[Python-Dev] Sharing expat instances

[Fredrik Lundh]

Martin v. Löwis wrote:

> >   - sort out expat bundling issues, and include cElementTree as well
> >     (using the same approach as above).

...

> > (one way to do this would be to add an "function pointer table" to pyexpat
> > that contains pointers to selected portions of the expat API, and then add
> > an indirection level to cElementTree)
>
> Ok, this sounds like a larger piece of work.

here's a plan:

1. add an Include/pyexpat.h header file which contains a structure
similar to the following:

#define PyExpat_DISPATCH_MAGIC  "... some magic string ..."

struct PyExpat_Dispatch {
    int size; /* size of this structure */
    int MAJOR_VERSION;
    int MINOR_VERSION;
    int MICRO_VERSION;
    ... (*ErrorString)(...)
    ... (*GetErrorColumnNumber)(...)
    ... (*GetErrorLineNumber)(...)
    ... (*Parse)(...)
    ... (*ParserCreate_MM)(...)
    ... (*ParserFree)(...)
    ... (*SetCharacterDataHandler)(...)
    ... (*SetCommentHandler)(...)
    ... (*SetDefaultHandlerExpand)(...)
    ... (*SetElementHandler)(...)
    ... (*SetNamespaceDeclHandler)(...)
    ... (*SetProcessingInstructionHandler)(...)
    ... (*SetUserData)(...)
    /* add new stuff to the end */
}

(this is the minimal stuff used by today's cElementTree; it can of course
be extended to cover a larger part of the current expat API)

2. during pyexpat initialization, initialize all members of this structure, and
make it available as a PyCObject:

    static PyExpat_Dispatch dispatch;

    dispatch.size = sizeof(dispatch):
    dispatch.MAJOR_VERSION = XML_MAJOR_VERSION;
    ...

    obj = PyCObject_FromVoidPtrAndDesc(
        &dispatch, PyExpat_DISPATCH_MAGIC, NULL
    );
    ... stuff object into module dictionary ...

3. in cElementTree (or _elementtree, or whatever the python version will
be named), import pyexpat, fetch the object, and verify

    - that the PyExpat_DISPATCH_MAGIC matches
    - that the size field is at least as large as sizeof(struct PyExpat_Dispatch)
    - that the version number matches (at least MAJOR and MINOR; I'm not
    sure under what circumstances they change the MICRO number)

4. in cElementTree (...), do all expat calls via the dispatch table.

comments ?

</F>