解析SyetemServer进程启动过程

1.解析SystemServer进程

我们来看下SystemServer的mai函数

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

main函数只调用了run函数

private void run() {
       ...
           System.loadLibrary("android_servers");//1.加载so库
       ...
           //2.创建 SystemServiceManager， 创建并启动系统的各种服务 
           mSystemServiceManager = new SystemServiceManager(mSystemContext);
           LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
       ...    
        try {
           Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartServices");
           startBootstrapServices();//3.启动了AMS ,ATMS,PMS ...
           startCoreServices();//4.启动BatteryService，WebViewUpdateService,GpuService...
       //5.启动WMS,CameraService,BluetoothService,AudioService,LocationManagerService
           startOtherServices();
       } catch (Throwable ex) {
           Slog.e("System", "******************************************");
           Slog.e("System", "************ Failure starting system services", ex);
           throw ex;
       } finally {
           Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
       }
       ...
   }

看下startBootstrapServices函数

 private void startBootstrapServices(@NonNull TimingsTraceAndSlog t) {
   //1.创建并启动ATMS ,ServiceManager.addService("activity_task",atm)
     ActivityTaskManagerService atm = mSystemServiceManager.startService(
    ActivityTaskManagerService.Lifecycle.class).getService();
   // 2.创建并启动AMS 
   mActivityManagerService = ActivityManagerService.Lifecycle.startService(
               mSystemServiceManager, atm);
 // 注册binder,ServiceManager.addService("activity",mActivityManagerService)
   mActivityManagerService.setSystemProcess();
//3.创建并注册PMS,  注册binder, ServiceManager.addService("package", iPackageManager);
PackageManagerService.main()
}

看下startOtherServices函数

private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
   //创建WMS，并启动
    wm = WindowManagerService.main(context, inputManager, !mFirstBoot, mOnlyCore,
                    new PhoneWindowManager(), mActivityManagerService.mActivityTaskManager);
    //注册binder服务
   ServiceManager.addService(Context.WINDOW_SERVICE, wm, false,
                    DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PROTO);
  // AMS和WMS关联上
    mActivityManagerService.setWindowManager(wm);
}

2.ATMS和AMS的区别

AMS以前是管理四大组件，太庞大了,所以为了给AMS减压，把对Activity的管理抽到了ATMS.