Re: [rvm-research] Regarding GC

The single statement in your snippet  is eventually expanded by the 
compiler into a sequence of indirect loads (think assembly level 
programming).     A GCmap is (logically) created for each such 
(assembly-like) instruction that contains the current live stack roots. 
So, before the snippet it will contain what head (a local variable) points 
to and then as the sequence is executed (one indirection at a time) and 
head is updated, the stack root set is updated.

So the answer is 
  - yes, there are points in the sequence where a stack root is pointing 
to each node in the list 1-6, but 
  - no, there is not a single point in the sequence where the stack roots 
point to all these nodes

Mike
_____________________________________________________________
Michael Hind, Senior Manager, Programming Technologies Department 
IBM T.J. Watson Research Center
http://www.research.ibm.com/people/h/hind
914 945-2712
My internal blog:  https://w3-connections.ibm.com/blogs/hindsight



From:   Hari Krishnan <[email protected]>
To:     "General discussion of Jikes RVM design, implementation, issues, 
and plans" <[email protected]>
Date:   08/27/2014 12:21 PM
Subject:        [rvm-research] Regarding GC



Hi, 

I have a question. I just want to make if a scenario is possible to 
happen. The scenario goes like this.

I have a cycle of linked list. All nodes have id from 1 to 50 and they are 
arranged in order. There is a head pointer to a node with id 1. I am 
moving this head pointer to node with id 6. Does all the intermediate 
nodes have stack root pointing to them at the interim time during 
traversal? 
 for example 

fun(head){
head = head->next->next->next->next->next;
.........


}
In this above snippet,  do all of the intermediate nodes 2 through 5 has 
stack root ("head") pointing to them briefly? or VM figure out and 
calculate the address and move the root from node 1 to node 6 directly? 

Cheers
Hari.
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