Re: Why does the garbage collector use a giant ring instead of lists?

Off hand, I don't recall exactly - it may simplify the implementation. 
You might check out Henry Baker's paper "The treadmill: real-time garbage collection without motion sickness" and see if there was a good reason.

On 2011-07-13 Wed, at 07:22 PM, dennisf486 wrote:
> So I'm digging into the garbage collector trying to debug this strange problem with my Io block() object created in a do() getting freed even though my C++ code is consistently marking it.  There's a surprisingly small amount of code that implements Io's garbage collector.  There's one thing I don't understand though - what I at first took to be linked lists for the list of white, gray, black, and freed objects is not really linked lists, it's rings.  In fact, instead of four separate lists (or rings) all four colors are in one giant ring, and the list "heads" are just pointers into the ring.
> 
> My first clue was I expected COLLECTMARKER_FOREACH would be implemented like:
> while (v->next != NULL) ...
> 
> but instead I found this:
> while (v->color == c) ...
> 
> So, you could think of the structure as being like a big bracelet, and you count beads until you reach a band of a different color.  Although it conjures an interesting mental picture, it seems like a bizarre engineering choice.  What advantage is gained by doing this, versus just keeping them in four completely separate linked lists and using NULL to mark the end of the list?
>