearchManagerService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Search Service", e);            }            if (INCLUDE_DEMO) {                Slog.i(TAG, "Installing demo data...");                (new DemoThread(context)).start();            }            try {                Slog.i(TAG, "DropBox Service");                ServiceManager.addService(Context.DROPBOX_SERVICE,                        new DropBoxManagerService(context, new File("/data/system/dropbox")));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting DropBoxManagerService", e);            }            try {                Slog.i(TAG, "Wallpaper Service");                wallpaper = new WallpaperManagerService(context);                ServiceManager.addService(Context.WALLPAPER_SERVICE, wallpaper);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Wallpaper Service", e);            }            try {                Slog.i(TAG, "Audio Service");                ServiceManager.addService(Context.AUDIO_SERVICE, new AudioService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Audio Service", e);            }            try {                Slog.i(TAG, "Headset Observer");                // Listen for wired headset changes                headset = new HeadsetObserver(context);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting HeadsetObserver", e);            }            try {                Slog.i(TAG, "Dock Observer");                // Listen for dock station changes                dock = new DockObserver(context, power);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting DockObserver", e);            }            try {                Slog.i(TAG, "USB Service");                // Listen for USB changes                usb = new UsbService(context);                ServiceManager.addService(Context.USB_SERVICE, usb);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting UsbService", e);            }            try {                Slog.i(TAG, "UI Mode Manager Service");                // Listen for UI mode changes                uiMode = new UiModeManagerService(context);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting UiModeManagerService", e);            }            try {                Slog.i(TAG, "Backup Service");                ServiceManager.addService(Context.BACKUP_SERVICE,                        new BackupManagerService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Backup Service", e);            }            try {                Slog.i(TAG, "AppWidget Service");                appWidget = new AppWidgetService(context);                ServiceManager.addService(Context.APPWIDGET_SERVICE, appWidget);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting AppWidget Service", e);            }            try {                Slog.i(TAG, "Recognition Service");                recognition = new RecognitionManagerService(context);            } catch (Throwable e) {                Slog.e(TAG, "Failure starting Recognition Service", e);            }                        try {                Slog.i(TAG, "DiskStats Service");                ServiceManager.addService("diskstats", new DiskStatsService(context));            } catch (Throwable e) {                Slog.e(TAG, "Failure starting DiskStats Service", e);            }        }        // make sure the ADB_ENABLED setting value matches the secure property value        Settings.Secure.putInt(mContentResolver, Settings.Secure.ADB_ENABLED,                "1".equals(SystemProperties.get("persist.service.adb.enable")) ? 1 : 0);        // register observer to listen for settings changes        mContentResolver.registerContentObserver(Settings.Secure.getUriFor(Settings.Secure.ADB_ENABLED),                false, new AdbSettingsObserver());        // Before things start rolling, be sure we have decided whether        // we are in safe mode.        final boolean safeMode = wm.detectSafeMode();        if (safeMode) {            try {                ActivityManagerNative.getDefault().enterSafeMode();                // Post the safe mode state in the Zygote class                Zygote.systemInSafeMode = true;                // Disable the JIT for the system_server process                VMRuntime.getRuntime().disableJitCompilation();            } catch (RemoteException e) {            }        } else {            // Enable the JIT for the system_server process            VMRuntime.getRuntime().startJitCompilation();        }        // It is now time to start up the app processes...        if (devicePolicy != null) {            devicePolicy.systemReady();        }        if (notification != null) {            notification.systemReady();        }        if (statusBar != null) {            statusBar.systemReady();        }        wm.systemReady();        power.systemReady();        try {            pm.systemReady();        } catch (RemoteException e) {        }        // These are needed to propagate to the runnable below.        final StatusBarManagerService statusBarF = statusBar;        final BatteryService batteryF = battery;        final ConnectivityService connectivityF = connectivity;        final DockObserver dockF = dock;        final UsbService usbF = usb;        final ThrottleService throttleF = throttle;        final UiModeManagerService uiModeF = uiMode;        final AppWidgetService appWidgetF = appWidget;        final WallpaperManagerService wallpaperF = wallpaper;        final InputMethodManagerService immF = imm;        final RecognitionManagerService recognitionF = recognition;        final LocationManagerService locationF = location;        // We now tell the activity manager it is okay to run third party        // code.  It will call back into us once it has gotten to the state        // where third party code can really run (but before it has actually        // started launching the initial applications), for us to complete our        // initialization.        ((ActivityManagerService)ActivityManagerNative.getDefault())                .systemReady(new Runnable() {            public void run() {                Slog.i(TAG, "Making services ready");                if (statusBarF != null) statusBarF.systemReady2();                if (batteryF != null) batteryF.systemReady();                if (connectivityF != null) connectivityF.systemReady();                if (dockF != null) dockF.systemReady();                if (usbF != null) usbF.systemReady();                if (uiModeF != null) uiModeF.systemReady();                if (recognitionF != null) recognitionF.systemReady();                Watchdog.getInstance().start();                // It is now okay to let the various system services start their                // third party code...                if (appWidgetF != null) appWidgetF.systemReady(safeMode);                if (wallpaperF != null) wallpaperF.systemReady();                if (immF != null) immF.systemReady();                if (locationF != null) locationF.systemReady();                if (throttleF != null) throttleF.systemReady();            }        });        // For debug builds, log event loop stalls to dropbox for analysis.        if (StrictMode.conditionallyEnableDebugLogging()) {            Slog.i(TAG, "Enabled StrictMode for system server main thread.");        }        Looper.loop();        Slog.d(TAG, "System ServerThread is exiting!");    }

这里启动的没一个进程都作为一个Dalvik线程而存在于SystemServer进程里面。

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