好了，用上篇介绍的工具，跟踪了下startActivity在system_server中的流程，如下：

The picture below is the flow chart for how the source Activity start a target activity

Major includes four steps:
(1) Preparation, flow chart in blue;
(2) suspend the source activity, in yellow;
(3) Start the target application process once not yet created, also create the
Activity Thread, in Aubergine;
(4) Attach the target activity thread to application, in red, in this step,
application onCreate and activity onCreate are invoked.

System_server中的ActivityStack很重，里面维护了所有的activity的状态的栈，由于时间关系，没有深入研究。Application的onCreate主要是创建植根与此Application上的各个组件的Context。

有一点心得是如果要比较深入了解，必须自己去debug跟踪下，看别人的博客永远只是参考，而且容易打瞌睡。

Android start_activity流程