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Date: Tue, 20 Dec 2011 19:39:06 +0100
From: Dag Sverre Seljebotn <d.s.seljeb...@astro.uio.no>
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Subject: Differences between C++ Cython wrapper and C++ program
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Hi list,

I'm trying to wrap a proprietary, closed-source C++ library using 
Cython. The library essentially fails to work when used through a Cython 
wrapper, but works when compiling as a standalone executable with the 
same compiler flags.

I.e., I have a function "foomain" with some C++ code which attempts to 
make a certain network connection. If I call foomain() from main() in a 
C++ program, things work. If I call foomain() from Cython, compiled in 
C++ mode, then things don't work (no connection is made).

So what are the possible differences in the runtime environment you can 
think of?

The first thing I had to do was this:

import sys, ctypes
sys.setdlopenflags(sys.getdlopenflags()|ctypes.RTLD_GLOBAL)

This fixed something else (a function mysteriously returning a NULL 
pointer when it shouldn't -- as I don't have the sources I don't know 
why, really). But apparently it didn't fix everything.

I've tried both with and without creating a thread using the threading 
module (so that a GIL is set up), and both with and without "with nogil" 
around the call to foomain().


Dag Sverre