[Tclxml-devel] Tcl-DOM generic framework

[Joe E. <jen...@fl...>]

Steve et. al --

It looks like integrating dom::c into the new Tcl-DOM
generic framework is going to be more difficult than
I first expected.  Also, there are some serious pitfalls
in the generic implementation.

The main issue is that the generic layer checks the
Tcl_Obj 'typePtr' field of DOM node objects to determine
which DOM implementation created the node.  dom::c doesn't 
actually use a separate Tcl_ObjType to represent nodes; 
instead, it uses strings with handle semantics.

(Using strings with handle semantics is actually the safest
thing to do in the presence of [dom::DOMImplementation destroy].
Using a custom Tcl_ObjType can lead to Tcl_Obj's with dangling
pointers in their internal reps if you're not _extremely_ careful.)

Even if dom::c did use a custom Tcl_ObjType, there would still
be a danger if multiple DOMImplementations are loaded into the
same process.  It's very easy for the internal rep to be discarded,
and there's no way to get from the string rep back to the
DOMImplementation which created the node.

If there's only one DOMImplementation registered, this
problem won't be fatal (since the generic layer will just
dispatch to the single, default, DOMImplementation), but if
there are more than one the generic layer is likely to break
badly.

I'm not sure how to fix this.


--Joe English

  jen...@fl...