[boost] Re: shared_ptr and serialization

From: Russell Hind (rh_gmane_at_[hidden])
Date: 2004-11-20 01:05:27

Robert Ramey wrote:
> 
> the de-serialization of a vector is somethng like:
> 
> template<class Archive, class T>
> void load(Archive ar, vector<T> & v){
>     unsigned int count;
>     ar >> count;
>     v.clear();
>     while(--count){
>         T t;
>         ar >> t;
>         v.push_back(t)
>    }
> }
> 
>>From my reading of the weak_ptr document, a weak_ptr cannot point to
> anything if there is no existent correspnding shared pointer.  So the above
> would necessarily fail unless a shared_ptr was previously serialized in the
> same archive - which is not guarenteed.  In order to use such a data
> structure, the default implementation of the serialization of vector would
> have to be overriden.

 From a users's point of view, how I'd expect/like this to work is that 
if a weak pointer is serialized first, then the actual shared object is 
serialized.  On the way back in (loading) the weak pointer can be read 
and will point to a valid shared object *until* the archive is closed. 
At that point, if the user doesn't have a shared_ptr to the object, then 
the object is deleted but up until then, the weak_ptr is valid.

Yes it is ultimately a user error to serialize *only* a weak pointer, 
but I don't believe it should be a user error to serialize a weak_ptr 
before a shared_ptr.  IMHO, the library should keep the object alive 
(i.e. hold a shared_ptr to any de-serialized pointers, shared or weak) 
until the archive is closed.

But I haven't really looked at the implementation of shared_ptr and 
serialization, so this is just how I'd 'expect' it to work

Cheers

Russell