[boost] Re: Serialization - Ref-counting

From: Dave Harris (brangdon_at_[hidden])
Date: 2002-11-17 11:28:34

In-Reply-To: <01C28DC2.8F345AA0_at_[hidden]>
Are reference-counted objects supported? If I am using my own 
reference-counted class, what do I have to do to get serialisation to work 
for it?

To clarify: obviously the archive needs some kind of table of loaded 
objects, so that it can ensure two references to the same object still 
refer to the same object when loaded. If the objects are 
reference-counted, this table needs to understand the kind of 
reference-counting used. It needs an appropriate kind of smart pointer. Is 
this supported? If so, how?

I have looked at the posted code but I've not been able to figure it all 
out. I see lots of use of (T *), which is wrong.

I ask because in the past I have been bitten by Microsoft's MFC system, 
which makes no provision for reference counting. The problem code was 
something like:

    MyItem heres_one_I_prepared_earlier;
    smart_ptr<MyItem> p1, p2;
    
    ar >> p1;
    if (*p1 == heres_one_I_prepared_earlier)
        p1 = &heres_one_I_prepared_earlier;
        
    ar >> p2;  // Bang.
    if (*p2 == heres_one_I_prepared_earlier)
        p2 = &heres_one_I_prepared_earlier;
        
The assignment to p1 decrements the loaded object's ref-count. If p1 and 
p2 refered to the same object when they were stored, and the archive 
hasn't incremented the ref-count, then the object will have been deleted 
before p2 gets it.

-- Dave Harris