sequences containig object references

[Sai-Lai Lo]

Bernd Daum <daum@dik.maschinenbau.tu-darmstadt.de> writes:

> interface List_of_Requirements_OB {
>    void get_Requirements(in string name, out T_list list);
> };
> 
> 
> C++ -code:
> 
> Corba-Client:
>                 .		.
> T_list_var* list = new T_list();
                     ^^^^^^^^^^^^^ 

                     This is not necessary because the second
                     argument is an OUT. The sequence returned by the new
                     operator would be deallocated and overwritten
                     internally by the return value of get_Requirements. 
                     However, this is harmless under omniORB. In other
                     ORBs, for example Orbix, their handling of T_var
                     arguments may not be fully compliant and may result
                     in a memory leak if you assign a sequence to a T_var
                     and then use the T_var as an OUT argument.

> 
> Corba-server: implementation of the server method:
> 
> List_of_Requirements_OB::get_Requirements( const char *  name, T_list *&
> list) {
>                 .
> 		.
>   list = new T_list();
>   list->length(0);
> 
>   for (CORBA::ULong i=0;iter.next()!=0;i++)
>     {
>       Requirement_OB_i *reqobj = new Requirement_OB_i();  //instantiation
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         You have to call reqobj->_obj_is_ready(boa) to finish the
         instantiation of the object implementation. From this point onwards,
         the BOA will manage the object and dispatch calls to it.

>       reqobj->name("temperature");  // populating the object
>       list->length(i+1);
>       (*list)[i] = reqobj;  // inserting in the 'sequence'
        ^^^^^^^^^^^^^^^^^^^^

        Should use (*list)[i] = reqobj->_this(); instead.
          1. It is a bad practice and non-portable to assume that
             an object implementation can be implicitly casted to an
             object reference.
          2. CORBA C++ mapping's memory management rule dictates that
             for an OUT sequence argument, the callee (your server) is 
             responsible for the allocating the storage and the caller
             (your client) is responsible for releasing the storage.
             When the client is remote, the callee is the stub code.
             Hence the storage of the sequence would be freed by the stub
             code when the sequence has been marshalled onto the network
             connection. In this example, a CORBA::release() would be
             called in the stub on each of the element of the sequence.


Regards,
Sai-Lai
-- 
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