Re: [Boost-users] [Boost.serialization] unexpected bad_cast exception while deserializing some arbitrary instances (e.g.: ar & data) ...

Subject: Re: [Boost-users] [Boost.serialization] unexpected bad_cast exception while deserializing some arbitrary instances (e.g.: ar & data) ...
From: Robert Ramey (ramey_at_[hidden])
Date: 2009-05-26 14:21:07

I think this is a manifestation of bug reported with the 1.39 version of the 
library.
I'm trying to fix this but so far I haven't been able to
implement a satisfactory solution.  stay tuned.

Robert Ramey

Francois Mauger wrote:
> Hi serializers!
>
> Let me present my problem:
>
> I have a class, named 'io_factory', that enables to deserialize
> an arbitrary object from a text (or XML) archive using the
> following '__load_text' template method:
>
> -8<---------------------------------------------------------------------
>
>      class io_factory
>      {
>        ...
>
>        template <typename Data>
>        void __load_text (boost::archive::text_iarchive & ar_,
> Data & data_)
>        {
> Data & b = data_;
> std::cerr << "DEVEL: io_factory::__load_text: archive class name='"
>   << typeid (ar_).name () << "'"
>   << std::endl;
> std::cerr << "DEVEL: io_factory::__load_text: class name='"
>   << typeid (b).name () << "'"
>   << std::endl;
> try
>   {
>     /* Here I may experience an unexpected exception
>               * only in very special circumstances:
>               */
>     ar_ >> b;
>     std::cerr << "DEVEL: io_factory::__load_text: deserialization is
>       ok." << std::endl;
>   }
> catch (std::exception & x)
>   {
>     std::cerr << "DEVEL: io_factory::__load_text: EXCEPTION="
>       << x.what ()
>       << std::endl;
>
>   }
> std::cerr << "DEVEL: io_factory::__load_text: done"
>   << std::endl;
>        }
>        ...
>     };
>
> -8<---------------------------------------------------------------------
>
> I wrote a shared library that makes use of this template code segment.
> Using a test program, as I try to deserialize an instance of
> some 'nemo3::ana_event' class from a Boost text archive file,
> it prints:
>
> -8<---------------------------------------------------------------------
> DEVEL: io_factory::__load_text: archive class
> name='N5boost7archive13text_iarchi
> veE'
> DEVEL: io_factory::__load_text: class name='N5nemo39ana_eventE' <= ok
> 'nemo3::ana_event'
> DEVEL: io_factory::__load_text: deserialization is ok.  <==== IT
> WORKS! DEVEL: io_factory::__load_text: done
> -8<---------------------------------------------------------------------
>
> This is fine! My object is properly loaded from the file.
> My test program works as expected.
>
> Well, now, I also have a Python module that wraps some C++ code
> and the 'io_factory' class. I use Boost.Python to do that.
>
> When I run my Python program, importing this wrapper module, to
> deserialize the same Boost text archive file from the python shell; it
> prints:
>
> -8<---------------------------------------------------------------------
> ...
> DEVEL: io_factory::__load_text: archive class
> name='N5boost7archive13text_iarchiveE'
> DEVEL: io_factory::__load_text: class name='N5nemo39ana_eventE'
> DEVEL: io_factory::__load_text: EXCEPTION=std::bad_cast  <= OOOOPS!
> DEVEL: io_factory::__load_text: done
> ...
> -8<---------------------------------------------------------------------
>
> As you can see, there is a nasty 'std::bad_cast' thrown exception from
> the "ar_ >> b;" statement. This code works perfectly in the first
> case, now something is broken and I cannot figure out what!
>
> I am really confused by this issue. I already used
> exactly the same approach within another library (also based on
> Boost.serialization and Boost.Python) and I never met any problem.
> More, I also have a smaller python script that uses the same
> wrapper module with the same input archive file and it works:
> I can read all the instances I stored in my archive file!
> If I use an XML archive, the problem is exactly the same: it works in
> the first case, not in the last one.
>
> I do not understand where this 'bad_cast' exception comes from.
> For me it as nothing to do with:
> - the format of the archive (I know the archive file is ok as the test
> program store/load is properly)
> - the wrapping within Python (I can make it run ok within a sample
> python script)
>
> I really need a hint that could help me to understand this issue.
> It seems this problem looks like a side-effect (?)
> anyway the deep reason is outside of the scope of my code and my
> knowledge.
> My config is:
>
> * OS:
>    Ubuntu Linux 8.04
>
> * Linux Kernel:
>    $ uname -a
>    Linux mauger-laptop 2.6.24-24-generic #1 SMP Wed Apr 15 15:54:25
> UTC 2009 i686 GNU/Linux
>
> * Boost:
>    $ boost-config --version
>    1_38_0
>
> * gcc:
>    $ g++ --version
>    g++ (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu3)
>
> * Python 2.5
>
> I'd really appreciate your comments.
> I'm afraid I cannot send a small sample code that could reproduce
> this 'bug' in a simpler way as it comes only at a quite high level on
> top of 3 big shared libraries + Boost + Python.
> My attempt to isolate some critical code to see this side-effect
> within "Boost.serialization only" or "Boost.Python only" failed.
> More it confirms that the code works as expected (hum... or seems to
> work...).
>
> Thanks a lot for your help.
>
> regards
>
> frc