[Numpy-discussion] PyArray_SimpleNewFromData segfaults

[Ondrej Certik]

On Mon, Oct 5, 2009 at 8:38 PM, Ondrej Certik <ondrej@certik.cz> wrote:
> On Mon, Oct 5, 2009 at 7:34 PM, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
>>
>>
>> On Mon, Oct 5, 2009 at 7:40 PM, Ondrej Certik <ondrej@certik.cz> wrote:
> [...]
>>> still alive
>>> Segmentation fault
>>>
>>>
>>>
>>> What puzzles me is that there is no debugging print statement just
>>> before the segfault.
>>
>> Maybe you need to flush the buffer. That is a good thing to do when
>> segfaults are about.
>
> I tried to put "fflush(NULL);" after it, but it didn't help. I have
> created a super simple demo for anyone to play:
>
>
> $ git clone git://github.com/certik/segfault.git
> $ cd segfault/
> $ vim Makefile     # <-- edit the python and numpy include paths
> $ make
> $ python test.py
> I am still alive
> Segmentation fault
>
> where test.py is:
>
> $ cat test.py
> import _hermes1d
> v = _hermes1d.test()
> print v
>
>
> and _hermes1d.pyx is:
>
> $ cat _hermes1d.pyx
> def test():
>    cdef npy_intp size
>    cdef ndarray newarr
>    cdef double *arrsource
>
>    size = 10
>    arrsource = <double *>malloc(sizeof(double) * size)
>    print "I am still alive"
>    newarr = PyArray_SimpleNewFromData(1, &size, NPY_DOUBLE, <void *>arrsource)
>    print "I am dead."
>
>    return newarr
>
>
> So I bet there is something very stupid that I am missing. Still
> investigating...

I didn't call _import_array()  !

This patch fixes it:


diff --git a/_hermes1d.pxd b/_hermes1d.pxd
index 9994c28..f5e8868 100644
--- a/_hermes1d.pxd
+++ b/_hermes1d.pxd
@@ -54,6 +54,8 @@ cdef extern from "arrayobject.h":
     object PyArray_SimpleNewFromData(int nd, npy_intp* dims, int typenum,
             void* data)

+    void _import_array()
+
 cdef extern from "Python.h":
     ctypedef void PyObject
     void Py_INCREF(PyObject *x)
diff --git a/_hermes1d.pyx b/_hermes1d.pyx
index e542ddc..7a4beec 100644
--- a/_hermes1d.pyx
+++ b/_hermes1d.pyx
@@ -2,6 +2,7 @@ def test():
     cdef npy_intp size
     cdef ndarray newarr
     cdef double *arrsource
+    _import_array()

     size = 10
     arrsource = <double *>malloc(sizeof(double) * size)




I think I learned something today the hard way.

Ondrej