On Thu, 30 May 2013 17:23:39 +0600, Marin Atanasov Nikolov
<dna...@gmail.com> wrote:
Hello,
First, apologies if this is not exactly the right place to post this,
but I
have tried already cython-users@ and my post is still pending somewhere
for approval, so I've decided to give it a shot here.
I'm working on Cython wrappers for a C library and everything was going
smooth on my dev machine, until I've decided to install the wrappers on
another machine.
The only difference between these machines is that my dev machine has
Python built with debug symbols and the other machine does not have debug
symbols in Python.
The issue I'm having and was trying to solve for the past few days is
that
if I run my Cython wrappers on a machine where Python does not have debug
symbols it core dumps ugly. If I run the same code on another machine
with
Python + debug symbols then everything is running perfect.
I've done some debugging and tracing as well, and noticed that the core
dump happens at PyTuple_Size() when I have Python *without* debug
symbols.
Running Python + debug symbols shows that the interpreter takes a
different path and does not core dump (does not even call PyTuple_Size()
for some reason)
Anyway, I've uploaded the backtrace and some gdb tracing in here:
* http://users.unix-heaven.org/~dnaeon/cython-wrappers/wrappers-trace.txt
The code that I have you can find in here:
* http://users.unix-heaven.org/~dnaeon/cython-wrappers/src/
What really puzzles me is why it core dumps when Python does not have
debug
symbols and why it takes a different path (and not core dumping) when
Python is built with debug symbols.
I'd say that if it core dumps because of a NULL pointer or something
similar, then having Python with or without debug symbols should not
make a
difference, but it does for some reason.
I've been working on this for the past few days and I'm out of ideas now.
Any help/hints/feedback is much appreciated.
In pkg-db.pxi, this line:
return Pkg(<object>pkg)
and in pkg-pkg.pxi this line:
def __cinit__(self, pkg):
self._pkg = <c_pkg.pkg *>pkg
are the problem.
You are trying to pass a C pointer to __cinit__. What actually
happens is that, because of the <object> cast, Cython treats pkg as
as Python object _itself_ and tries to do some object operations on it.
Two ways to solve this (really common) problem:
1) Pass your pointer as a real python object containing the integer value
of the pointer:
def __cinit__(self, pkg):
self._pkg = <c_pkg.pkg *><Py_ssize_t>pkg # or Py_intptr_t
return Pkg(<object><Py_ssize_t>pkg)
Note the <Py_ssize_t> cast. When used on a C pointer, it makes a C
integer that Cython convert to python int object. And when <Py_ssize_t>
is used on a python int object, Cyton extracts its integer value
as a C-level value, so it is castable to a C-level pointer.
Using Py_ssize_t (or Py_intptr_t or your platform intptr_t) guarantees
that the pointer will fit.
2) Don't use __cinit__. Declare your own cdef init method and call that.
Since it's cdef method, it can take any C-level arguments, pointerw,
whatever without the need to convert to python objects and back.
@cython.final # small optimization
cdef _init(self, c_pkg.pkg * pkg):
self._pkg = pkg
# cdef __cinit__ not needed. Maybe use it to set default
# attribute values.
cdef Pkg pkg = Pkg.__new__(Pkg) # fast object creation. Pkg() also
works.
pkg._init(pkg)
(When you use the __new__ trick, __cnit__ is called without
arguments and __init__ is not called at all. The benefit to
this ugly syntax is that __new__ is faster than creating the object
with traditional Pyhton syntax.)
Also, if all your initialization is pointer assigment, you can
just do it directly:
cdef Pkg pkg = Pkg.__new__(Pkg) # fast object creation
pkg._pkg = pkg
There is a problem related to cython-dev. I think the code you
wrote should have never compiled in the first place. <PyObject*>
cast must be required if you want to reinterpret a C pointer
as object or vice versa.
Best regards,
Nikita Nemkin
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