Re: Additional Glib::RefPtr Safety Mechanism

On Thu, 29 Aug 2019 at 21:27, Karsten Pedersen <[email protected]> wrote:

> Hi all,
>
> One area of C++ that always frustrates me is safety. Smart pointers
> such as the Glib::RefPtr go a good way to avoid dangling pointers, use
> after free, etc. However one area where this (and std::shared_ptr) is
> lacking is that it is very easy for "this" to dangle and there really
> is no protection against it. Check out a very simple example here:
>
> https://github.com/osen/sr1/blob/master/src/tests/dangling_this.cpp
>
>
Is this actually a common problem that needs to be solved?

It seems like a solution in search of a problem. IMO you should just avoid
using globals like this when possible, and use them carefully when
necessary.

For the shared_ptr example, you can solve the problem simply by copying the
global into a local variable in the one function that needs to do it. That
way you don't pay the cost in every function that uses operator->

  void broken()
  {
    auto keepalive = d;
    d = std::sr1::shared_ptr<Dummy>();
    dummy = 9;
  }

That keeps *this alive until the end of the function.

Or slightly more efficiently:

  void broken()
  {
    auto keepalive = std::move(d);
    d = std::sr1::shared_ptr<Dummy>();
    dummy = 9;
  }

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