Android Activity启动流程刨析

 /**
    * The main entry point from zygote.
    */
   public static void main(String[] args) {
       new SystemServer().run();
   }

 private void startBootstrapServices() {
       ......
       //启动AMS服务
       Installer installer = mSystemServiceManager.startService(Installer.class);
       //请注意这里参数是Lifecycle，因为AMS是在Lifecycle里面new出来的
       mActivityManagerService = mSystemServiceManager.startService(
               ActivityManagerService.Lifecycle.class).getService();
       mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
       mActivityManagerService.setInstaller(installer);
       mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
       mActivityManagerService.initPowerManagement();
        ......
       mActivityManagerService.setSystemProcess();
     ......
}

 public SystemService startService(String className) {
       final Class<SystemService> serviceClass;
       try {
           serviceClass = (Class<SystemService>)Class.forName(className);
       } catch (ClassNotFoundException ex) {
           Slog.i(TAG, "Starting "   className);
       }
       return startService(serviceClass);
   }

public <T extends SystemService> T startService(Class<T> serviceClass) {
       try {
           final String name = serviceClass.getName();
           // 1、创建服务
           final T service;
           try {
               Constructor<T> constructor = serviceClass.getConstructor(Context.class);
             // 如果传进来的是ActivityManagerService.Lifecycle对象，那么ActivityManagerService就能被创建
               service = constructor.newInstance(mContext);
           } catch (InstantiationException ex) {
               throw new RuntimeException("Failed to create service "   name
                         ": service could not be instantiated", ex);
           }
           // 2、注册服务
           mServices.add(service);

           // 3、启动服务
           try {
               service.onStart();
           } catch (RuntimeException ex) {
               throw new RuntimeException("Failed to start service "   name
                         ": onStart threw an exception", ex);
           }
           return service;
       } finally {
           Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
       }
   }

ActivityManagerService.java
  public static final class Lifecycle extends SystemService {
       private final ActivityManagerService mService;
       public Lifecycle(Context context) {
           super(context);
         //ActivityManagerService被new出来了
           mService = new ActivityManagerService(context);
       }
       @Override
       public void onStart() {
         //  启动
           mService.start();
       }
       public ActivityManagerService getService() {
           return mService;
       }
   }

 private void start() {
       Process.removeAllProcessGroups();
       mProcessCpuThread.start();
       mBatteryStatsService.publish(mContext);
       mAppOpsService.publish(mContext);
       Slog.d("AppOps", "AppOpsService published");
       LocalServices.addService(ActivityManagerInternal.class, new LocalService());
   }

public void setSystemProcess() {
       try {
           ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
           ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
           ServiceManager.addService("meminfo", new MemBinder(this));
           ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
           ServiceManager.addService("dbinfo", new DbBinder(this));
           ......
      // 设置application info LoadedApkinfo 有关 framework-res.apk
       ApplicationInfo info = mContext.getPackageManager().getApplicationInfo( "android", STOCK_PM_FLAGS);
       mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
       //给SystemServer进程创建ProcessRecord，adj值，就是将SystemServer进程加入到AMS进程管理机制中，跟应用进程一致
       synchronized (this) {
           ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);
           app.persistent = true;
           app.pid = MY_PID;
           app.maxAdj = ProcessList.SYSTEM_ADJ;
           app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
           synchronized (mPidsSelfLocked) {
               mPidsSelfLocked.put(app.pid, app);
           }
           updateLruProcessLocked(app, false, null);
           updateOomAdjLocked();
 }