Re: [rvm-research] Return barriers

Hi Dr. Erez,

Thank you. Appreciate the response.

Cheers
Hari.


On Mon, Feb 17, 2014 at 1:45 AM, Erez Petrank <[email protected]>wrote:

> Hari,
>
> The use of a return barrier to allow concurrent stack scanning has
> appeared in our VEE'09 paper. It may be useful to look at it.
>
> *Gabriel Kliot, Erez Petrank, and Bjarne Steensgaard. A Lock-Free,
> Concurrent, and Incremental Stack Scanning for Garbage Collectors
> <http://www.cs.technion.ac.il/~erez/Papers/sctack-scan-vee09.pdf>.  Proceedings
> of the 2009 ACM SIGPLAN/SIGOPS International Conference on Virtual
> Execution Environments (VEE'09) <http://www.cs.purdue.edu/VEE09/Home.html>,
> March 2009. *
>
> --Erez
>
> On Feb 14, 2014, at 5:48 AM, Hari Krishnan <[email protected]> wrote:
>
> 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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