[Vm-dev] [ENH] A better finalization support (VM & language side)

[Igor Stasenko]

On 9 March 2010 00:44, Levente Uzonyi <leves at elte.hu> wrote:
>
> On Mon, 8 Mar 2010, Igor Stasenko wrote:
>
>>
>> Please, review the
>> http://bugs.squeak.org/view.php?id=7473
>>
>> There are two sets of changesets - one for vmmaker and other is for
>> language-side.
>>
>> A VMMaker changeset is based on VMMaker-dtl.159.
>>
>> Here the little benchmark, between old and new weak registries:
>>
>> { WeakRegistry. WeakFinalizationRegistry } collect: [:class |
>>  | registry weaklings time1 time2 |
>>  registry := class new.
>>  WeakArray removeWeakDependent: registry.
>>
>>  weaklings := (1 to: 100000) collect: [:i | Object new ].
>>  time1 := [ weaklings do: [:each | registry add: each ] ] timeToRun.
>>  weaklings at: 100 put: nil.
>>  Smalltalk garbageCollect; garbageCollect.
>>  time2 := [ registry finalizeValues ] timeToRun.
>>  time1 @ time2
>> ]
>> {7816 at 41 . 4114 at 0}
>>
>> While its not much better at first benchmark (since using the same
>> approach to store objects in one dictionary),
>
> I took a quick look and found that you omitted the semaphore from
> WeakFinalizationRegistry. I think it won't work this way.
>

The point is, that new implementation don't touching the
'valueDictionary' during finalization,
and therefore from this side, there is no concurrency issues.

Adding/accessing items in the list is not protected. But i think the
main reason why we having a semaphore here is to protect from
interrupts caused by garbage collector and finalization process.
If you think we should also protect it from concurrent access , when
populating it - i could add the semaphores.

>> while other is significant, since there is no longer need to scan a
>> whole collection to detect an items which become a garbage.
>
> That's great.
>
>>
>> Btw, i wonder, why current WeakRegistry using a WeakKeyDictionary
>> instead of WeakIdentityKeyDictionary?
>> Isn't a weak refs is identity-based?
>>
>
> I found it strange too, but I think the users of WeakRegistry don't
> implement their own #hash and #=, though I didn't check that. Using a
> WeakIdentityKeyDictionary could also mean better performance in most cases.
>
>> I am also a bit wonder, why WeakRegistry has to support a copy protocol?
>> It may lead to unpredictable behavior once you try to copy such kind
>> of container, no matter how well you protect it.
>
> I think copy is supported because WeakRegistry is a collection. I wonder how
> could you get the unpredictable behavior with the current implementation.
>

well, potentially, it could lead to making finalization twice (by each
registry object), since when you copying registry you doubling the
number of references to all executor objects which is held strongly by
registry.

>
> Levente
>
>>
>> --
>> Best regards,
>> Igor Stasenko AKA sig.
>>
>



-- 
Best regards,
Igor Stasenko AKA sig.