preform GC modifications

[Thomas Schatzl]

Hi,

On 16.04.20 10:49, Ofir Gordon wrote:
> Thank you very much for the detailed answer.
> I'll take your recomendation to try and use a newer version, it just 
> that I'm working on a specific simulator which might have difficulties 
> with newer jdk versions, but it worth a try.
> 
> If it is ok I would like another followup question, regarding the actual 
> method in which the marking phase is preformed (again for the serial gc) 
> - when I follow after the calls from GenCollectedHeap::collect(), I can 
> see that finaly it gets in a method 
> GenCollectedHeap::gen_process_strong_roots(), where I believe the actual 
> marking happens? then inside the method it goes to 
> SharedHeap::process_strong_roots, and in there, there are many oops_do() 
> calls of different classes.
> So my question is, where exactly the marking loop happens for this case? 
> and how can it be specified for different types of gc (cause not all go 
> the same code paths...)

Probably you are looking at Serial GC minor collections which are called 
in that path, but you are interested in major collections which applies 
the Mark-Sweep-Compact algorithm that is executed only once in a while 
(i.e. when old gen is full).

The entry point you are looking for where marking is happening would be 
GenMarkSweep::mark_sweep_phase1().

The actual marking "loop" in Serial GC major gc is done using a 
recursion using an explicit (mark) stack (MarkSweep::_marking_stack and 
_objarray_stack) by calling MarkSweep::follow_stack() in 
MarkSweep::follow_root() which is called by these oops_do() methods you 
already found.

Minor gc uses Cheney's two-finger technique.

Thanks,
   Thomas