[Numpy-discussion] Ticket review: #848, leak in PyArray_DescrFromType

[Travis E. Oliphant]

Charles R Harris wrote:
>
>
> On Fri, Jul 18, 2008 at 9:15 PM, Travis E. Oliphant 
> <oliphant at enthought.com <mailto:oliphant at enthought.com>> wrote:
>
>     Michael Abbott wrote:
>     > Only half of my patch for this bug has gone into trunk, and
>     without the
>     > rest of my patch there remains a leak.
>     >
>     Thanks for your work Michael.   I've been so grateful to have you and
>     Chuck and others looking carefully at the code to fix its problems.
>
>     In this particular case, I'm not sure I see how (the rest of) your
>     patch
>     fixes any remaining leak.   We do seem to be having a disagreement
>     about
>     whether or not the reference to typecode can be pre-maturely
>     destroyed,
>     but this doesn't fit what I usually call a "memory leak."     I think
>     there may be some other cause for remaining leaks.
>
>
> Travis,
>
> There really is (at least) one reference counting error in 
> PyArray_FromAny. In particular, the obj == NULL case leaves a 
> reference to typecode, then exits through the first return after 
> finish. In this case robj doesn't steal a reference to typecode and 
> the result can be seen in the python program above or by printing out 
> the typecode->ob_refcnt from the code itself. So that needs fixing. I 
> would suggest a DECREF in that section and a direct return of robj.
agreed!  I'll commit the change.
>
> The next section before finish is also a bit odd. The direct return of 
> an array works fine, but if that isn't the branch taken, then 
> PyArray_Return decrements the refcnt of arr, which in turn decrements 
> the refcnt of typecode. I don't know if the resulting scalar holds a 
> reference to typecode, but in any case the situation there should also 
> be clarified.
This looks fine to me.   At the PyArray_Return call, the typecode 
reference is held by the array.  When it is decref'd the typecode is 
decref'd appropriately as well.   The resulting scalar does *not* 
contain a reference to typecode.  The scalar C-structure has no place to 
put it (it's just a PyObject_HEAD and the memory for the scalar value).

Michael is correct that PyArray_Scalar does not change the reference 
count of typecode (as the comments above that function indicates).  I 
tried to be careful to put comments near the functions that deal with 
PyArray_Descr objects to describe how they affect reference counting.  I 
also thought I put that in my book.

-Travis




-Travis