[pypy-dev] Automated binding generation (and maintenance)

Shaheed Haque srhaque at theiet.org
Wed Oct 11 07:03:56 EDT 2017

Oh wait, I think I see that cling-config is installed by the cppyy
package. (Seems a tad confusing, ho-hum).

On 11 October 2017 at 10:29, Shaheed Haque <srhaque at theiet.org> wrote:
> Hi Wim,
> After reviewing your comments, I propose to check out rootcling. I
> initially had some trouble using pip3 to install the newer code, but
> that seems to have been resolved as of yesterday's 0.2.3 build. I did
> notice one message during the install which seems to be benign, so I
> mention it here merely in passing:
>   Running command /usr/bin/python3 -u -c "import setuptools,
> tokenize;__file__='/tmp/pip-build-spz01kkp/cppyy-backend/setup.py';f=getattr(tokenize,
> 'open', open)(__file__);code=f.read().replace('\r\n',
> '\n');f.close();exec(compile(code, __file__, 'exec'))" bdist_wheel -d
> /tmp/tmpe2h6yls0pip-wheel- --python-tag cp36
>   running bdist_wheel
>   running build
>   running build_ext
>   error: [Errno 2] No such file or directory: 'cling-config': 'cling-config'
> error
>   Failed building wheel for cppyy-backend
>   Running setup.py clean for cppyy-backend
> I'll no doubt be back with questions :-).
> Thanks for all the good work, Shaheed
> On 23 September 2017 at 06:24, Shaheed Haque <srhaque at theiet.org> wrote:
>> Wim,
>> Thanks for the detailed and thoughtful reply. I will digest and
>> respond when I am properly back in circulation.
>> On 15 September 2017 at 07:43,  <wlavrijsen at lbl.gov> wrote:
>>> Shaheed,
>>>> Ah, I had not realised rootcling existed. I've seen that I can invoke
>>>> it using Python version-specific paths...is this the correct way to
>>>> invoke it:
>>>> ROOTCLING=/usr/local/lib/python3.6/dist-packages/cppyy_backend
>>>> LD_LIBRARY_PATH=$ROOTCLING/lib $ROOTCLING/bin/rootcling -h
>>> Yes, and here's a description of the LinkDef.h format:
>>> https://root.cern.ch/root/html/guides/users-guide/AddingaClass.html#the-linkdef.h-file
>>>> or is there a recommended wrapper?
>>> No, but I'm going to add one for pip, same as I did for genreflex. I've
>>> been fleshing out the backend generation, taken over from Anto:
>>>   https://bitbucket.org/wlav/cppyy-backend
>>> where all that can live. I'm told that I'll need rootcling anyway for
>>> use of modules (see below).
>>>> I actually get some warnings and then the error:
>>> Add this set of exclusions to the selection.xml:
>>> <exclusion>
>>>    <class pattern="*thread_mutex*" />
>>>    <class pattern="*new_allocator*" />
>>>    <class pattern="*Alloc_hider*" />
>>> </exclusion>
>>> Of course, the larger problem of pulling in these standard libs over and
>>> over again is that it is a waste of cpu and memory, so I do want to see
>>> the file_name attribute fixed. As it stands, I'd simply exclude:
>>>    <class pattern="std::*" />
>>>    <class pattern="__gnu_cxx::*" />
>>> especially since they are already available by default. Note that those two
>>> rules cover the ones needed for new_allocator and Alloc_hider.
>>> However, there is a more efficient approach that is right around the corner
>>> (and has been right about the corner for a long time, so don't hold me to
>>> that). Next release now seems likely though.
>>> The long term goal has always been to use modules:
>>>   http://clang.llvm.org/docs/Modules.html
>>> but the original drivers (Apple, Google, and the C++ standards committee)
>>> have been going back and forth on it. Now, things are finally falling into
>>> place. Here's Google:
>>>   https://www.youtube.com/watch?v=dHFNpBfemDI
>>> And here's ROOT:
>>> https://indico.cern.ch/event/643728/contributions/2612822/attachments/1494074/2323893/ROOTs_C_modules_status_report.pdf
>>> The big deal is that C++ developers have an incentive to deploy modules, so
>>> being able to patch into that should be a huge time saver (and where they
>>> don't, rootcling will soon be able to create modules from headers). Note
>>> that modules don't come for free: it will require some ambiguity resolution,
>>> but that is typically a Good Thing (code-quality wise).
>>> Modules allow deserialization of only the piece of the AST that is actually
>>> being requested, saving memory. This as opposed to header files (whether or
>>> not precompiled) which pull in everything before them. See the status report
>>> above for the improvements in memory usage.
>>> And with modules, of course, selection becomes unnecessary (markup for
>>> automatic streamers may still be useful, but that is not relevant for
>>> bindings generation).
>>>> I did wonder if I was missing some "-isystem" includes, and tried
>>>> adding them but the --debug output from genreflex seemed to suggest
>>>> they were being ignored.
>>> Some flags are ignored as no-one was using them (so far). Some others
>>> are definitely obsolete by now.
>>>> What is interesting, and might possibly throw light on the selection
>>>> filter issue, is that the file name for the classes in
>>>> kjsinterpreter.h itself is always the empty string ''. Classes that
>>>> come from included files return non-empty strings such as
>>>> 'kjsobject.h' for 'KJSObject'.
>>> That's after the fact (i.e. what is stored); I don't see the rule being
>>> respected/used at all.
>>>> BTW, the reason for doing this is that lots of KDE code has multiple
>>>> classes and even namespaces in a single header file. Now, for
>>>> discoverability of the loaded objects, I find the incremental "pop
>>>> into cppyy,gbl on demand" somewhat limiting and I wanted to play about
>>>> with that. I could also workaround the filter issue if I precomputed
>>>> the needed names in a precursor pass.
>>> The issue here is the memory cost of loading things that won't get used
>>> in the end. This is why a functional dir() (which needs nothing but
>>> strings, after all), in conjunction with lazy loading/creation when a
>>> real access happens work well. LLVM is fully lookup based, btw. There
>>> is a custom layer on top of Cling to make enumeration possible.
>>>> Finally, and most importantly given the fidelity with which cppyy
>>>> renders the C++ code, I'm think about how Pythonisation customisation
>>>> might be handled: e.g. a Python wrapper layer to allow a
>>>> pointer-plus-size to render as a Python list/tuple, or generate a dict
>>>> mapping fora QSet, and so on. (I'm dimly aware of the
>>>> boost-recognition logic you have alluded to, this is specifically more
>>>> about Qt-specific patterns and ad-hoc scenarios).
>>> In 2015, a GSoC student fleshed this out. I never put it into PyPy b/c of
>>> a lack of test coverage, but did put in in PyROOT. Here's an example of
>>> the "pointer-plus-size" pythonization (from ROOT.py):
>>>     # python side pythonizations (should live in their own file, if we get
>>> many)
>>>       def set_size(self, buf):
>>>          buf.SetSize(self.GetN())
>>>          return buf
>>>     # TODO: add pythonization API to pypy-c
>>>          cppyy.add_pythonization(
>>>             cppyy.compose_method("^TGraph(2D)?$|^TGraph.*Errors$",
>>> "GetE?[XYZ]$", set_size))
>>> The functions selected by the regexps return naked pointers, but the object
>>> can be queried for the size (all have a consistent GetN() function). So the
>>> method composer patches up the return value, making it a sized array,
>>> instead of an "open-ended" one.
>>> I'm sitting on some patches as I wanted to tweak his APIs a bit. There
>>> was some ordering that I felt didn't compose well, but that is minor.
>>> Similarly, there's code to apply ownership rules, mapping exceptions,
>>> the new C++11 smartptrs, controlling auto-casting, handling the GIL, making
>>> properties, and adding overloads. All driven by regexp matching of patterns.
>>> See here:
>>> https://bitbucket.org/wlav/cppyy/src/4d14ba325e494f13cc11f3f11cbb87b44048b256/python/cppyy/_pythonization.py?at=master
>>> (plus further support inside the bindings layer itself).
>>> Of course, one can hook up completely custom functions, and he made it so
>>> that that is per C++ namespace, so nicely self-contained.
>>> Again, this is currently only partly available, as I need to write a lot
>>> more tests for PyPy (which are bound to unearth some problems along the
>>> way). And then there is documentation to be written ...
>>>> P.S. Please note that after today, I'll likely not have much Internet
>>>> access for a couple of weeks, so any responses may be limited.
>>> I'll make sure I have at least all my local changes pushed by then. :)
>>> Best regards,
>>>            Wim
>>> --
>>> WLavrijsen at lbl.gov    --    +1 (510) 486 6411    --    www.lavrijsen.net

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