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Posted to dev@lucy.apache.org by Marvin Humphrey <ma...@rectangular.com> on 2008/05/01 07:58:22 UTC
Re: Native callbacks
On Apr 26, 2008, at 12:55 PM, Marvin Humphrey wrote:
> This isn't a truly hard problem. There are definitely many ways to
> make this introspection data available using C. But all the ways
> I've thought of so far are ugly.
I've gotten this working. On its own, it's mildly ugly -- not too bad.
Things are improving step by step. At first, you couldn't override
anything. Then you could implement abstract methods using the host
language. Now you can override public methods.
There's one significant problem left that I'm aware of: Perl's SUPER
mechanism is broken with the vtable override.
Say you use the host language to override a method which was
implemented in C. The original binding invoked the implementing
function via the vtable. The override has now changed that vtable
pointer to be a callback. If you invoke SUPER from the subclass, it
invokes the callback, which invokes the native method again, and you
end up in an infinite loop.
sub serialize {
my ( $self, $outstream ) = @_;
$self->SUPER::serialize($outstream); # BOOM! Infinite recursion.
...
}
The solution, I believe, is to have the XS bindings not invoke via the
vtable, but instead invoke the implementing function directly.
Unfortunately, that means a lot more binding code, because each
override requires its own binding.
Now:
MODULE = KinoSearch PACKAGE = KinoSearch::Index::PostingList
chy_u32_t
get_doc_num(self)
kino_PostingList *self;
CODE:
RETVAL = Kino_PList_Get_Doc_Num(self);
OUTPUT: RETVAL
Fixed:
MODULE = KinoSearch PACKAGE = KinoSearch::Index::PostingList
chy_u32_t
get_doc_num(self)
kino_PostingList *self;
CODE:
RETVAL = kino_PList_get_doc_num(self);
OUTPUT: RETVAL
MODULE = KinoSearch PACKAGE = KinoSearch::Index::SegPostingList
chy_u32_t
get_doc_num(self)
kino_SegPostingList *self;
CODE:
RETVAL = kino_SegPList_get_doc_num(self);
OUTPUT: RETVAL
MODULE = KinoSearch PACKAGE = KinoSearch::Index::MultiPostingList
chy_u32_t
get_doc_num(self)
kino_MultiPostingList *self;
CODE:
RETVAL = kino_MultiPList_get_doc_num(self);
OUTPUT: RETVAL
Fortunately, most of the binding code gets auto-generated these days,
so once the auto-generation code gets patched the suffering will
primarily take the form of slower compiles rather than increased
maintenance costs.
Marvin Humphrey
Rectangular Research
http://www.rectangular.com/
Re: Native callbacks
Posted by Marvin Humphrey <ma...@rectangular.com>.
On Apr 30, 2008, at 10:58 PM, Marvin Humphrey wrote:
> There's one significant problem left that I'm aware of: Perl's SUPER
> mechanism is broken with the vtable override.
> The solution, I believe, is to have the XS bindings not invoke via
> the vtable, but instead invoke the implementing function directly.
> Unfortunately, that means a lot more binding code, because each
> override requires its own binding.
I finally got around to implementing this, and it turns out to have
been surprisingly easy. The commit diff was only 137 lines long.
http://www.rectangular.com/pipermail/kinosearch-commits/2008-June/001277.html
The size of the autogenerated binding file, KinoSearch.xs, went from
13442 to 18401 lines. On my Core 2 Duo MacBook Pro, compile time
increased from about 15 to 20 seconds for that file, and from about 55
to 60 seconds for all of KS. That's perfectly acceptable, and a
smaller increase than I'd expected.
The behavior of vtable methods is now virtually indistinguishable from
that of native Perl methods from the point of view of the library
user. The only difference is that because the vtable pointers for
subclasses are set when the DynamicVirtualTable object is created (the
first time it is needed by a new object), dynamically generated
methods created after that time won't trigger an override. That's an
esoteric use case, and I don't think it's even worth mentioning in the
documentation.
Marvin Humphrey
Rectangular Research
http://www.rectangular.com/