[Swig-devel] [ swig-Bugs-1832054 ] %implicitconv can lead to a double free

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Bugs item #1832054, was opened at 2007-11-14 16:10
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Category: python
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Robert Lupton the Good (rhl-astro)
Assigned to: Marcelo Matus (marcelomatus)
Summary: %implicitconv can lead to a double free

Initial Comment:
(Previously posted to swig-users)

I have a couple of problems with swig (1.3.31 or svn) related to
smart pointers;
both lead to a double free. This is C++/python.

I've appended a complete test case, but the basics are:
A simple C++ class Image defined in Image.h
a .i file saying:
%module badfree
...
%include "Image.h"
%template(ImagePtrT) boost::shared_ptr<Image >;

(The .i file needs its own version of boost::shared_ptr as
swig can't handle %include <boost::shared_ptr.hpp>, a problem
I've reported before but never resolved).

With this, the statements
import badfree
im = badfree.Image(10, 20)
iptr = badfree.ImagePtrT(im)
del im
del iptr

free the Image twice, as the ImagePtrT constructor doesn't realise
that python thinks that im still owns the object. I'm not exactly
sure that this is a bug, but it is a problem. It's one that I can
workaround by defining a macro that defines ImagePtrT() to disown im
(see appended .i file; one can also change the
boost::smart_ptr definition in the .i file), but
I think that this should be a swig macro not mine.

With this disown in place, the above code works just fine. But
if I add
%implicitconv boost::shared_ptr<Image>;
(directly or via %extend_smart_pointer) I get a double free again.
I don't know how to work around this one -- help!

R

------------------------------------------------------------------------
----------------badfree.i:
// -*- c++ -*-
%module badfree

%{
#include <boost/shared_ptr.hpp>

#include "Image.h"
%}

/*
* Don't expose the entire boost::shared_ptr to swig; it is
complicated...
*/
namespace boost {
template<class T>
class shared_ptr {
public:
// Copy constructor *must* come before the bare pointer
constructor. This is because a
// shared_ptr<T> * is convertible to a T * via
SWIG_ConvertPtr, so if the SWIG generated constructor
// argument dispatching function doesn't first test to see
if an incoming argument is a shared_ptr<T> *,
// double deletes will occur
shared_ptr(shared_ptr<T> const &);
shared_ptr(T *);
~shared_ptr();
T *operator->() const;
int use_count() const;
T *get() const;
};
}

%include "Image.h"

/
************************************************************************
******/
//
// Work around a swig 1.33.1 bug wherein swig doesn't realise that
python still
// owns the pointer that's now wrapped in a shared_ptr
//
%define smart_pointer(NAME, TYPE, PTR_TYPE)
// The next three lines are equivalent to %extend_smart_pointer
(PTR_TYPE<TYPE >);
%implicitconv PTR_TYPE<TYPE >;
%apply const SWIGTYPE& SMARTPOINTER { const PTR_TYPE<TYPE >& };
%apply SWIGTYPE SMARTPOINTER { PTR_TYPE<TYPE > };

%template(NAME) PTR_TYPE<TYPE >;

#if 1
%extend PTR_TYPE<TYPE > {
%pythoncode %{
__oldInit__ = __init__
def __init__(self, *args):
args[0].this.disown()
self.__oldInit__(args[0])
%}
};
#endif
%enddef

%define boost_shared_ptr(NAME, TYPE)
smart_pointer(NAME, TYPE, boost::shared_ptr)
%enddef

/
************************************************************************
******/

boost_shared_ptr(ImagePtrT, Image);

%{
int Image::_gid = 0;

Image::Image(int nrow, int ncol) : _nrow(nrow), _ncol(ncol) {
_id = _gid++;
printf("In Image(): %d\n", _id);
}
Image::~Image() {
printf("In ~Image(): %d\n", _id);
}
%}

------------------------------------------------------------------------
----------------Image.h:
#include <boost/shared_ptr.hpp>

class Image {
public:
Image(int nrow, int ncol);
~Image();
int rows() const { return _nrow; }
int cols() const { return _ncol; }
int id() const { return _id; }
private:
int _nrow, _ncol;
int _id;
static int _gid;
};

------------------------------------------------------------------------
----------------Makefile (os/x):
#BOOST_DIR = /foo/bar/boost
COMMONFLAGS = -I$(BOOST_DIR)/include
CXXFLAGS = $(COMMONFLAGS) -fPIC -I. -I$(PYTHON_DIR)/include/python2.5
SWIGFLAGS = $(COMMONFLAGS) -c++ -python

SOFLAGS = -bundle -flat_namespace

_badfree.so : badfree_wrap.o
$(CC) -o _badfree.so $(SOFLAGS) badfree_wrap.o \
-L$(PYTHON_DIR)/lib/python2.5/site-packages -lpython

badfree_wrap.cc : badfree.i
swig $(SWIGFLAGS) -o badfree_wrap.cc badfree.i

clean :
$(RM) badfree.py *_wrap.* *.pyc *~ core.* *.o *.so

------------------------------------------------------------------------
----------------
demo.py:
#BOOST_DIR = /foo/bar/boost
COMMONFLAGS = -I$(BOOST_DIR)/include
CXXFLAGS = $(COMMONFLAGS) -fPIC -I. -I$(PYTHON_DIR)/include/python2.5
SWIGFLAGS = $(COMMONFLAGS) -c++ -python

SOFLAGS = -bundle -flat_namespace

_badfree.so : badfree_wrap.o
$(CC) -o _badfree.so $(SOFLAGS) badfree_wrap.o \
-L$(PYTHON_DIR)/lib/python2.5/site-packages -lpython

badfree_wrap.cc : badfree.i
swig $(SWIGFLAGS) -o badfree_wrap.cc badfree.i

clean :
$(RM) badfree.py *_wrap.* *.pyc *~ core.* *.o *.so 

----------------------------------------------------------------------

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