Hi Thomas
Well, I'm glad it's not a bug then! I can think of a few ways to handle
this situation in my algorithm, so it should not be a problem. I'm just
wondering how many other classes behave in this "unexpected" way :O
Cheers,
Frank
On 15/03/2010 10:26 PM, Thomas Paviot wrote:
Hi Frank,
This behaviour does not come from SWIG but from OpenCASCADE itself.
Let me explain you in a few words what happens here.
The BRepPrimAPI_MakeBox class inherits from the
BRepBuilderAPI_MakeShape one. This class provides the Shape() method
you can find in BRepPrimAPI_Make* basic geometry constructors. If you
have a look at the Shape() method in the file
BRepBuilderAPI_MakeShape.cxx, you will read:
"""
//=======================================================================
//function : Shape
//purpose :
//=======================================================================
const TopoDS_Shape& BRepBuilderAPI_MakeShape::Shape() const
{
if (!IsDone()) {
// the following is const cast away
((BRepBuilderAPI_MakeShape*) (void*) this)->Build();
Check();
}
return myShape;
}
"""
The Shape() method then returns a reference to the protected attribute
'myShape' of the class BRepBuilderAPI_MakeBox. In other words, if you
delete the BRepPrimAPI_MakeBox instance, you loose the reference to
the shape.
For instance:
>>> from OCC.BRepPrimAPI_MakeBox import *
>>> from OCC.TopoDS import *
>>> box = BRepPrimAPI_MakeBox(10,10,10)
>>> shp = box.Shape()
>>> print shp.IsNull()
0
>>> del box #object is garbage collected, not deleted yet
>>> print shp.IsNull()
0
>>> GarbageCollector.garbage.smart_purge() # all objects are deleted,
loose the reference to myShape attribute
>>> print shp.IsNull()
1
Then force objects deletion only if you're sure you don't need the
shapes anymore. I don't know what you're trying to do exactly, so it's
difficult to suggest any best practice.
Regards,
Thomas
2010/3/15 Frank Conradie <fr...@qfin.net <mailto:fr...@qfin.net>>
Hi Thomas
I am getting crash behaviour in the interim 0.5 PythonOCC release,
related to the new GarbageCollector implementation. The code below
crashes on my PC:
----------------------------------------
from OCC.gp import *
from OCC.BRepPrimAPI import *
from OCC.BRepBuilderAPI import *
from OCC.TopExp import *
from OCC.TopoDS import *
o = 0.0
w = 0.1
fp1 = (o,o,o)
fp2 = (w,w,w)
mkbox = BRepPrimAPI_MakeBox(gp_Pnt(fp1[0],fp1[1],fp1[2]),
gp_Pnt(fp2[0],fp2[1],fp2[2]))
s = mkbox.Shape()
del mkbox
print s.ShapeType()
GarbageCollector.garbage.smart_purge()
# The next line crashes my system
print s.ShapeType()
----------------------------------------
It is almost as if calling _kill_pointed for the mkbox causes
shape "s"
to become "corrupted" in some way. I dug through the SWIG code a bit,
but cannot see anything obviously wrong, so I was hoping you could
shed
some light on the issue.
By the way, I did get the SVN compiled myself as well, and get the
same
crash with my compiled lib as well as the one you made available
on your
website.
Thanks,
Frank
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