Re: [Boost-bugs] [Boost C++ Libraries] #9601: Unable to load archives with pointer instances which contain self reference cycles in 1.55

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #9601: Unable to load archives with pointer instances which contain self reference cycles in 1.55
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-01-22 20:12:14

#9601: Unable to load archives with pointer instances which contain self reference
cycles in 1.55
-------------------------------+---------------------------
  Reporter:  brandon.kohn      |      Owner:  ramey
      Type:  Bugs              |     Status:  assigned
 Milestone:  To Be Determined  |  Component:  serialization
   Version:  Boost 1.55.0      |   Severity:  Problem
Resolution:                    |   Keywords:
-------------------------------+---------------------------

Comment (by brandon.kohn):

 Replying to [comment:1 ramey]:
 > boy - I bet this cost  a lot of effort to figure out.
 Yeah, it's fun stuff :). Anyone who doesn't appreciate the intricacies of
 implementing a serialization library needs to spend time debugging one.

 >
 > Note that the test set includes a specific test for cyclic pointers
 which is passing.
 >
 > I'm thinking that the difference between that test and your test isn't
 so much a cycle as a self referential object.
 If you mean serialization\test\test_cyclic_ptrs.cpp, I'll give it a more
 thorough look.

 We've been using boost serialization at my work for our application files
 and have just recently moved from 1.53 to 1.55 to support vc12. The use
 case where I found this was more complex than the unit-test as it involved
 polymorphic types held in shared_ptr instances with the cyclic reference
 being held inside a std::map member variable. The unit-test was just the
 most simple cycle I could think of which illustrated the issue.

 > I'm also thinking that the correct fix is to tweak the code so that it
 addresses the special case of a self referential object such as yours.
 > *snip*
 > This is predicated on my guess that this is really just a corner case I
 failed to consider and not some fundamental issue which requires a major
 overhaul.  If I'm wrong about this, feel free to let me know.
 >
 My suspicion is that it would affect any cycle, but I've been wrong before
 ;). I'm already having a think about how I would fix it.

 One note is that it worked in 1.53. It seems to have stopped working when
 a change was made to :
 {{{
 #!c++
 // remember that that the address of these elements could change
 // when we make another call so don't use the address
 bpis_ptr->load_object_ptr(
   ar,
   t,//! used to be object_id_vector[ui].address
   m_pending.version
 );
 }}}
 And then in iserializer.hpp (the old version before SHA:
 8af0e20bb091631a153147587d7958492be623ae):
 {{{
 #!c++
 BOOST_DLLEXPORT void pointer_iserializer<Archive, T>::load_object_ptr(
     basic_iarchive & ar,
     void * & x,
     const unsigned int file_version
 ) const
 {
     Archive & ar_impl =
         boost::serialization::smart_cast_reference<Archive &>(ar);

     auto_ptr_with_deleter< T > ap(heap_allocator< T >::invoke());
     if(NULL == ap.get())
         boost::serialization::throw_exception(std::bad_alloc()) ;

     T * t = ap.get();
     x = t;//! This would update the object_id_vector[ui].address member
 with the right ptr.
 }}}

 The new code doesn't do this. So my first idea for a fix would be to
 create a version of load_object_ptr with an overload to update the address
 member of that vector as before.

 There is a comment:
 {{{
 #!c++
 // remember that that the address of these elements could change
 // when we make another call so don't use the address
 }}}

 It makes me wonder if there's something funky that can happen to that
 address which I might be missing.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9601#comment:2>
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