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

Charles R Harris charlesr.harris@gmail....
Fri Jul 18 22:49:23 CDT 2008


On Fri, Jul 18, 2008 at 9:30 PM, Travis E. Oliphant <oliphant@enthought.com>
wrote:

> Charles R Harris wrote:
> >
> >
> > The reference leak seems specific to the float32 and complex64 types
> > called with default arguments.
> >
> > In [1]: import sys, gc
> >
> > In [2]: t = float32
> >
> > In [3]: sys.getrefcount(dtype(t))
> > Out[3]: 4
> >
> > In [4]: for i in range(10) : t();
> >    ...:
> >
> > In [5]: sys.getrefcount(dtype(t))
> > Out[5]: 14
> >
> > In [6]: for i in range(10) : t(0);
> >    ...:
> >
> > In [7]: sys.getrefcount(dtype(t))
> > Out[7]: 14
> >
> > In [8]: t = complex64
> >
> > In [9]: sys.getrefcount(dtype(t))
> > Out[9]: 4
> >
> > In [10]: for i in range(10) : t();
> >    ....:
> >
> > In [11]: sys.getrefcount(dtype(t))
> > Out[11]: 14
> >
> > In [12]: t = float64
> >
> > In [13]: sys.getrefcount(dtype(t))
> > Out[13]: 19
> >
> > In [14]: for i in range(10) : t();
> >    ....:
> >
> > In [15]: sys.getrefcount(dtype(t))
> > Out[15]: 19
> >
> > This shouldn't actually leak any memory as these types are singletons,
> > but it points up a logic flaw somewhere.
> >
> That is correct.   There is no memory leak, but we do need to get it
> right.  I appreciate the extra eyes on some of these intimate details.
> What can happen (after a lot of calls) is that the reference count can
> wrap around to 0 and then cause a funny dealloc (actually, the dealloc
> won't happen, but a warning will be printed).
>
> Fixing the reference counting issues has been the single biggest
> difficulty in converting PyArray_Descr from a C-structure to a regular
> Python object.  It was a very large pain to begin with, and then there
> has been more code added since the original conversion some of which
> does not do reference counting correctly (mostly my fault).
>
> I've looked over ticket #848 quite a bit and would like to determine the
> true cause of the growing reference count which I don't believe is fixed
> by the rest of the patch that is submitted there.
>

I've attached a test script.

Chuck
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