lxml - The Python XML Toolkit

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December 2004

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2 discussions

[lxml-dev] Memory management redux
by Martijn Faassen Dec. 11, 2004

Dec. 11, 2004

Hi there, Inspired by discussions with Vic and through browsing the vlibxml2 code, I've implemented bit of memory management functionality which, after a lot of manual debugging, seems to be doing the right thing. So far... A new addition to the lxml trunk is nodereg, and associated testing stuff (noderegtest.pyx and test_nodereg.py). nodereg is a system for registering Python-level node proxies, plus some base classes for the document and node objects in a typical libxml2 tree wrapper. The nodereg module functionality can be used to make sure that memory (in particular libxml2 tree nodes) gets collected when it is possible, and not before. :) This sounds easy, but it is surprisingly tricky. Next: * look into hooking in libxml2's memory debugging functionality for testing. Investigate Vic's code in that area/get Vic's advice. * start rewriting etree, dom, or vlibxml2 to use nodereg. This will likely further evolve nodereg. * Add more functionality to nodereg. One thing that currently is not handled is attribute nodes, for instance. * Optimize nodereg. The strategy currently employed requires, in the worst case, a lot of full-tree walks to determine whether a node in the tree can be successfully garbage collected. We need to come up with some smart algorithm/datastructure to avoid this having to happen to often. Another thing I would really like to do is investigate adding weakref support to Pyrex. Right now I had to first jump through a bit of a hoop to make it work. Then later on I took a long time debugging an obscure case where there would be a remaining refcount on an object even if the only object still pointing to the object was a WeakValueDictionary. I finally traced it down to Pyrex introducing this. I'm not clear why, but somehow the base class got involved (which was not weakreferenceable as defined by Pyrex). This somehow managed to trick the object into keeping a reference while it shouldn't, causing it never to be deallocated. Being able to just say 'this class can be weakreferenced' in Pyrex should make this go away. Regards, Martijn

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[lxml-dev] reorganisation confusion
by Martijn Faassen Dec. 7, 2004

Dec. 7, 2004

Hi there, Tonight I attempted a package reorganisation myself, integrating vlibxml2 into lxml from the other direction, leaving most of lxml's build scripts and testing framework intact. My attempts are here: http://codespeak.net/svn/lxml/branch/lxml-reorg/ The build story works ('make' does the trick). The tests are picked up by the test runner. I noticed that on reorg-20041120 'make' tries to install in site-packages directly, which is something that doesn't happen on my branch. I think it's cleaner not to have to install in site packages just for testing, and the test.py runner takes care of this in lxml. Another thing I tried to do conscientiously on my branch is use 'svn move', so that version control history of various files is not lost during reorganisation. Did you use that, Victor? Everything is currently in the lxml directory (except for vlibxml2_mod.so, but I tried placing it there as well and it's an easy change to setup.py). The problem is that I can't get vlibxml2 tests to get anywhere near passing. When running the tests, I get many, many obscure errors along these lines: Exception exceptions.NameError: 'vlibxml2' in <lxml.vlibxml2_subclasses.xmlNodeSub object at 0x404337cc> ignored Alternate source organisations result in import errors instead.. I tried rearranging the source every which way, but I think the problem remains that vlibxml2_mod uses (through wrapfuncs.pxi) vlibxml2_subclasses.py, where vlibxml2_subclasses.py imports from vlibxml2_mod to actually do the subclassing. This circular setup is driving me rather crazy. I suspect that the original vlibxml2 setup had some magic source code organisation that somehow avoided this problem. I do not know where the magic is though; Victor, could you perhaps explain? Preferably I'd like to break this circular import, as it's obviously hard to maintain. I apparently can't do it. :) Is there any way to accomplish this? I understand that we need to subclass for weak-referencability, but is there any way to do this in .pyx code directly instead of in Python? Or could we make the weakreffable classes the root base class, so there's no need for them to inherit from vlibxml2_mod classes first, and then be used in vlibxml2_mod again? Please help! :) Regards, Martijn

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