Re: [IMP-dev] First significant code review

[Daniel Russel <>]

I gave up on reference counting as the existing swig support wasn't  
doing what we needed by itself. Getting things working right would not  
be too hard technically, but would take a bit of time and perhaps per- 
class entries in IMP.i.


Here is what I posted to the swig list. The only responses I got were  
"Yeah, that would be nice"

I would like to have reference counted objects that work across C++
and Python both for objects which are purely C++ objects and Python
objects which inherit from C++ base classes. This seems relatively
easily to implement by:
- Purely C++ objects or python objects extending C++ objects which
don't have virtual functions are just treated like they currently
are-- their reference count is incremented if there is a python
reference to them and decremented if there is no python reference. If
the python proxy object goes away before the C++ object, it is fine.
The C++ object can't go away without all python references being
destroyed.
- With Python objects which inherit from C++ objects with virtual
functions, swig has to keep the python proxy object alive until
the C++ object is destroyed. This can be done by internally keeping a
reference to the python object until the C++ object is destroyed.
Then the director can use the call to the virtual C++ destructor
(which needs  to be there on the C++ side anyway) to remove the
reference to the python object so that it too goes away.

While it is straight forward, I don't see any way to easily turn on
or provide this functionality for a large array of classes. I am
quite new to SWIG so I might be missing something.
Any suggestions or alternatives? Thanks.

On Dec 14, 2007, at 5:14 PM, Ben Webb wrote:

> Daniel Russel wrote:
> > DistanceRestraint now takes a pair of ParticleIndexes and a ScoreFunc
> > which it then owns.
>
> On this subject, did you make any more progress with the reference
> counting code? It seems like this would be a obvious candidate for
> reference counting (e.g. an excluded volume may create thousands of
> distance restraints, all of which share a single scoring function by
> increasing its reference count). I seem to recall that you were  
> stuck at
> the Python interface. If this is still the case, I can take a look,  
> as I
> (probably) know a bit about the SWIG internals.
>
> If others think reference counting of IMP objects is a bad idea, now's
> the time to say...
>
> 	Ben
> --
>                       http://salilab.org/~ben/
> "It is a capital mistake to theorize before one has data."
> 	- Sir Arthur Conan Doyle
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