[Scilab-users] Counter of pointers to an XML object, and clear destructor

[Samuel Gougeon]

Hello,

I am doing some tests about the save() function, in order to document 
its behavior when saving pointers to some objects.

There is the case of XML objects:
Contrarily to graphic handles, that are pointers whose reloading 
restores the pointed graphics, saving XML pointers is possible, but then 
their reloading does NOT restore the XML document.
Then, when digging in Bugzilla in order to search for features about 
this and the clear() function applied to XML pointers, i've found back 
the following comment from Calixte 
<http://bugzilla.scilab.org/show_bug.cgi?id=13398#c2>, referring to an 
expected change of Scilab 6 with respect to Scilab 5:

/With Scilab 6, things will be easier since each data will have a 
reference counter [of pointers to it] which will allow to call a kind of 
destructor when the reference count will be zero.//
/
In practical, this new feature looks still not to be implemented. Here 
is an illustration:

// Let's create an XML document and a pointer "doc" to it:
--> doc = xmlReadStr("<root><a att=""foo"" 
rib=""bar""><b>Hello</b></a></root>")
  doc  =
XML Document
url: Undefined
root: XML Element

// Now, let's make a copy of the pointer:
-->doc2=doc
  doc2  =
XML Document
url: Undefined
root: XML Element

--> doc2==doc
  ans  =
   T T    <<< this double True is strange, but it's not the matter here

// Then let's clear both pointers: If a counter actually exists,
// it shall be set to 0 afterwards.
// And if the automatic destructor is implemented, then this should
// automatically delete the XML document. What's the reality?:
--> clear doc doc2   // OK
-->  xmlGetOpenDocs()
  ans  =
        ans(1)
XML Document
url: Undefined
root: XML Element

The document still exists. So, the automatic destructor is not yet 
implemented,
at least for XML objects.

Is it a pity? To me, the reverse approach would be more relevant:
Deleting an object should clear all its pointers. For instance, with the 
XML example
hereabove, deleting the document should clear doc and doc2.
It's unfortunately not the case:
--> xmlDelete(xmlGetOpenDocs()(:))  // cleaning the area
--> doc = xmlReadStr("<root><a att=""foo"" 
rib=""bar""><b>Hello</b></a></root>");
--> doc2 = doc;
--> xmlDelete(doc)
--> isdef(["doc" "doc2"],"l")
  ans  =
   T T
--> doc
  doc  =
-->

This is the same issue with graphic handles when the figure they point 
to has been closed:
We then get some still existing /but invalid/ handles, instead of 
properly clearing them.

Regards
Samuel


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