From: Garthy D <garthy_lmkltybr@...>
Date: 2013-01-27T16:21:31+09:00
Subject: Re: Soft object reference for mark and sweep


Hi Robert,

On 27/01/13 02:46, Robert Klemme wrote:
> On Sat, Jan 26, 2013 at 9:52 AM, Nokan Emiro<uzleepito@gmail.com>  wrote:
>>
>>>
>>> Any ideas as to a good way or suitable mechanisms to implement this?
>>
>>
>> Just a silly one:  if you seldom use that Hash in the store, you can
>> eliminate it.  You could
>> still lookup your objects by iterating trough ObjectSpace and find them.
>> But this way the
>> GC will be able to drop objects if there's no reference to them.  Basically
>> what you do here
>> the same old stuff:  a trade off between memory and CPU.  You have to decide
>> if lookup
>> speed is more important than memory footprint or the other way around.
>> (...or wait for a
>> less silly answer here... :)
>
> I think using WeakReference is even better because ObjectSpace lookup
> is slow and does not work in some circumstances (JRuby with specific
> settings).
>
> http://www.ruby-doc.org/stdlib-1.9.3/libdoc/weakref/rdoc/index.html
>
> If need by one can always create a special Hash wrapper which converts
> from and to WeakReference on insert and retrieval.

Thanks for that. I didn't even know WeakRef existed! That's going to 
open up a wide range of solutions now. Looking at the implementation, 
it's using finalizers, and I had been wondering if finalizers were going 
to lead to a potential solution.

The WeakRef interface worries me though. You'd normally expect to see 
just one call on such a thing (lock, which turns weak to strong/fail) 
and maybe a check call, with a big warning that the result might change 
post-check. A delegation-style interface with a check only seems a bit 
unusual. However, I may just not have a proper understanding of how it 
works yet.

Still- it's opened up a bunch of possibilities and ideas- lots of things 
to look into and explore. Thankyou again Robert for yet another one of 
your excellent suggestions. :)

Cheers,
Garth