dolfin team mailing list archive

[Garth Wells <747289@xxxxxxxxxxxxxxxxxx>]

On 22/04/11 16:41, Johan Hake wrote:
> The C++ Director class, which inherits Expression is not destroyed, as
> this is stored using shared_ptr. Just put in a print in the destructor
> of Expression and you will see that it is not prematurely destroyed.
> However, what is destroyed is the Python proxy class, which eventually
> receives the callback. I am not sure why this whole thing doesn't just
> crash, but then the SWIG Directory code probably take care of this
> situation.
> 

I traced this through the C++ code, and concluded the same thing (but
less elegantly).

> Joachim's patch fixes this problem. I think it is ok to apply the patch.
> We need to go over what other places this problem might be a problem.
> 
> Once you think you sorted out things using shared_ptrs, this turns up...
> 

It turns out that one of the objects that the Python DirichletBc class
stored no longer has to be stored thanks to the smart pointers ;).

Garth

> Johan
>

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https://bugs.launchpad.net/bugs/747289

Title:
  Python: DirichletBC arguments are deleted early

Status in DOLFIN:
  Confirmed

Bug description:
  The following code fails with a strange error:
  -----
  from dolfin import *
  class Boundary(SubDomain):
      def inside(self, x, on_boundary):
          return on_boundary
  class BoundaryFunction(Expression):
      def eval(self, values, x):
          values[0] = 1 if near(x[1],1) else 0
  mesh = UnitSquare(2,2)
  V = FunctionSpace(mesh, "CG", 1)
  v,u = TestFunction(V), TrialFunction(V)
  A = assemble(v*u*dx)

  bc = DirichletBC(V, BoundaryFunction(), Boundary())
  bc.apply(A)
  -----
  Replacing the bc = line as follows also fails, with a different strange error:
  -----
  bf = BoundaryFunction()
  bc = DirichletBC(V, BoundaryFunction(), Boundary())
  ----
  Only this works:
  -----
  bf = BoundaryFunction()
  bc = DirichletBC(V, bf, Boundary())
  -----

  I have attached a patch that works around this by saving a reference
  to the arguments in DirichletBC. It's not the proper fix of course,
  but I have no time to find the root cause.