On Thu, Oct 23, 2003 at 09:49:34AM -0700, James Berry wrote:
> Congratulations on the birth of your daughter.
Thanks :)
> The semantics of "here's the alignment that should be applied to a
> newly allocated block" versus "here's some details of how you'll be
> able to use custom memory management" seem very different to me.
I agree, but the fact remains that the following Q/A session will result in
a mess:
Q: what's the alignment I should use?
A: something smaller than the size of a pointer - like zero!
Result: part of - or everything of - the pointer can (and will) be overwritten
with user data. Thinking of it a bit more, I think a patch should be done to
XMLPlatformUtils::alignPointerForNewBlockAllocation that checks whether
XML_PLATFORM_NEW_BLOCK_ALIGNMENT < the pointer size, and if so makes it return
zero. The caller should check whether 0 was returned and not assume anything
about the pointer stored in the data area if it is. Like that, the semantics
become well-defined and the question gets a correct answer.
I'd agree that this problem is not necessarilly fixed the right way in the
patch I sent, but I think we agree there's a problem here.
> The fact that XMemory is the one and only user of the alignment function
> currently doesn't mean that we should assume it always will be.
I agree, but for that case the semantics "how to handle the alignment" should
be defined more clearly - e.g. as proposed above.
> So _if_ we're to alter XMemory behavior, which we haven't proven is needed
> yet, I would definitely want a different way to specify that.
As for the need to change: I think badly configuring at compile-time - such as
by following indications on this list: the two options given to me (0 and 1
alignment) would break Xerces badly in the current situation - should not
result in random (and certainly not in sure) crashes.
> I'll grant your statement that XML_PLATFORM_NEW_BLOCK_ALIGNMENT isn't
> document except in the header, and simply point out that there's much to
> Xerces platform porting that's documented nowhere but in the code.
That shouldn't be too much of a problem, as Doxygen is used to create the
documentation :)
Anyways, most projects (free and otherwise) have a lack of documentation. It's
not a reflection of the quality of the code or of the product, but it does make
life for the user a bit less easy..
> (1) Understand the problem
> (2) Architect a solution
> We haven't done (1) yet, and we're arguing about a (2) that has no
> purpose I can think of besides making things more complex.
I think we have done (1): I think we can both agree that
XMLPlatformUtils::alignPointerForNewBlockAllocation (which IMHO is badly named
because it doesn't actually align anything) shouldn't return false information
and, if it returns 0 (which it should on more occasions) that should actually
mean something useful.
IMHO, (2) is the next step and I am quite willing to propose patches to fix
the problem as soon as we agree on the problem..
rlc
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