Re: Promoting weak pointers

On Jun 11, 6:10 pm, Michiel Helvensteijn <m.helvenste...@gmail.com>
wrote:
> So the main question would be: Can anyone think of a use-case for
> promotion of a weak pointer in which there is no obvious alternative?


One reason you may want to promote a weak reference to a strong
reference is under contention from different thread contexts. In fact
where there is contention, the system should *require* promotion
before dereferencing.


Consider:


      if (my_weak_ptr != NULL)
                my_weak_ptr->do_something();


Here if my_weak_ptr's target is garbage collected in another thread
between the test and when it is used than you are going to dereference
null.


Better to:


        my_strong_ptr = my_weak_ptr;
        if (my_strong_ptr != NULL)
                my_strong_ptr->do_something();


That way the strong reference will provide protection for the critical
section of code.


Enjoy,
Andrew.
--
Andrew Tomazos <andrew@tomazos.com> <http://www.tomazos.com>
[In every system I've seen with strong and weak pointers, the pointer
values are all either filled in or not before the program starts. I
suppose there might be race conditions if you do dynamic linking, but
that's a separate issue. -John]

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