Hi Eliot,
Let me check...

2018-03-27 21:14 GMT+02:00 Eliot Miranda <eliot.miranda at gmail.com>:

> HI Nicolas,
>
> On Tue, Mar 27, 2018 at 3:33 AM, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
>
>> Hi Bob,
>> yes, you force me to rethink. The way mark and sweep GC works, cycles in
>> object graphs do not matter.
>> As long as the objects in the cycles are only pointed to weakly from
>> roots,
>>
>> | value weak array2 |
>> value := Array new.
>> weak := WeakArray with: value.
>> 3 timesRepeat: [Smalltalk garbageCollect].
>> self assert: (weak count: #notNil) = 1. "Not yet reclaimed, thisContext
>> points to it thru value variable"
>> value := nil.
>> 3 timesRepeat: [Smalltalk garbageCollect].
>> self assert: (weak count: #notNil) = 0. "This time, it is reclaimed"
>>
>> "Example of cycle"
>> value := Array new: 1.
>> array2 := Array with: value.
>> value at: 1 put: array2.
>> weak := WeakArray with: value.
>> array2 := nil.
>> value := nil.
>> 3 timesRepeat: [Smalltalk garbageCollect].
>> self assert: (weak count: #notNil) = 0. "The value is reclaimed despite
>> the cycle"
>>
>> It's then VW that behaves strangely: I did not find any pointer to the
>> class nor its metaclass apart themselves
>> (I took care to not add the metaclass to metaclass superclass subclasses,
>> because those are not weak).
>> This has obscured my mind.
>> Sorry for the noise.
>>
>
> Is there difference between 32-bit and 64-bit VisualWorks?  Like Spur,
> 64-bit VW uses a class table, whereas 32-bit VW has class pointers in
> object headers.  So if you see the behavior in one but not the other that
> could point to a bug in tracing the class table (and its likely my bug).
>
> 2018-03-26 23:15 GMT+02:00 Bob Arning <arning315 at comcast.net>:
>>
>>> Other that the WeakValueDictionary, is there anything referencing either
>>> the class or metaclass? If not, then they would be collected. Perhaps VW is
>>> saving a reference elsewhere?
>>>
>>> On 3/26/18 3:07 PM, Nicolas Cellier wrote:
>>>
>>> Hi all,
>>> while porting MatFileReader to Squeak, I encountered this questionable
>>> behaviour:
>>>
>>> I create classes on the fly for holding Matlab struct().
>>> I want those classes to be garbage collected when no more used.
>>>
>>> If I store the classes in a WeakArray, then this should normally not
>>> work:
>>> I mean that the classes should not be reclaimed.
>>> Why?
>>> Because the metaclass points strongly to the class (via thisClass
>>> variable).
>>> And the metaclass can't be reclaimed either, because it still has an
>>> instance.
>>> That's what happens in Visualworks, classes put in a WeakArray are never
>>> reclaimed.
>>> Fortunately, there is some Ephemeron support in VW to work around this
>>> (such loop are detected by ephemerons, and strong references by some object
>>> ephemerely pointed to does not count).
>>>
>>> In Squeak, I used a WeakValueDictionary, and to my surprise, discovered
>>> that the classes were reclaimed.
>>> Is this a bug?
>>>
>>> Nicolas
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
> --
> _,,,^..^,,,_
> best, Eliot
>
>
>
>
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