[pypy-dev] cpyext: Detecting pypy and other issues

[Roger Binns]

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I'm trying to port my APSW C extension to pypy and am encountering various
issues.  APSW is somewhat similar to pysqlite in that it wraps SQLite, but
APSW wraps all of SQLite and provides SQLite's semantics rather than
whatever DBAPI says.  APSW supports Python 2.3 through 3.2.

What is the correct way to detect pypy compilation?  My code includes
various enhancements and optimisations but they depend on CPython to some
degree.  These would need to be disabled at compile time.  It looks like
PYPY_VERSION being #defined will work but I'd rather use the "official" way
whatever that is.

One example optimisation I do is object reuse.  When the refcount is 1 and
it is dealloc then they go to a recycle list.  Doing this gave several
percentage point performance improvements.  This can be disabled with a #define.

An example of enhanced functionality is an alternative to
PyErr_WriteUnraiseable.  The CPython implementation is virtually useless (eg
no traceback).  My version shows the traceback but again depends on CPython
internals to get it.

 http://code.google.com/p/apsw/source/browse/src/util.c#89

I need the api PyRun_StringFlags as it is used to execute a Python string
and attach the results to the module.  It is called like this:

 PyRun_StringFlags(char*, Py_file_input, apswdict, apswdict, NULL);

I do have a benchmarking tool that mainly exposes the performance
improvement of APSW over pysqlite.  Most of the work of the wrapper is
taking Python types (especially strings) and providing them to the SQLite
APIs, and getting data back from SQLite and converting back to Python types.
 There is a lot of GIL acquisition and release.  In order to improve
performance there are also various string related caches.  My test suite has
99,6% coverage of the C code so I should be able to find all the places
where pypy differs.

Roger
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