Zygot启动SystemServer：

pid = Zygote.forkSystemServer
//z0ygote 进程：pid = 子进程pid
//子进程：pid = 0

if(pid = 0){
    if(hasSecondZygote(abiList)){
        waitForSecondaryZygote(socketName);
    }
    zygoteServer.closeServerSocket();
    // SystemServer.main 方法。启动SystemServer
    return handleSystemServerProcess(parsedArgs);
}

return null;

handleSystemServerProcess(parsedArgs);
    -> ZygoteInit.zygoteInit
        //开启Binder线程池
        ->ZygoteInit.nativeZygoteInit();
            ->AndroidRuntime->onZygoteInit(); 
        //运行SystemServer.main 
        ->RuntimeInit.applicationInit();
            mMethod.invoke();//通过反射运行SystemServer.main

SystemServer进程：

//初始化SystemServer上下文

1. createSystemContext();
   ->ActivityThread.systemMain();
   ->ActivityThread.attach();
   ->ContextImpl context = ContextImpl.createAppContext(this,getSystemContext().mPackageInfo);
   mInitialApplication = context.mPackageInfo.makeApplication(true,null);//通过反射创建Application
   //创建SystemServiceManager

2. mSystemServiceManager = new SystemServiceManager(mSystemContext);

3. startBootstrapServices(t);//引导服务 -- AMS
   android(10) 开始有ATMS:
   1. 创建 ATMS(ActivityTaskManagerService) -- 管理Activity
   mService = new ActivityTaskManagerService();
   publishBunderService(Context.ACTIVITY_TASK_SERVICE,mService);//注册Binder服务
   mService.start();
   2. 创建AMS(ActivityManagerService ) --
   mService = new ActivityManagerService();
   1. BroadcastConstants
   2. ActivityServices
   3. BatteryStatsService
   4. ProcessStatsService
   5. mActivityTaskManager.initialize
   mService.start();

4. startCoreServices(t);//核心服务

5. startOtherServices(t);//其他服务 --WMS
   mActivityManagerService.systemReady()//启动Launcher
   ->ActivityStarter.execute(); 栈的管理相关
   -> startActivityHome();
   startSystemUI();//启动SystemUI

SystemServiceManager:管理服务的生命周期
ServiceManager：管理Binder服务的

resumeTopActivityInnerLocked
-> mStackSupervisor.startSpecificActivity
-> 进程存在 -- c
-> 进程不存在--
AMS创建Socket 通知 Zygote 创建进程
ZygoteServer.runSelectLoop(abiList);
-->通过反射启动ActivityThread.main
->thread.attach();
->mgr.attachApplication(mAppThread,startSeq);//把应用句柄发送给AMS.这个句柄是ApplicationThread通信。ApplicationThread是一个Binder对象
-> mStackSupervisor.startSpecificActivity
-> ActivityThread.handleLaunchActivity
-> performLaunchActivity();
-> mInstrumentation.newActivity(); //反射创建Activity
-> mInstrumentation.callActivityOnCreate();//调用onCreate方法