05 Android系统启动-SystemServer下篇

作者: 凤邪摩羯 | 来源:发表于2020-09-29 09:55 被阅读0次

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

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：

system_server服务启动流程

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：

05 Android系统启动-SystemServer下篇

一. SystemServer启动

1.1 SystemServer.main

1.2 SystemServer.run

1.2.1 performPendingShutdown

1.3 createSystemContext

1.4 startBootstrapServices

1.5 startCoreServices

1.6 startOtherServices

二、服务启动阶段

2.1 Phase0

2.2 Phase100

2.3 Phase480

2.4 Phase500

2.5 Phase550

2.6 Phase600

2.7 Phase1000

三、服务类别

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