shared data

i''m trying to design a number of objects that would take care of problems, which arise when using shared data on multiple threads. and i need help most of these objects will be COM-like. they''ll have reference counting which will in combination with smart pointers take care of automatic cleanup. so, the first object to create is a base which will provide ref counting. since these will be shared data, normal ref counting does not provide everything i want. with the help of a GD community i came up with this: pseudocode

class MTRefCountedObject
{
   public:
       void AddRef    (const ThreadID&);
       void Release   (const ThreadID&);
   protected:
        map<ThreadID, uint>       mdRefMap;
        status_bitset             mdStatus;         
};

so, when using addref and release, we need to provide the "users" thread id. if object is used in nonMT enviroment, only one item is created in the map and the status is having the "notshared" flag. if used by multiple threads, more items are created and the status flag is chaneged to "shared". now, this class provides a base for smart pointer templated class. the next thing is the actuall data wrapper. as i see it, we need accessor functions which work based on the status. if shared flag is set, these functions will use internal locking, if not, "normal" way will be used. pseudocode

template
class SharedData<TYPE>: public MTRefCountedObject
{
    public:
      TYPE  ReadData     ();
            WriteData    (TYPE);
    protected:
    private:
        TYPE         mdData;    // actuall data

};

1) however, one thing is giving me troubles. how should read data be returned? as a temporary? is it logical to assume that "users" have their local copy of that object? what bout writing? 2) one idea is also to make a double buffered SharedData. now, this gives me an idea to make a base class (abstract?) "SharedData", on which SharedDataSimple and SharedDataDoubleBuf would be implemented. this makes any sense? Abnormal behaviour of abnormal brain makes me normal...