Re: [Boost-users] [serialization] dynamically allocatedobjects andreset_object_address

Subject: Re: [Boost-users] [serialization] dynamically allocatedobjects andreset_object_address
From: Robert Ramey (ramey_at_[hidden])
Date: 2008-11-19 15:35:12

joaquin_at_[hidden] wrote:
> Robert Ramey escribió:
>> I'm aware that some problems occur when loading a map of objects
>> containing other objects whose types are tracked
>> or something like that.  I forget the details.  The problem is that
>> when an object is moved and that object contains other objects which
>> are pointed to by other objects,  I'm speaking from memory but may
>> one can get the idea ffrom that.
>>
>> I think we're talking about the same thing.
>
> I am not entirely sure... Let me restate the issue just to be
> confident I'm getting it through.
> Consider this pseudocode:
>
>   T t;
>   ar>>t;
>   v.push_back(t); // copy t somewhere else
>   ar.reset_object_adress(&v.back(),&t); // and communicate it's been
> relocated
>
> This works fine and subsequents pointers to t, when loaded, will point
> to the
> its new location inside v. Now consider the variation:
>
>   T* p;
>   ar>>p; // *p is created and loaded automatically by
>   Boost.Serialization v.push_back(*p); // copy *p somewhere else
>   ar.reset_object_adress(&v.back(),p); // and communicate it's been
> relocated
>
> This does not seem to work: objects created automatically by
> Boost.Serialization when
> loaded through a pointer cannot be relocated with
> reset_object_address: subsequent
> pointers to this object will point to the same object as p, not to the
> element in v.
>
> Having a look at the source code of Boost.Serialization
> (basic_iarchive.cpp) it's
> apparent that moveable_objects_recent and moveable_objects_end are
> updated inside basic_iarchive::load_object, but are not inside
> basic_iarchive::load_pointer.
> Of course, I don't know what the hidden implications of updating these
> also in
> load_pointer could be, but I'd appreciate if you could comment on
> this.

OK, I looked into this.

The list of tracked object that might be relocated as soon is the
library is "done" with them.

line # 392 moveable_objects_recent = this_id;

That is when the stack is shortened.
This keeps the list prety short. I would have to think about this some
more.

>   T* p;
>   ar>>p; // *p is created and loaded automatically by
>   Boost.Serialization v.push_back(*p); // copy *p somewhere else
>   ar.reset_object_adress(&v.back(),p); // and communicate it's been
> relocated

I presume that in your case something like the following wouldn't help?

v.push_back(T());
ar >> v.back(); // assuming v.back() returns a reference

Robert Ramey