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SystemServer启动服务

一、启动流程

SystemServer的在Android体系中所处的地位，SystemServer由Zygote fork生成的，进程名为system_server，该进程承载着framework的核心服务。startSystemServer()函数是system_server启动流程的起点，启动流程图如下：

system_server_boot_process

上图前4步骤（即颜色为紫色的流程）运行在是Zygote进程，从第5步（即颜色为蓝色的流程）ZygoteInit.handleSystemServerProcess开始是运行在新创建的system_server，这是fork机制实现的。

1. startSystemServer

[–>ZygoteInit.java]

private static boolean startSystemServer(String abiList, String socketName) throws MethodAndArgsCaller, RuntimeException {
    ...
    //参数准备
    String args[] = {
        "--setuid=1000",
        "--setgid=1000",
        "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1032,3001,3002,3003,3006,3007",
        "--capabilities=" + capabilities + "," + capabilities,
        "--nice-name=system_server",
        "--runtime-args",
        "com.android.server.SystemServer",
    };

    ZygoteConnection.Arguments parsedArgs = null;
    int pid;
    try {
        //用于解析参数，生成目标格式
        parsedArgs = new ZygoteConnection.Arguments(args);
        ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
        ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);

        // fork子进程，该进程是system_server进程
        pid = Zygote.forkSystemServer(
                parsedArgs.uid, parsedArgs.gid,
                parsedArgs.gids,
                parsedArgs.debugFlags,
                null,
                parsedArgs.permittedCapabilities,
                parsedArgs.effectiveCapabilities);
    } catch (IllegalArgumentException ex) {
        throw new RuntimeException(ex);
    }

    //进入子进程system_server
    if (pid == 0) {
        if (hasSecondZygote(abiList)) {
            waitForSecondaryZygote(socketName);
        }
        // 完成system_server进程剩余的工作 
        handleSystemServerProcess(parsedArgs);
    }
    return true;
}

准备参数并fork新进程，从上面可以看出system server进程参数信息为uid=1000,gid=1000,进程名为sytem_server，从zygote进程fork新进程后，需要关闭zygote原有的socket。

2 forkSystemServer

[–>Zygote.java]

public static int forkSystemServer(int uid, int gid, int[] gids, int debugFlags, int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
    VM_HOOKS.preFork();
    // 调用native方法fork system_server进程
    int pid = nativeForkSystemServer(
            uid, gid, gids, debugFlags, rlimits, permittedCapabilities, effectiveCapabilities);
    if (pid == 0) {
        Trace.setTracingEnabled(true);
    }
    VM_HOOKS.postForkCommon();
    return pid;
}

3. handleSystemServerProcess

[–>ZygoteInit.java]

private static void handleSystemServerProcess( ZygoteConnection.Arguments parsedArgs) throws ZygoteInit.MethodAndArgsCaller {

    closeServerSocket(); //关闭父进程zygote复制而来的Socket//system_server故进入此分支
    RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
}

4. `zygoteInit`

[–>RuntimeInit.java]

public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) throws ZygoteInit.MethodAndArgsCaller {

    nativeZygoteInit(); // zygote初始化 
    applicationInit(targetSdkVersion, argv, classLoader); // 应用初始化
}

5. applicationInit

[–>RuntimeInit.java]

private static void applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) throws ZygoteInit.MethodAndArgsCaller {//调用startClass的static方法 main() 
    invokeStaticMain(args.startClass, args.startArgs, classLoader);
}

此处args.startClass为”com.android.server.SystemServer”。

6. invokeStaticMain

[–>RuntimeInit.java]

private static void invokeStaticMain(String className, String[] argv, ClassLoader classLoader) throws ZygoteInit.MethodAndArgsCaller {
    Class<?> cl = Class.forName(className, true, classLoader);
    ...
    Method m;
    try {
        m = cl.getMethod("main", new Class[] { String[].class });
    } catch (NoSuchMethodException ex) {
        ...
    } catch (SecurityException ex) {
        ...
    }
    int modifiers = m.getModifiers();
    if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
        ...
    }
    //通过抛出异常，回到ZygoteInit.main()。这样做好处是能清空栈帧，提高栈帧利用率。
    throw new ZygoteInit.MethodAndArgsCaller(m, argv);
}

7. MethodAndArgsCaller

[–>ZygoteInit.java]

public static void main(String argv[]) {
    try {
        startSystemServer(abiList, socketName);//启动system_server
        ....
    } catch (MethodAndArgsCaller caller) {
        caller.run(); 
    } catch (RuntimeException ex) {
        closeServerSocket();
        throw ex;
    }
}

invokeStaticMain()方法中抛出的异常MethodAndArgsCaller，从而进入caller.run()方法。

[–>ZygoteInit.java]

public static class MethodAndArgsCaller extends Exception implements Runnable {
    public void run() {
        try {
            //根据传递过来的参数，可知此处通过反射机制调用的是SystemServer.main()方法
            mMethod.invoke(null, new Object[] { mArgs });
        } catch (IllegalAccessException ex) {
            throw new RuntimeException(ex);
        } catch (InvocationTargetException ex) {
            Throwable cause = ex.getCause();
            if (cause instanceof RuntimeException) {
                throw (RuntimeException) cause;
            } else if (cause instanceof Error) {
                throw (Error) cause;
            }
            throw new RuntimeException(ex);}
    }
}

二. SystemServer启动服务

　　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();

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
        new SystemServer().run();
    }
}

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);
    }//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
    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
        startCoreServices();      // 启动核心服务
        startOtherServices();     // 启动其他服务
    } catch (Throwable ex) {
        Slog.e("System", "************ Failure starting system services", ex);
        throw ex;
    }
//一直循环执行
    Looper.loop();
    throw new RuntimeException("Main thread loop unexpectedly exited");
}

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);
}

createSystemContext()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

   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(...);
        
        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()，ActivityManagerService启动过程。

到此, System_server主线程的启动工作完成, 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.

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原文地址：https://www.cnblogs.com/lufeibin/p/13536054.html

SystemServer启动服务

一、启动流程

1. startSystemServer

2 forkSystemServer

3. handleSystemServerProcess

4. zygoteInit

5. applicationInit

6. invokeStaticMain

7. MethodAndArgsCaller

二. SystemServer启动服务

1. SystemServer.main

2. SystemServer.run

1.3 createSystemContext

1.4 startBootstrapServices

1.5 startCoreServices

1.6 startOtherServices

4. `zygoteInit`