From: David Abrahams (dave_at_[hidden])
Date: 2008-08-16 05:37:53
on Sat Aug 16 2008, "Eduardo Panisset" <eduardo.panisset-AT-gmail.com> wrote:
> Excuse me for insisting on my question,
>
> But I would like to ensure that I'm understanding shared_ptr correctly.
Okay, but please use standard quoting so threading is preserved:
> > Not without additional synchronization (e.g. via a mutex with all
> > threads cooperating by locking before accessing the shared_ptr). But do
> > you really need to do that? Can you not give each thread that needs
> > access a separate copy of the shared_ptr?
>
> Exactly. I give each thread a instance of shared_ptr, but the point is: the
> critical region of release member function does not avoid race conditions
> because It does not protect de code right below:
>
> if( new_use_count == 0 )
> {
> dispose();
> weak_release();
> }
>
> How Can I ensure that the release member function wouldn't dispose a pointee
> more than one time ? (release executing concurrently from different
> shared_ptr instances)
Because the reference count was 1, there can be only one shared_ptr
instance that owns the pointee. No other threads can be referencing it.
[In fact it's very likely that no mutex is used on any given platform --
atomic reference counting is used where available.]
-- Dave Abrahams BoostPro Computing http://www.boostpro.com