Bug when creating vector object in prange loop

[Markus Brachner]

I think I found some bug.

I use the current release version of Cython 0.22.1

For me this minimal example leads to a compilation error:

from cython.parallel import prange

from libcpp.vector cimport vector

ctypedef vector[float] pointvector

        

def test_parallel():

    cdef Py_ssize_t j

    cdef pointvector *pv

    

    for j in prange(0,10,nogil=True):

        pv = new pointvector()

The problem is the creation of the pointvector object with the libcpp vector. In a normal range loop the same compiles fine with Cython. It works fine with prange, if I use my own vector wrapper:

cdef extern from "<vector>" namespace "std":

    cpdef cppclass vector[T]:

        cppclass iterator:

            T operator*()

            iterator operator++()

            bint operator==(iterator)

            bint operator!=(iterator)

        vector() nogil

        void push_back(T&) nogil

        T& operator[](int)

        T& at(int)

        iterator begin()

        iterator end()

Can sombebody reproduce this?

[Stefan Behnel]

You didn't say what the problem is, but my guess is that the error you get
is that Cython refuses to compile code that raises Python exceptions in a
nogil block. In your vector declaration, you are instructing Cython to not
catch C++ exceptions (and convert them to Python exceptions), i.e. you'd
most likely get a crash if allocating the "pointvector" instance fails. So
yes, there is a bug in your code. :)

How to deal with this depends on your actual code, though. You could catch
the exception in a "with gil" block, or you could allocate the C++ objects
outside of the nogil loop, or ...

Stefan

[Markus Brachner]

Thanks for your answer Stefan. As I mentioned I get a compilation error. To be more specific: gcc output is

gcc.exe -DMS_WIN64 -mdll -O -Wall -IC:\Anaconda3\envs\py27\lib\site-packages\num

py\core\include -IC:\Anaconda3\envs\py27\include -IC:\Anaconda3\envs\py27\PC -c

c:\tmp\opentest.cpp -o c:\tmp\opentest.o

c:\tmp\opentest.cpp: In function 'PyObject* __pyx_pf_8opentest_test_parallel(PyO

bject*)':

c:\tmp\opentest.cpp:685:68: error: invalid conversion from 'int' to '__pyx_t_8op

entest_pointvector* {aka std::vector<float>*}' [-fpermissive]

             __pyx_t_8opentest_pointvector * __pyx_parallel_temp0 = 1;

                                                                    ^

error: command 'gcc.exe' failed with exit status 1

This is a minimal example, thus I don't do any error handling. It does not even compile. I mentioned also, that wrapping the vector class works by my own works around the problem. In this case it runs without crashing.

Best,

Markus