相关源码路径

/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java/frameworks/base/core/services/java/com/android/server/SystemServer.java/frameworks/base/core/java/com/android/internal/os/Zygote.java/frameworks/base/core/jni/com_android_internal_os_Zygote.cpp/frameworks/base/cmds/app_process/App_main.cpp （内含AppRuntime类）/frameworks/base/core/jni/AndroidRuntime.cppframeworks/base/core/java/android/app/ActivityThread.javaframeworks/base/core/java/android/app/LoadedApk.javaframeworks/base/core/java/android/app/ContextImpl.javaframeworks/base/core/java/com/android/server/LocalServices.javaframeworks/base/services/java/com/android/server/SystemServer.javaframeworks/base/services/core/java/com/android/server/SystemServiceManager.javaframeworks/base/services/core/java/com/android/server/ServiceThread.javaframeworks/base/services/core/java/com/android/server/pm/Installer.javaframeworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

 /**     * Prepare the arguments and fork for the system server process.     */    private static boolean startSystemServer(String abiList, String socketName)            throws MethodAndArgsCaller, RuntimeException {        long capabilities = posixCapabilitiesAsBits(            OsConstants.CAP_BLOCK_SUSPEND,            OsConstants.CAP_KILL,            OsConstants.CAP_NET_ADMIN,            OsConstants.CAP_NET_BIND_SERVICE,            OsConstants.CAP_NET_BROADCAST,            OsConstants.CAP_NET_RAW,            OsConstants.CAP_SYS_MODULE,            OsConstants.CAP_SYS_NICE,            OsConstants.CAP_SYS_RESOURCE,            OsConstants.CAP_SYS_TIME,            OsConstants.CAP_SYS_TTY_CONFIG        );        /* Hardcoded command line to start the system server */        String args[] = {            "--setuid=1000",            "--setgid=1000",            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1032,3001,3002,3003,3006,3007",            "--capabilities=" + capabilities + "," + capabilities,            "--runtime-init",            "--nice-name=system_server",            "com.android.server.SystemServer",        };        ZygoteConnection.Arguments parsedArgs = null;        int pid;        try {            parsedArgs = new ZygoteConnection.Arguments(args);            ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);            ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);            /* Request to fork the system server process */            pid = Zygote.forkSystemServer(                    parsedArgs.uid, parsedArgs.gid,                    parsedArgs.gids,                    parsedArgs.debugFlags,                    null,                    parsedArgs.permittedCapabilities,                    parsedArgs.effectiveCapabilities);        } catch (IllegalArgumentException ex) {            throw new RuntimeException(ex);        }        /* For child process */        if (pid == 0) {            if (hasSecondZygote(abiList)) {                waitForSecondaryZygote(socketName);            }            handleSystemServerProcess(parsedArgs);        }        return true;    }

       （2）调用forkSystemServer()从当前的zygote进程孵化出新的进程。该函数是一个native函数，其作用与folkAndSpecilize()相似；

       （3）第三处，新进程启动后。在handleSystemServerProcess()函数中主要完成两件事情，第一是关闭Socket服务端，第二是抛出异常MethodAndArgsCaller，通过caller.run()启动com.android.server.SystemServer的main 方法。调用类如下：

startSystemServer     Zygote.forkSystemServer     handleSystemServerProcess           closeServerSocket           RuntimeInit.zygoteInit                   applicationInit                          invokeStaticMain                                 throw new ZygoteInit.MethodAndArgsCaller

一、启动流程

         startSystemServer()函数是system_server启动流程的起点，启动流程图如下：

         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（fork会返回2次）。

二、SystemServer.main()

调用栈：

SystemServer.main      SystemServer.run          createSystemContext              ActivityThread.systemMain                  ActivityThread.attach                      LoadedApk.makeApplication              ActivityThread.getSystemContext                  ContextImpl.createSystemContext          startBootstrapServices();          startCoreServices();          startOtherServices();          Looper.loop();  

流程图：

源码：

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

private void run() {          // 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.          if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {              Slog.w(TAG, "System clock is before 1970; setting to 1970.");              SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);          } // 检测时间设置            // Here we go!          Slog.i(TAG, "Entered the Android system server!");          EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, SystemClock.uptimeMillis());            // In case the runtime switched since last boot (such as when          // the old runtime was removed in an OTA), set the system          // property so that it is in sync. We can't do this in          // libnativehelper's JniInvocation::Init code where we already          // had to fallback to a different runtime because it is          // running as root and we need to be the system user to set          // the property. http://b/11463182          SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());            // Enable the sampling profiler.          if (SamplingProfilerIntegration.isEnabled()) {              SamplingProfilerIntegration.start();              mProfilerSnapshotTimer = new Timer();              mProfilerSnapshotTimer.schedule(new TimerTask() {                  @Override                  public void run() {                      SamplingProfilerIntegration.writeSnapshot("system_server", null);                  }              }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);          } // 启动性能分析采样            // Mmmmmm... more memory!          VMRuntime.getRuntime().clearGrowthLimit();            // 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);            // Some devices rely on runtime fingerprint generation, so make sure          // we've defined it before booting further.          Build.ensureFingerprintProperty();            // Within the system server, it is an error to access Environment paths without          // explicitly specifying a user.          Environment.setUserRequired(true);            // Ensure binder calls into the system always run at foreground priority.          BinderInternal.disableBackgroundScheduling(true);            // Prepare the main looper thread (this thread).          android.os.Process.setThreadPriority(                  android.os.Process.THREAD_PRIORITY_FOREGROUND);          android.os.Process.setCanSelfBackground(false);          Looper.prepareMainLooper(); // 准备主线程循环            // Initialize native services.          System.loadLibrary("android_servers");          nativeInit();            // Check whether we failed to shut down last time we tried.          // This call may not return.          performPendingShutdown();            // Initialize the system context.          createSystemContext();            // Create the system service manager.          mSystemServiceManager = new SystemServiceManager(mSystemContext);          LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);            // Start services.  // 启动服务          try {              startBootstrapServices();              startCoreServices();              startOtherServices();          } catch (Throwable ex) {              Slog.e("System", "******************************************");              Slog.e("System", "************ Failure starting system services", ex);              throw ex;          }            // For debug builds, log event loop stalls to dropbox for analysis.          if (StrictMode.conditionallyEnableDebugLogging()) {              Slog.i(TAG, "Enabled StrictMode for system server main thread.");          }            // Loop forever.          Looper.loop();  // 启动线程循环，等待消息处理          throw new RuntimeException("Main thread loop unexpectedly exited");      }  

private void createSystemContext() {      ActivityThread activityThread = ActivityThread.systemMain();      mSystemContext = activityThread.getSystemContext();      mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);  }  

ActivityThread.systemMain

        ActivityThread.attach 

        ActivityThread.getSystemContext    

 ActivityThread.attach ：主要工作是创建应用上下文ContextImpl，创建Application以及调用其onCreate()方法，设置DropBox以及ComponentCallbacks2回调方法。

public static ActivityThread systemMain() {    // The system process on low-memory devices do not get to use hardware    // accelerated drawing, since this can add too much overhead to the    // process.    if (!ActivityManager.isHighEndGfx()) {        HardwareRenderer.disable(true);    } else {        HardwareRenderer.enableForegroundTrimming();    }    ActivityThread thread = new ActivityThread();    thread.attach(true);    return thread;}

创建一个ActivityThread，并调用其attath方法。

private void attach(boolean system) {    sCurrentActivityThread = this;    mSystemThread = system;    if (!system) {        ......        ......        // 省略部分代码    } else {        android.ddm.DdmHandleAppName.setAppName("system_process",                UserHandle.myUserId());        try {            mInstrumentation = new Instrumentation();            ContextImpl context = ContextImpl.createAppContext(                    this, getSystemContext().mPackageInfo);            mInitialApplication = context.mPackageInfo.makeApplication(true, null);            mInitialApplication.onCreate();        } catch (Exception e) {            throw new RuntimeException(                    "Unable to instantiate Application():" + e.toString(), e);        }    }    // add dropbox logging to libcore    DropBox.setReporter(new DropBoxReporter());    ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {        @Override        public void onConfigurationChanged(Configuration newConfig) {            synchronized (mResourcesManager) {                // We need to apply this change to the resources                // immediately, because upon returning the view                // hierarchy will be informed about it.                if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) {                    // This actually changed the resources!  Tell                    // everyone about it.                    if (mPendingConfiguration == null ||                            mPendingConfiguration.isOtherSeqNewer(newConfig)) {                        mPendingConfiguration = newConfig;                        sendMessage(H.CONFIGURATION_CHANGED, newConfig);                    }                }            }        }        @Override        public void onLowMemory() {        }        @Override        public void onTrimMemory(int level) {        }    });}

（2）startBootstrapServices()

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);    //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();}

【system_server中启动的服务介绍】

system_server进程中的服务启动方式有两种，分别是SystemServiceManager的startService()和ServiceManager的addService

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);}

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 final class ActivityManagerService extends ActivityManagerNative    implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {            public void systemReady(final Runnable goingCallback) {        ... //update相关        mSystemReady = true;                //杀掉所有非persistent进程        removeProcessLocked(proc, true, false, "system update done");        mProcessesReady = true;         goingCallback.run();                  addAppLocked(info, false, null); //启动所有的persistent进程        mBooting = true;                 //启动home        startHomeActivityLocked(mCurrentUserId, "systemReady");         //恢复栈顶的Activity        mStackSupervisor.resumeTopActivitiesLocked();    }}