Re: Traversing the stack frame and identifying "references"

>> But how can it be done when the garbage collector is written for  
>> languages like C++. Do we need to somehow ask the compiler to do  
>> that? Or some other techniques are used?

And I realized I did not really answer your question.
If you stick with the stock threading systems, you
may need to reverse-engineer it.  POSIX, at least at
one time, had some facility to enumerate threads, but
no guarantee that the threads that you got were all
of them, or were still active when you received word
of their existence.  (It's been something like twenty
years, perhaps they have fixed this.)

Plan B, probably never implemented for C++, is to write
your own threading system and write a compiler (or object
code mutator) that enforces cooperation with threads.
With your own threading system, you can pretty do what
you want, and in particular, you can notice which threads
have moved since the last GC -- there's room to fiddle
the design.

David Chase