Err, my bad...
In VW, reclaimed objects are not replaced by nil but by 0 (zero).

The example correctly answer 0 if I replace
     ^weak count: [:e | e ~= 0].

Cross dialect is a path full of pitfalls

2018-03-27 21:41 GMT+02:00 Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com>:

> Both vw7.8 32bits and vw8.3 64bits return 1 to this test:
>
>     | superStruct meta struct weak |
>     superStruct := Object.
>     meta := Metaclass new.
>     meta hash.
>     meta setSuperclass: superStruct class.
>     meta methodDictionary: MethodDictionary new.
>     meta setInstanceFormat: (Behavior formatFromType: #none super:
> superStruct class instVars: Array new).
>     struct := meta new.
>     struct hash.
>     struct setSuperclass: superStruct.
>     struct methodDictionary: MethodDictionary new.
>     struct setInstanceFormat: (Behavior formatFromType: #none super:
> superStruct instVars: Array new).
>     struct instanceVariables: Array new.
>     struct setName: 'TestStickyWeak'.
>     weak := WeakArray with: struct.
>     meta := struct := nil. "break references"
>     3 timesRepeat: [ObjectMemory garbageCollect].
>     weak count: #notNil.
>
>
>
> 2018-03-27 21:20 GMT+02:00 Nicolas Cellier <nicolas.cellier.aka.nice@
> gmail.com>:
>
>> 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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