Zygote进程
Zygote进程启动之后，调用startSystemServer会启动SystemServer进程

SystemServer进程
在SystemServer类中有一个init2方法，它会创建一个ServerThread线程在它的run方法里面注册了各种各样的Service服务。

ServiceManager相关和如何启动
1、首先先获取IServiceManager(aidl文件)接口，此后所有的调用都是调IServiceManager接口的方法。
启动服务 ServiceManager.addService(name,service)，调用的getIServiceManager().addService(name, service)。

2、ServiceManager本身是如何启动的？
它在c层通过getContextObject进行转换而来

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中启动ActivityManagerService

在SystemServer中调用 context = ActivityManagerService.main(factoryTest)
在main方法里面创建AThread线程并在该线程里面new ActivityManagerService对象，等它创建完成之后赋给变量mSelf变量。

private void main(){
    ActivityManagerService m = thr.mService;
    mSelf = m;
    ActivityThread at = ActivityThread.systemMain();//创建ActivityThread
    mSystemThread = at;
    Context context = at.getSystemContext(); //获取系统上下文对象
    context.setTheme(android.R.style.Theme_Holo);//设置主题
    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()里面创建
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(); 
            

调用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
创建WindowManagerService它跟AMS一样，都是通过new创建的。
通过下面代码将AMS和WMS进行关联。
ActivityManagerService.self().setWindowManager(wm);