一、概念

Android10（API29）开始，ActivityTaskManagerService 接管 ActivityManagerService。

二、启动ATMS过程

三、启动APP & 跳转Activity过程

3.1 Activity → ATMS

启动一个 APP 或跳转一个 Activity 都是调用的 startActivity()，进而调用 startActivityForResult()。

3.1.1 Activity 

Activity{
    public void startActivity(Intent intent, @Nullable Bundle options) {
        startActivityForResult(intent, -1, options);
    }
    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
        //委托给Instrumentation来启动
        Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options);
        mMainThread.sendActivityResult(mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData());
    }
}

3.1.2 Instrumentation

Instrumentation{
    public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, String target, Intent intent, int requestCode, Bundle options) {
        //获取一个Binder，它是ActivityTaskManagerService的proxy，然后调用startActivity()进行跨进程通信
        int result = ActivityTaskManager.getService().startActivity(whoThread,
            who.getOpPackageName(), who.getAttributionTag(), intent,
            intent.resolveTypeIfNeeded(who.getContentResolver()), token, target,
            requestCode, 0, null, options);
    }
}

ActivityTaskManager{
    public static IActivityTaskManager getService() {
        return IActivityTaskManagerSingleton.get();
    }
    //一种单例模式
    private static final Singleton<IActivityTaskManager> IActivityTaskManagerSingleton = new Singleton<IActivityTaskManager>() {
        @Override
        protected IActivityTaskManager create() {
            //获取ATMS的代理对象Binder
            final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
            return IActivityTaskManager.Stub.asInterface(b);
        }
    };
}

3.2 ATMS → PMS

ActivityTaskManagerService{
    public final int startActivity(IApplicationThread caller, String callingPackage, String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId());
    }
    private int startActivityAsUser(IApplicationThread caller, String callingPackage, @Nullable String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
        //获取ActivityStarter实例，去执行execute方法
        return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
            .setCaller(caller)
            ...
            .execute();
    }
}

ActivityStarter{
    int execute() {
        if (mRequest.activityInfo == null) {
            mRequest.resolveActivity(mSupervisor);
        }
    }
    static class Request {
        void resolveActivity(ActivityTaskSupervisor supervisor) {
            //AndroidManifest中intent标签
            resolveInfo = supervisor.resolveIntent(intent, resolvedType, userId, 0, computeResolveFilterUid(callingUid, realCallingUid, filterCallingUid));
            //转为Activity标签
            activityInfo = supervisor.resolveActivity(intent, resolveInfo, startFlags, profilerInfo);
        }
    }
}

ActivityTaskSupervisor{
    ResolveInfo resolveIntent(Intent intent, String resolvedType, int userId, int flags, int filterCallingUid) {
        //通过ATMS获取抽象类PackageManagerInternal
        //PMS内部类PackageManagerInternalImpl实现了它（内部类持有外部类，就可以调用PMS的方法了）
        //resolveIntent()会将从PMS的mPackages中查询到的ActivityInfo赋值给ResultInfo
        mService.getPackageManagerInternalLocked().resolveIntent(intent, resolvedType, modifiedFlags, privateResolveFlags, userId, true, filterCallingUid);
    }
    //将获取的ResultInfo转为ActivityInfo
    ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags, ProfilerInfo profilerInfo, int userId, int filterCallingUid) {
        final ResolveInfo rInfo = resolveIntent(intent, resolvedType, userId, 0, filterCallingUid);
        return resolveActivity(intent, rInfo, startFlags, profilerInfo);
    }
}

3.3 AMS → ApplicationThread