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Re: [Xen-API] Xen-API C Bindings, version 0.4.1

On Tue, Aug 08, 2006 at 10:06:52PM +0100, Ewan Mellor wrote:
> On Tue, Aug 08, 2006 at 04:06:47PM -0400, Daniel Veillard wrote:
> >   When using XPath with constant string, there is a serious optimization 
> > consisting of compiling first the XPath, and then reusing the compiled
> > XPath instead for the repetive queries. But it's probably a bit early for
> > optimization.
> I'm doing this already, no?

  heh, right, I misread :-)

> Or is there another optimisation that I don't
> know about?

  If you can reuse the xmlXPathContext that could be non neglectible too
but thread safety becomes a concern. Only one thread at a time can use it

> >    I agree with the other points raised by Dan. I will add another one,
> > the use of enum within public structures and parameters or return of 
> > functions, this is a very weak point of C, you don't have a good garantee
> > of allocation size, this may vary from one compiler to another, or
> > if you grow the number of items in the enum, I would avoid that and
> > use int (but document that it's supposed to be an enum), you loose a bit
> > of typechecking by compiler but gain ABI stability.
> That's an interesting point.  I thought that enums were defined to be the same
> size as int, but looking around it seems more complicated than this!

  I have seen ABI breakage because the number of values grew up and the
compiler decided to allocate more bytes, ouch ...


Daniel Veillard      | Red Hat http://redhat.com/
veillard@xxxxxxxxxx  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/

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