Re: [rvm-research] Return barriers

Hi all,
I am implementing a Reference Counting based garbage collector. This
reference count implementation is concurrent as well as parallel capable of
collecting cycles efficiently. Every-time an object is pointed by any stack
root, I have to increment a separate counter in the object. This reference
count implementation is  mainly based on stack roots. So every object  has
a separate counter that counts the path from stack roots. So when any
object get the stack root, I have to increment it and so when ever any
object loses the support of stack roots I have to reduce that count. The
whole algorithm uses the stack roots as the fundamental idea. I could use
scanning of the stack in the collector part to identify the roots and
increment it. But that complicates our algorithm and have to change
algorithm to use deferred version of the algorithm which may or may not
impact the correctness of the algorithm (Although I started working out the
deferred version after realizing the features I wanted in Jikes RVM are too
hard to implement by myself and consumes lot of time). So I needed return
barrier to decrement the count of the object pointed by stack frame that is
about to be popped and identify when an objects gains the stack root. I
hope this clarifies my necessities.


On Thu, Feb 13, 2014 at 8:45 PM, Eliot Moss <[email protected]> wrote:

> On 2/13/2014 2:57 PM, Hari Krishnan wrote:
>
> > 1. I want to know how to activate the return barriers and let the
> mutators know that a activation
> > record is about to be popped from the stack.
>
> Return barriers are a comparatively new addition, so I am afraid I
> personally
> can't help you about them -- but I'm sure someone else can!
>
> > 2. How can I find if an object is pointed by stack root at the time of
> assignment?
>
> You can't.  Such assignments can get optimized in various ways that place
> the
> item into registers, etc.  You have to get by with occasional scanning of
> frames or similar measures.
>
> Perhaps if you told us more about the particular kind of collector and your
> goals we could be of more assistance.  There's a lot of knowledge here, but
> to tap into it you often have tell us the bigger picture.
>
> Regards -- Eliot Moss
>
>
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