Zygote進程
Zygote進程啟動之后，調用startSystemServer會啟動SystemServer進程

SystemServer進程
在SystemServer類中有一個init2方法，它會創建一個ServerThread線程在它的run方法里面注冊了各種各樣的Service服務。

ServiceManager相關和如何啟動
1、首先先獲取IServiceManager(aidl文件)接口，此后所有的調用都是調IServiceManager接口的方法。
啟動服務 ServiceManager.addService(name,service)，調用的getIServiceManager().addService(name, service)。

2、ServiceManager本身是如何啟動的？
它在c層通過getContextObject進行轉換而來

sp<IServiceManager> defaultServiceManager()
{
    if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
    {
        AutoMutex _l(gDefaultServiceManagerLock);
        if (gDefaultServiceManager == NULL) {
            gDefaultServiceManager = interface_cast<IServiceManager>(
                ProcessState::self()->getContextObject(NULL));
        }
    }
    return gDefaultServiceManager;
}

SystemServer中啟動ActivityManagerService

在SystemServer中調用 context = ActivityManagerService.main(factoryTest)
在main方法里面創建AThread線程并在該線程里面new ActivityManagerService對象，等它創建完成之后賦給變量mSelf變量。

private void main(){
    ActivityManagerService m = thr.mService;
    mSelf = m;
    ActivityThread at = ActivityThread.systemMain();//創建ActivityThread
    mSystemThread = at;
    Context context = at.getSystemContext(); //獲取系統上下文對象
    context.setTheme(android.R.style.Theme_Holo);//設置主題
    m.mContext = context;
    m.mFactoryTest = factoryTest;
    m.mMainStack = new ActivityStack(m, context, true);

    m.mBatteryStatsService.publish(context);
    m.mUsageStatsService.publish(context);
    
}

在ActivityThread.systemMain()-->attach()里面創建
mInstrumentation = new Instrumentation();

ContextImpl context = new ContextImpl();
context.init(getSystemContext().mPackageInfo, null, this);
Application app = Instrumentation.newApplication(Application.class, context);
mAllApplications.add(app);
mInitialApplication = app;
app.onCreate(); 
            

調用ActivityManagerService.setSystemProcess方法

 public static void setSystemProcess() {
        try {
            ActivityManagerService m = mSelf;
            
            ServiceManager.addService("activity", m);
            ServiceManager.addService("meminfo", new MemBinder(m));
            ServiceManager.addService("gfxinfo", new GraphicsBinder(m));
            ServiceManager.addService("permission", new PermissionController(m));

            ApplicationInfo info =
                mSelf.mContext.getPackageManager().getApplicationInfo(
                        "android", STOCK_PM_FLAGS);
            mSystemThread.installSystemApplicationInfo(info);
       
            synchronized (mSelf) {
                ProcessRecord app = mSelf.newProcessRecordLocked(
                        mSystemThread.getApplicationThread(), info,
                        info.processName);
                app.persistent = true;
                app.pid = MY_PID;
                app.maxAdj = ProcessList.SYSTEM_ADJ;
                mSelf.mProcessNames.put(app.processName, app.info.uid, app);
                synchronized (mSelf.mPidsSelfLocked) {
                    mSelf.mPidsSelfLocked.put(app.pid, app);
                }
                mSelf.updateLruProcessLocked(app, true, true);
            }
        } catch (PackageManager.NameNotFoundException e) {
            throw new RuntimeException(
                    "Unable to find android system package", e);
        }
    }
    

SystemServiceManager

WindowManagerService
創建WindowManagerService它跟AMS一樣，都是通過new創建的。
通過下面代碼將AMS和WMS進行關聯。
ActivityManagerService.self().setWindowManager(wm);