[Cython] [sage-devel] Re: Locally scoped dynamic memory (in SAGE and elsewhere)

[Brian Granger]

>  >  Lisandro Dalcin (author of mpi4py) came up with the following trick
>  >  that, while more complicated, prevents memory leaks:
>  >
>  >  cdef extern from "Python.h":
>  >     object PyString_FromStringAndSize(char*,Py_ssize_t)
>  >     char* PyString_AS_STRING(object)
>  >
>  >  cdef inline object pyalloc_i(int size, int **i):
>  >     if size < 0: size = 0
>  >     cdef Py_ssize_t n = size * sizeof(int)
>  >     cdef object ob = PyString_FromStringAndSize(NULL, n)
>  >     i[0] = <int*> PyString_AS_STRING(ob)
>  >     return ob
>  >
>  >  and now
>  >
>  >  def foo(sequence):
>  >     cdef int size = len(sequence),
>  >     cdef int *buf = NULL
>  >     cdef object tmp = pyalloc_i(size, &buf)
>  >
>  >  This could probably be adapted into a malloc-like function.  What do
>  >  people think?
>
>  Could you explain what the point is?  Is it that this is a trick so that
>  Cython will correctly garbage collect the allocated memory, even
>  if an exception occurs?

Yes, that is the idea.  By having a python object that knows about the
memory, the garbage collection should prevent memory leaks if an
exception occurs.  I am not sure if Lisandro has proved that this is
the case - he is just wondering how people typically handle this case.

Seems like we are not alone in thinking this is a problem though.

Brian

>   -- William
>
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