Android系统启动-SystemServer下篇-1

基于Android 6.0，在Android 12 上文件状态：

frameworks/base/services/java/com/android/server/
  - SystemServer.java

frameworks/base/services/core/java/com/android/server/
  - SystemServiceManager.java
  - ServiceThread.java
  - am/ActivityManagerService.java

frameworks/base/core/java/android/app/
  - ActivityThread.java
  - LoadedApk.java
  - ContextImpl.java

一、SystemServer启动

上篇文章《Android系统启动-systemServer上篇》从 Zygote 一路启动到 SystemServer 的过程。简单回顾下，在 RuntimeInit.java 中 invokeStaticMain 方法通过创建并抛出异常 ZygoteInit.MethodAndArgsCaller，在 ZygoteInit.java 中的 main() 方法会捕捉该异常，并调用 caller.run()，再通过反射便会调用到 SystemServer.main() 方法，该方法主要执行流程：

SystemServer.main
    SystemServer.run
        createSystemContext
        startBootstrapServices();
        startCoreServices();
        startOtherServices();
        Looper.loop();

接下来，从其 main 方法说起。

1.1 SystemServer.main

public final class SystemServer {
    ...
    public static void main(String[] args) {
        //先初始化SystemServer对象，再调用对象的run()方法，【见小节1.2】
        new SystemServer().run();
    }
}

1.2 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.so
    SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());

    if (SamplingProfilerIntegration.isEnabled()) {
        ...
    }

    //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[见小节1.2.1]
    performPendingShutdown();

    //初始化系统上下文 【见小节1.3】
    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【见小节1.4】
        startCoreServices();      // 启动核心服务【见小节1.5】
        startOtherServices();     // 启动其他服务【见小节1.6】
    } 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。

1.2.1 performPendingShutdown

[–>SystemServer.java]

private void performPendingShutdown() {
    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;
        }
        // 当"sys.shutdown.requested"值不为空,则会重启或者关机
        ShutdownThread.rebootOrShutdown(null, reboot, reason);
    }
}

1.3 createSystemContext

[–>SystemServer.java]

private void createSystemContext() {
    //创建system_server进程的上下文信息
    ActivityThread activityThread = ActivityThread.systemMain();
    mSystemContext = activityThread.getSystemContext();
    //设置主题
    mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);
}

《理解Application创建过程》已介绍过 createSystemContext() 过程，该过程会创建对象有 ActivityThread，Instrumentation, ContextImpl，LoadedApk，Application。

1.4 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);

    //Phase100: 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();
}

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

1.5 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WebViewUpdateService
    mSystemServiceManager.startService(WebViewUpdateService.class);
}

启动服务 BatteryService，UsageStatsService，WebViewUpdateService。

1.6 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，这里就不具体列举源码了，在第四节直接对其中的服务进行一个简单分类。

private void startOtherServices() {
    ...
    SystemConfig.getInstance();
    mContentResolver = context.getContentResolver(); //resolver
    ...
    mActivityManagerService.installSystemProviders(); //provider
    mSystemServiceManager.startService(AlarmManagerService.class); //alarm
    // watchdog
    watchdog.init(context, mActivityManagerService); 
    inputManager = new InputManagerService(context); // input
    wm = WindowManagerService.main(...); // window
    inputManager.start();  //启动input
    mDisplayManagerService.windowManagerAndInputReady();
    ...
    mSystemServiceManager.startService(MOUNT_SERVICE_CLASS); //mount
    mPackageManagerService.performBootDexOpt();  // dexopt操作
    ActivityManagerNative.getDefault().showBootMessage(...); //显示启动界面
    ...
    statusBar = new StatusBarManagerService(context, wm); //statusBar
    //dropbox
    ServiceManager.addService(Context.DROPBOX_SERVICE,
                new DropBoxManagerService(context, new File("/data/system/dropbox")));
     mSystemServiceManager.startService(JobSchedulerService.class); //JobScheduler
     lockSettings.systemReady(); //lockSettings

    //phase480 和phase500
    mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
    mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);
    ...
    // 准备好window, power, package, display服务
    wm.systemReady();
    mPowerManagerService.systemReady(...);
    mPackageManagerService.systemReady();
    mDisplayManagerService.systemReady(...);
    
    //重头戏[见小节2.1]
    mActivityManagerService.systemReady(new Runnable() {
        public void run() {
          ...
        }
    });
}

SystemServer启动各种服务中最后的一个环节便是AMS.systemReady()，详见《ActivityManagerService启动过程》.

到此, System_server 主线程的启动工作总算完成, 进入 Looper.loop() 状态,等待其他线程通过 handler 发送消息到主线再处理.

二、服务启动阶段

SystemServiceManager 的 startBootPhase() 贯穿 system_server 进程的整个启动过程：

其中 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。

各个启动阶段所在源码的大致位置：

public final class SystemServer {

    private void startBootstrapServices() {
      ...
      //phase100
      mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
      ...
    }

    private void startCoreServices() {
      ...
    }

    private void startOtherServices() {
      ...
      //phase480 && 500
      mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
      mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);
      
      ...
      mActivityManagerService.systemReady(new Runnable() {
         public void run() {
             //phase550
             mSystemServiceManager.startBootPhase(
                     SystemService.PHASE_ACTIVITY_MANAGER_READY);
             ...
             //phase600
             mSystemServiceManager.startBootPhase(
                     SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
          }
      }
    }
}

接下来再说说简单每个阶段的大概完成的工作：

2.1 Phase0

创建四大引导服务:

ActivityManagerService
PowerManagerService
LightsService
DisplayManagerService

2.2 Phase100

进入阶段 PHASE_WAIT_FOR_DEFAULT_DISPLAY=100 回调服务

onBootPhase(100)
    DisplayManagerService
//然后创建大量服务下面列举部分:
    PackageManagerService
    WindowManagerService
    InputManagerService
    NetworkManagerService
    DropBoxManagerService
    FingerprintService
    LauncherAppsService
    …

2.3 Phase480

进入阶段 PHASE_LOCK_SETTINGS_READY=480 回调服务

onBootPhase(480)
    DevicePolicyManagerService

阶段480后马上就进入阶段500.

2.4 Phase500

PHASE_SYSTEM_SERVICES_READY=500，进入该阶段服务能安全地调用核心系统服务.

onBootPhase(500)
    AlarmManagerService
    JobSchedulerService
    NotificationManagerService
    BackupManagerService
    UsageStatsService
    DeviceIdleController
    TrustManagerService
    UiModeManagerService

    BluetoothService
    BluetoothManagerService
    EthernetService
    WifiP2pService
    WifiScanningService
    WifiService
    RttService

各大服务执行 systemReady():

WindowManagerService.systemReady():
PowerManagerService.systemReady():
PackageManagerService.systemReady():
DisplayManagerService.systemReady():

接下来就绪 AMS.systemReady 方法.

2.5 Phase550

PHASE_ACTIVITY_MANAGER_READY=550， AMS.mSystemReady=true, 已准备就绪，进入该阶段服务能广播Intent;但是 system_server 主线程并没有就绪.

onBootPhase(550)
    MountService
    TelecomLoaderService
    UsbService
    WebViewUpdateService
    DockObserver
    BatteryService

接下来执行: (AMS启动native crash监控, 加载WebView，启动SystemUi等),如下：

mActivityManagerService.startObservingNativeCrashes();
WebViewFactory.prepareWebViewInSystemServer();
startSystemUi(context);

networkScoreF.systemReady();
networkManagementF.systemReady();
networkStatsF.systemReady();
networkPolicyF.systemReady();
connectivityF.systemReady();
audioServiceF.systemReady();
Watchdog.getInstance().start();

2.6 Phase600

PHASE_THIRD_PARTY_APPS_CAN_START=600

onBootPhase(600)
    JobSchedulerService
    NotificationManagerService
    BackupManagerService
    AppWidgetService
    GestureLauncherService
    DreamManagerService
    TrustManagerService
    VoiceInteractionManagerService

接下来,各种服务的 systemRunning() 过程:

WallpaperManagerService
InputMethodManagerService
LocationManagerService
CountryDetectorService
NetworkTimeUpdateService
CommonTimeManagementService
TextServicesManagerService
AssetAtlasService
InputManagerService
TelephonyRegistry
MediaRouterService
MmsServiceBroker

这些服务依次执行其 systemRunning()方法。

2.7 Phase1000

在经过一系列流程，再调用 AMS.finishBooting() 时，则进入阶段 Phase1000。

到此，系统服务启动阶段完成就绪，system_server 进程启动完成则进入 Looper.loop()状态，随时待命，等待消息队列 MessageQueue 中的消息到来，则马上进入执行状态。

三、服务类别

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。以下这些系统服务的注册过程, 见《Android系统服务的注册方式》

引导服务(7个)：ActivityManagerService、PowerManagerService、LightsService、DisplayManagerService、PackageManagerService、UserManagerService、SensorService；
核心服务(3个)：BatteryService、UsageStatsService、WebViewUpdateService；
其他服务(70个+)：AlarmManagerService、VibratorService等。合计总大约80个系统服务：

`ActivityManagerService`	`PackageManagerService`	`WindowManagerService`
`PowerManagerService`	`BatteryService`	`BatteryStatsService`
`DreamManagerService`	`DropBoxManagerService`	`SamplingProfilerService`
`UsageStatsService`	`DiskStatsService`	`DeviceStorageMonitorService`
SchedulingPolicyService	`AlarmManagerService`	DeviceIdleController
ThermalObserver	JobSchedulerService	`AccessibilityManagerService`
DisplayManagerService	LightsService	`GraphicsStatsService`
StatusBarManagerService	NotificationManagerService	WallpaperManagerService
UiModeManagerService	AppWidgetService	LauncherAppsService
TextServicesManagerService	ContentService	LockSettingsService
InputMethodManagerService	InputManagerService	`MountService`
FingerprintService	TvInputManagerService	DockObserver
NetworkManagementService	NetworkScoreService	`NetworkStatsService`
NetworkPolicyManagerService	ConnectivityService	BluetoothService
WifiP2pService	WifiService	WifiScanningService
AudioService	MediaRouterService	VoiceInteractionManagerService
MediaProjectionManagerService	MediaSessionService
DevicePolicyManagerService	PrintManagerService	`BackupManagerService`
`UserManagerService`	AccountManagerService	`TrustManagerService`
`SensorService`	LocationManagerService	VibratorService
CountryDetectorService	GestureLauncherService	PersistentDataBlockService
EthernetService	WebViewUpdateService	ClipboardService
TelephonyRegistry	TelecomLoaderService	NsdService
UpdateLockService	SerialService	SearchManagerService
CommonTimeManagementService	AssetAtlasService	ConsumerIrService
MidiServiceCameraService	TwilightService	RestrictionsManagerService
MmsServiceBroker	RttService	UsbService

四、补充

1. SystemServer中通过判断 Build.IS_DEBUGGABLE 来判断是否是debug版本。

2. 特征函数调用位置

onStart() --> publishBinderServices() //SensorService.java
onBootPhase(int phase) //SensorService.java 服务内只在指定启动阶段进行响应
startOtherServices() --> wm.systemReady() //SystemServer.java

3. 这个属性指示使用哪个库

/ # getprop | grep persist.sys.dalvik.vm.lib.2
[persist.sys.dalvik.vm.lib.2]: [libart.so]

参考：

Android系统启动-SystemServer下篇: http://gityuan.com/2016/02/20/android-system-server-2/

posted on 2023-08-14 15:27 Hello-World3 阅读(180) 评论(0) 编辑收藏举报

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