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

[Zoltan Herczeg]

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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>
>