Segmentation fault: Sewing

[e3dEF]

Hi,
I get a segmentation fault, when calling FreeEdge of a BRepBuilderAPI_Sewing() object using the current beta version (conda install, pythonocc-core 7.4.0beta2 py36h6bb024c_0). I tested also in 0.18.2 where it works.
Maybe you are aware of that fault already.

Here is the Dump of the sew:

 Number of input shapes      : 30
 Number of actual shapes     : 30
 Number of Bounds            : 86
 Number of Sections          : 86
 Number of Edges             : 65
 Number of Vertices          : 40
 Number of Nodes             : 40
 Number of Free Edges        : 56
 Number of Contigous Edges   : 1
 Number of Multiple Edges    : 8
 Number of Degenerated Edges : 0

Here the result of 0.18.2

class<'TopoDS_Edge'; id:2042279761>
class<'TopoDS_Edge'; id:2042253057>
class<'TopoDS_Edge'; id:2042258465>
...

[tpaviot]

Can you please give any clue to reproduce the issue ?

[e3dEF]

I think I found MY mistake. I tried to access the edges in range(sew.NbFreeEdges()). Instead, I have to loop in range(1, sew.NbFreeEdges() + 1). The difference between 0.18.2 and 7.4 was that 0.18.2 gave a RuntimeError: Standard_OutOfRange that was caught by a try statement. 7.4. raised the segmentation fault.

[rainman110]

@tpaviot A segfault should never occur. Instead pythonocc should catch the c++ exception and convert it to a runtime error.

[rainman110]

@e3dEF What OS are you using? I noticed some problems wrt exception handling on macos.

[tpaviot]

@rainman110 pythonocc only catches occt exceptions. But if occt fails without raising any exception (i.e. occt segfaults), then pythonocc will segfault as well. That is to say that, if pythonocc segfaults, then it comes from an uncatched occt exception and should be reported upstream. As far as I know, catching occt exception works quite well: all calls to occt methods are put within a try/catch block (see https://github.com/tpaviot/pythonocc-core/blob/master/src/SWIG_files/common/ExceptionCatcher.i)

[tpaviot]

@e3dEF just to check, can you please post the code you've been testing with ?

[rainman110]

@tpaviot the pythonocc exception catcher is correct. The problems I noticed is a macos / compiler specific thing than also happens on other pure c++ code.

From what I have seen, it seems to happen when using the conda-build compiler.

[adam-urbanczyk]

@rainman110 maybe it's just noise but I have seen similar issues when doing custom builds on older PythonOCC versions too CadQuery/cadquery#207 . I know too little about MacOS to figure that one out.

[e3dEF]

My OS is Ubuntu 18.04.
Here is the code

from OCC.Core.BRepTools import breptools_Read
from OCC.Core.TopoDS import TopoDS_Shape
from OCC.Core.BRep import BRep_Builder
from OCC.Core.BRepBuilderAPI import BRepBuilderAPI_Sewing

sew = BRepBuilderAPI_Sewing()

for i in range(2):
    shape = TopoDS_Shape()
    builder = BRep_Builder()
    breptools_Read(shape, str(i) + ".brep", builder)
    sew.Add(shape)

sew.Perform()
sew.Dump()

print(sew.FreeEdge(0))

The opened breps are 2 planar faces. I could provide the files, if necessary (3kB).

Dump:

 ===========================================================
 
 Number of input shapes      : 2
 Number of actual shapes     : 2
 Number of Bounds            : 9
 Number of Sections          : 9
 Number of Edges             : 9
 Number of Vertices          : 9
 Number of Nodes             : 9
 Number of Free Edges        : 9
 Number of Contigous Edges   : 0
 Number of Multiple Edges    : 0
 Number of Degenerated Edges : 0
 ===========================================================

sew.SewedShape():

[tpaviot]

@adam-urbanczyk @rainman110 Exception handling is unittested, see https://github.com/tpaviot/pythonocc-core/blob/master/test/core_wrapper_features_unittest.py#L490 If necessary, I can extend the number of tests, but they actually pass on all platforms.

@e3dEF Yes, please, can you attach brep files as well

[e3dEF]

Files:
BREPs.zip

[tpaviot]

Here is the result on my machine:

                        Informations                        
 ===========================================================
 
 Number of input shapes      : 2
 Number of actual shapes     : 2
 Number of Bounds            : 9
 Number of Sections          : 9
 Number of Edges             : 9
 Number of Vertices          : 9
 Number of Nodes             : 9
 Number of Free Edges        : 9
 Number of Contigous Edges   : 0
 Number of Multiple Edges    : 0
 Number of Degenerated Edges : 0
 ===========================================================
 
Erreur de segmentation (core dumped)

I looked at the c++ code, an exception should be raised/catched (from BRepBuilderAPI_Sewing.cxx):

//=======================================================================
//function : FreeEdge
//purpose  : 
//=======================================================================

const TopoDS_Edge& BRepBuilderAPI_Sewing::FreeEdge(const Standard_Integer index) const
{
  Standard_OutOfRange_Raise_if(index < 0 || index > NbFreeEdges(), "BRepBuilderAPI_Sewing::FreeEdge");
  return TopoDS::Edge(myFreeEdges(index));
}

The Standard_OutOfRange_Raise_if macro is defined in Standard_OutOfRange.hxx, see:

#if !defined No_Exception && !defined No_Standard_OutOfRange
  #define Standard_OutOfRange_Raise_if(CONDITION, MESSAGE) Standard_OutOfRange_Always_Raise_if(CONDITION, MESSAGE)
#else
  #define Standard_OutOfRange_Raise_if(CONDITION, MESSAGE)
#endif

My feeling is that the occt exception is not raised, @rainman110 your opinion ?

[rainman110]

Just looking at this occt c++ code. Shouldn't it be
index<1 ? I think we found our bug.