title: What is x86_thread_state64_t & thread_act_t?
body: <p>I was looking into source code of <a href="https://github.com/StarProject/StarRuntime" rel="nofollow">StarRuntime</a> and I came across two terms x86_thread_state64_t &amp; thread_act_t.</p>
  
  <p>I tried to Google it but there is not much documentation. 
  I see it being used consistently in apple open source projects?
  Can someone explain me what are they?</p>