Re: [xml] Query Regarding Buffer allocation scheme in Libxml

[Daniel Veillard <veillard redhat com>]

On Wed, Jul 02, 2008 at 07:15:00PM +0800, Ashwin wrote:
> Hi Daniel,

  Hi Ashwin

>           I have a query regarding the buffer allocation scheme used in
> libxml, each time a document is sent for parsing libxml creates a buffer of
> size 4k*2 initially, and then increases this if the doc happens to exceed
> this size. My query is, whether there is some specific reason why the
> original buffer is not used, rather than allocating another buffer and doing
> a memmove.  

  Good question, it's an optimization I tried to do ...

  I have looked at that a long time ago. Basically you would need to mark
the buffer immutable (that is easy) but also change the parser low level
to detect the end not on the 0 byte in the termination string but based on
the index in the string (since the API can take any kind of encoding,
the API uses a string lenght index, but internally the last character is
detected via the 0 character at the end). An intermediate approach could have
been to start parsing directly from an immutable buffer based on the input
string and just switch to a small normal buffer when getting to the end of
the input. But in any case those were significant code changes in really
critical parts of the parser and I had stability problems with the result
so I dropped the patch and never commited it. I guess the improvement
would interest only those using libxml2 in embedded system, and well 
your question seems to confirm this ;-)

Daniel

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