[webkit-dev] New marking model for GC collected objects

[Zoltan Herczeg]

Darin has already submitted a big patch to the bug report, which hopefully
solve all of these issues.

Zoltan

> In WTF_USE_JSVALUE32 DateInstance needs to override createStrucutre to
> remove the HasDefaultMark bit
>
> --Oliver
>
> On Sep 2, 2009, at 6:54 AM, Zoltan Herczeg wrote:
>
>> Hi Geoff,
>>
>> That function is not called.
>>
>> I have opened a bug report for this issue (a simple failed example
>> included)
>> https://bugs.webkit.org/show_bug.cgi?id=28909
>>
>> Zoltan
>>
>>> Hi Zoltan.
>>>
>>> JSWrapperObject::markChildren is responsible for marking the
>>> internalValue of a DateInstance. Is that function not being called?
>>>
>>> Geoff
>>>
>>> On Sep 1, 2009, at 6:16 AM, Zoltan Herczeg wrote:
>>>
>>>> Hi Oliver,
>>>>
>>>> it seems on ARM using WTF_USE_JSVALUE32, the internal value of a
>>>> date
>>>> object is sometimes freed by the garbage collector.
>>>>
>>>> More specifically:
>>>> The double (millisecond) representation of a date object (returned
>>>> by a
>>>> "new Date" expression) is stored in JSWrapperObject:
>>>> m_internalValue. This
>>>> m_internalValue points to a JSNumberCell, which stores the double
>>>> value.
>>>> Although this JSNumberCell is referenced by m_internalValue, the GC
>>>> still
>>>> collects its memory space.
>>>>
>>>> How can I fix this bug with the new mark() model?
>>>>
>>>> Zoltan
>>>>
>>>>> Last night I landed a patch that replaces the old recursive marking
>>>>> functions with a new iterative model that uses an explicit mark
>>>>> stack.  This means that any custom mark methods that you need to
>>>>> write
>>>>> now need to be slightly different from what they were previously,
>>>>> i'll
>>>>> attempt to summarise here.
>>>>>
>>>>> The most obvious change is that an object is no longer responsible
>>>>> for
>>>>> marking itself instead the recursive mark methods have been
>>>>> replaced
>>>>> by a new virtual markChildren(MarkStack&) which is responsible for
>>>>> appending an objects children to the stack.
>>>>>
>>>>> The MarkStack is a very simple class, and the only method you
>>>>> really
>>>>> need to know about is MarkStack::append which adds a new object to
>>>>> the
>>>>> stack.
>>>>>
>>>>> The changes to how your custom marking functions are implemented
>>>>> are
>>>>> trivial, but here's a simple example
>>>>> void MyAwesomeObject::mark()
>>>>> {
>>>>>    Base::mark();
>>>>>    if (!m_child.marked())
>>>>>        m_child.mark();
>>>>> }
>>>>>
>>>>> Becomes
>>>>> void MyAwesomeObject::markChildren(MarkStack& markStack)
>>>>> {
>>>>>    Base::markChildren(markStack);
>>>>>    markStack.append(m_child);
>>>>> }
>>>>>
>>>>> And that's it, you're done.
>>>>>
>>>>> It's important to note that you will never be in a position where
>>>>> you
>>>>> call markChildren yourself, if you are that is an error.
>>>>>
>>>>> --Oliver
>>>>>
>>>>> _______________________________________________
>>>>> webkit-dev mailing list
>>>>> webkit-dev at lists.webkit.org
>>>>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>>>>>
>>>>
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>>>> webkit-dev at lists.webkit.org
>>>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>>>
>>>
>>
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>
>