ActivityTaskManagerService 是 Android 系统中的核心服务之一，它负责管理应用程序的活动（Activity）和任务栈（Task Stack）。这里我们接上一篇内容继续分析 APP 启动流程， startActivity() 方法，调用了 ATMS，我们继续往下看。

一、ATMS源码分析

1、ActivityTaskManagerService

源码位置：/frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

startActivity

@Override
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());
}