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

[Geoffrey Garen]

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
>>
>> _______________________________________________
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>> webkit-dev at lists.webkit.org
>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>>
>
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