通过使用回调在Cython代码中封装C库（GSL）

Question

我刚接触 cython 和 c，想用 cython 来加速我的代码性能。我想在我的代码中使用 gsl_integration 库来进行积分。

更新：test_gsl.pyx

cdef extern from "math.h":
    double log(double x) nogil
cdef extern from "gsl/gsl_math.h":
    ctypedef struct gsl_function:
        double (* function) (double x, void * params)
        void * params

cdef extern from "gsl/gsl_integration.h":
    ctypedef struct gsl_integration_workspace
    gsl_integration_workspace *  gsl_integration_workspace_alloc(size_t n)
    void  gsl_integration_workspace_free(gsl_integration_workspace * w)

    int  gsl_integration_qags(const gsl_function * f, double a, double b, double epsabs, double epsrel, size_t limit, gsl_integration_workspace * workspace, double *result, double *abserr)


cdef double do_callback(double x, void* params):
    return (<MyCallback>params).eval(x)

cdef class MyCallback:
    cdef double a
    def __init__(self, a):
        self.a = a
    cpdef double eval(self, double x):
        return self.a * log(x+1) * x
    def call_gsl(self):
        cdef gsl_integration_workspace* w =gsl_integration_workspace_alloc (1000)

        cdef gsl_function F
        F.function = &do_callback
        F.params = <void*>self

        cdef double result = 3, error = 5
        gsl_integration_qags(&F, 0, 1, 0, 1e-7, 1000, w, &result, &error)
        print result, error
        gsl_integration_workspace_free(w)

这个 .pyx 文件是用下面的 setup.py 文件编译的，并且没有出现任何错误信息：

from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
import numpy
import sys 
ext = Extension("test_gsl", ["test_gsl.pyx"],
    include_dirs=[numpy.get_include(),
                  "/usr/include/"],
    library_dirs=["/usr/lib/"],
    libraries=["gsl"])

setup(ext_modules=[ext],
    cmdclass = {'build_ext': build_ext})

甚至可以通过命令行来编译：

cython test_gsl.pyx
gcc -pthread -fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/vol/anaconda/lib/python2.7/site-packages -I/usr/include -I/vol/anaconda/include/python2.7 -c test_gsl.c `pkg-config --cflags gsl` 
gcc -pthread -shared test_gsl.o -L/usr/lib -L/vol/anaconda/lib -lgsl -lgslcblas -lpython2.7 `pkg-config --libs gsl` -o test_gsl.so

但是当在 Python 中这样导入时，却出现了错误：

>>> import pyximport; pyximport.install()
(None, <pyximport.pyximport.PyxImporter object at 0x7f0c7e888150>)
>>> import gsl
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/anaconda/lib/python2.7/site-packages/Cython-0.20.1-py2.7-linux-x86_64.egg/pyximport/pyximport.py", line 431, in load_module
    language_level=self.language_level)
  File "/anaconda/lib/python2.7/site-packages/Cython-0.20.1-py2.7-linux-x86_64.egg/pyximport/pyximport.py", line 210, in load_module
    mod = imp.load_dynamic(name, so_path)
ImportError: Building module gsl failed: ['ImportError: /users/dalek/.pyxbld/lib.linux-x86_64-2.7/gsl.so: undefined symbol: gsl_integration_qags\n']

gsl_integration_qags 已经正确定义了，我不明白为什么还会出现这个错误？

代码性能 cython 积分 C++库回调 gsl

通过使用回调在Cython代码中封装C库（GSL）

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