冷启动创建应用时，ActivityThread的主要方法：

1. main()
   -- 1. 开启消息循环
   -- 2. 通知ActivityManagerService
   -- 3. 添加GCWatcher
2. handleBindApplication()
   -- 1. 创建LoadedApk
   -- 2. 创建Instrumentation
   -- 3. 创建Application
   -- 4. 通过Instrumentation调用Application的onCreate()方法

main()

main方法是一个应用创建的入口，他主要做了3件事

1. 开启消息循环

调用Looper.prepareLoop() Looper.loop()，开启主线程的消息循环，以便于ApplicationThread调用ActivityThread中的生命周期方法。

public static void main(String[] args) {    ...    Looper.prepareMainLooper();    ActivityThread thread = new ActivityThread();    thread.attach(false);    if (sMainThreadHandler == null) {        sMainThreadHandler = thread.getHandler();    }    ...    Looper.loop();}

2. 通知ActivityManagerService

调用ActivityThread.attach()方法，attach()方法在调用了attachApplication()将ApplicationThread这个Binder交给了ActivityManagerService，意味着ActivityManagerService可以通过ApplicationThread控制我们的应用，建立了服务器端对客户端的通信渠道。

private void attach(boolean system){    ...    final IActivityManager mgr = ActivityManager.getService();    try {        mgr.attachApplication(mAppThread);    } catch (RemoteException ex) {        throw ex.rethrowFromSystemServer();    }    ...}

SDK26以后，去除了Native和Proxy，而是直接从ActivityManager(ServiceManager)中获取ActivityManagerService的Binder对象进行通信

3. 添加GCWatcher

在attach()方法中，添加了监听dialvik内存使用情况得监听者GcWatcher，当内存使用超过总容量的3/4，则打印Log进行记录，并且调用ActivityManagerService的releaseSomeActivities()进行内存释放操作，以防止内存溢出导致应用崩溃。

private void attach(boolean system){    ...    BinderInternal.addGcWatcher(new Runnable() {        @Override public void run() {            if (!mSomeActivitiesChanged) {                return;            }            Runtime runtime = Runtime.getRuntime();            long dalvikMax = runtime.maxMemory();            long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();            if (dalvikUsed > ((3*dalvikMax)/4)) {                if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)                        + " total=" + (runtime.totalMemory()/1024)                        + " used=" + (dalvikUsed/1024));                mSomeActivitiesChanged = false;                try {                    mgr.releaseSomeActivities(mAppThread);                } catch (RemoteException e) {                    throw e.rethrowFromSystemServer();                }            }        }    });    ...}

---

handleBindApplication()

ActivityManagerService=AMS

handleBindApplication的被调用时机是:

1. 通过上面AMS.attachApplication()后，AMS获得了控制应用的Binder对象ApplicationThread。
2. AMS进行了一系列操作后（这里先省略），调用了ApplicationThread的bindApplication()
3. bindApplication中通过消息机制，sendMessage到ActivityThread，调用了ActivityThread的handleBindApplication()

handleBindApplication是创建用于所需组件的入口，他主要做了4件事：

1. 创建LoadedApk

LoadedApk对象包含应用的所有信息

private void handleBindApplication(AppBindData data){    ...    final LoadedApk pi = getPackageInfo(instrApp, data.compatInfo,                    appContext.getClassLoader(), false, true, false);    ...}

2. 创建Instrumentation

Instrumentation是应用组件的管家，组件的生命周期方法都需要通过它来调用，是客户端与服务器端通信的最后一步。

private void handleBindApplication(AppBindData data){    ...    final ContextImpl instrContext = ContextImpl.createAppContext(this, pi);    try {        final ClassLoader cl = instrContext.getClassLoader();        mInstrumentation = (Instrumentation)            cl.loadClass(data.instrumentationName.getClassName()).newInstance();    } catch (Exception e) {        throw new RuntimeException(            "Unable to instantiate instrumentation "            + data.instrumentationName + ": " + e.toString(), e);    }    ...}

3. 创建Application

调用了LoadedApk.makeApplication()进行Application的创建

private void handleBindApplication(AppBindData data){    ...    app = data.info.makeApplication(data.restrictedBackupMode, null);    ...}

• 先通过ContextImpl.createAppContext(）获得Application的Context
• 再通过Instrumentation.newApplication()，用ClassLoder创建Applicaition
• 创建后Applicaition调用自身的attach(Context)方法，将Context与Applicaition绑定，完成创建

LoadedApk.classpublic Application makeApplication(boolean forceDefaultAppClass,            Instrumentation instrumentation) {    ...    Application app = null;    ...    ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);    app = mActivityThread.mInstrumentation.newApplication(            cl, appClass, appContext);    ...    return app;}

4. 通过Instrumentation调用Application的onCreate()方法

private void handleBindApplication(AppBindData data){    ...    mInstrumentation.callApplicationOnCreate(app);    ...}