Re: [boost] storing intrusive_ptr in atomic?!

Subject: Re: [boost] storing intrusive_ptr in atomic?!
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2013-10-25 09:07:36

2013/10/25 Andrey Semashev <andrey.semashev_at_[hidden]>

>  > T * expected1 = 0;
> > T * expected2 = 0;
> > if ( ! a[index].compare_exchange_strong( expected1, expected2) ) {
> >   // expected1 is not NULL, expected1 removed == a[index] contains NULL
> > }
>
> No, that's not right. If compare_exchange_strong returns false, the
> operation
> have failed and a[index] != NULL (at least, that's how
> compare_exchange_strong
> have left it). It should be:
>
> T* expected = a[index].load(memory_order_acquire);
> while (!a[index].compare_exchange_weak(expected, NULL,
> memory_order_release,
> memory_order_acquire))
> {
> }
>
> if (expected)
>   // The expected value was removed from the array
> else
>   // The array element was removed by some other thread
>

agreed - but shouldn't we use strong memory-order
(I remember that Herb S. recommended to use memory_order_strong in one of
its sessions)