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Fix Python crash when using -threads iterating containers

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Also fixes li_std_vector_enum testcase when run with -threads.

Patch supplied on swig-devel mailing list on 12 Sep with details...

==============================================
I just wanted to mention that I found a crash issue in bug..

I am using SWIG 2.0.11 with python and have –threads enabled.  I have a C++ std::vector that I instantiate in SWIG with %template.  I also have a method in a class that returns this vector.  I also include std_vector.i, btw..

When I iterate like so:

children = Action.getActionList()
for child in children:
  pass

Everything is fine..

When I iterate like this:

for child in Action.getActionList()
  pass

Product crashes.

The problem is the following.  This code gets called first:

SWIGINTERN PyObject *_wrap_delete_SwigPyIterator(PyObject *SWIGUNUSEDPARM(self), PyObject *args) {
  PyObject *resultobj = 0;
  swig::SwigPyIterator *arg1 = (swig::SwigPyIterator *) 0 ;
  void *argp1 = 0 ;
  int res1 = 0 ;
  PyObject * obj0 = 0 ;

  if(!PyArg_UnpackTuple(args,(char *)"delete_SwigPyIterator",1,1,&obj0)) SWIG_fail;
  res1 = SWIG_ConvertPtr(obj0, &argp1,SWIGTYPE_p_swig__SwigPyIterator, SWIG_POINTER_DISOWN |  0 );
  if (!SWIG_IsOK(res1)) {
    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "delete_SwigPyIterator" "', argument " "1"" of type '" "swig::SwigPyIterator *""'");
  }
  arg1 = reinterpret_cast< swig::SwigPyIterator * >(argp1);
  {
    SWIG_PYTHON_THREAD_BEGIN_ALLOW;
    delete arg1;
    SWIG_PYTHON_THREAD_END_ALLOW;
  }
  resultobj = SWIG_Py_Void();
  return resultobj;
fail:
  return NULL;
}

Note the SWIG_PYTHON_THREAD_BEGIN_ALLOW/END_ALLOW. In between those two statements, we delete arg1.  That in turn will eventually end up in this code:

namespace swig {
  class SwigPtr_PyObject {
  protected:
    PyObject *_obj;

  public:
    … snip! …
    ~SwigPtr_PyObject()
    {
      Py_XDECREF(_obj);
    }

Uh-oh!  We call Py_XDECREF when we aren’t supposed to because we are in a SWIG_PYTHON_THREAD_BEGIN_ALLOW/END_ALLOW section!

This takes care of the issue:

namespace swig {
  class SwigPtr_PyObject {
  protected:
    PyObject *_obj;

  public:
    … snip! …
    ~SwigPtr_PyObject()
    {
      SWIG_PYTHON_THREAD_BEGIN_BLOCK;
      Py_XDECREF(_obj);
      SWIG_PYTHON_THREAD_END_BLOCK;
    }

There are several other methods in this class that use the Python API, but don’t have the BEGIN/END block defined.  I’m not sure if they are required for all of them, but I believe they are..

I have attached a modified pyclasses.swg with what I believe are the correct changes.  This code is from 2.0.11, but as far as I can tell, it’s the same as what is in 3.0.2…

Apologies for not doing more here (making/running tests, getting it in the code repository, etc..), but I’m under some pressure to get some unrelated things done…
This commit is contained in:
Thomas Maslach 2014-09-23 20:22:20 +01:00 • committed by William S Fulton
commit de6b433cb1
4 changed files with 62 additions and 0 deletions
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8
Lib/python/pyclasses.swg
View file

@ -72,27 +72,35 @@ namespace swig {
SwigPtr_PyObject(const SwigPtr_PyObject& item) : _obj(item._obj)
{
SWIG_PYTHON_THREAD_BEGIN_BLOCK;
Py_XINCREF(_obj);
SWIG_PYTHON_THREAD_END_BLOCK;
}
SwigPtr_PyObject(PyObject *obj, bool initial_ref = true) :_obj(obj)
{
if (initial_ref) {
SWIG_PYTHON_THREAD_BEGIN_BLOCK;
Py_XINCREF(_obj);
SWIG_PYTHON_THREAD_END_BLOCK;
}
}
SwigPtr_PyObject & operator=(const SwigPtr_PyObject& item)
{
SWIG_PYTHON_THREAD_BEGIN_BLOCK;
Py_XINCREF(item._obj);
Py_XDECREF(_obj);
_obj = item._obj;
SWIG_PYTHON_THREAD_END_BLOCK;
return *this;
}
~SwigPtr_PyObject()
{
SWIG_PYTHON_THREAD_BEGIN_BLOCK;
Py_XDECREF(_obj);
SWIG_PYTHON_THREAD_END_BLOCK;
}
operator PyObject *() const