dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Oct 31, 2007 at 10:10:42AM +0100, Martin Sandve Alnæs wrote:
> 2007/10/31, Martin Sandve Alnæs <martinal@xxxxxxxxx>:
> > 2007/10/30, Ola Skavhaug <skavhaug@xxxxxxxxx>:
> > > Anders Logg skrev den 30/10-2007 følgende:
> > > > The following code gives me a segmentation fault:
> > > >
> > > >   from dolfin import *
> > > >
> > > >   def foo():
> > > >       element = FiniteElement("Lagrange", "triangle", 1)
> > > >       mesh = UnitSquare(2, 2)
> > > >       return Function(element, mesh, 1.0)
> > > >
> > > >   print foo().mesh().numVertices()
> > > >
> > > > If the mesh is declared outside foo() it works fine.
> > > >
> > > > It seems that Python is calling the Mesh destructor when foo()
> > > > returns. It shouldn't since the Function created in foo() keeps a
> > > > reference to the mesh.
> > > >
> > > > Does anyone know how to fix this? Is it possible to tell Python that
> > > > the mesh is referenced by the function?
> > >
> > > Take a look at the swig documentation. It might be possible to add some
> > > directives for this, but it is a major problem. Even the Python bindings for
> > > vtk have this flaw.
> >
> > This is also the same as the memory handling issues we haven't given
> > any serious thought in the GenericTensor hierarchy: A = Matrix();
> > assemble(A); A = A.mat(); who owns the underlying PetSCMatrix or
> > EpetraMatrix now?
> >
> > If you can accept a common base class with a reference count for all
> > dolfin classes, and using str::tr1::shared_ptr in the C++ code, it can
> > be solved (at least for most use cases).
> 
> Sorry, that won't work for the linear algebra classes, because it
> would require a reference count located in the Mat object (with
> PetSC).

The PETSc Mat pointer is created in the constructor of
dolfin::PETScMatrix and destroyed in the destructor so we have full
control over it.

What is str::tr1::shared_ptr???

/Anders


> You can still solve it for the classes you have full control over in
> dolfin though.