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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Wed, 2 Jun 2021 10:22:15 +0100
Message-ID: <CAH6eHdQ3Yp84RFSmsDctS+5_BpsYGmPP5j-NqPjB1caksPzCaw@mail.gmail.com>
Subject: Re: std::atomic_shared_ptr
To: Mikhail Matrosov <mikhail.matrosov@gmail.com>
Cc: Thomas Rodgers <rodgert@appliantology.com>,
 "libstdc++" <libstdc++@gcc.gnu.org>
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On Wed, 2 Jun 2021 at 08:10, Mikhail Matrosov via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Hi, Thomas,
>
> > It didn't make the cutoff for GCC11 stage1, I hope to get it into GCC12.
>
> Glad to hear that!
>
> > Also, to set expectations, it will not be a lock free atomic.
>
> Hm. That's surprising. And honestly does not look very useful. We can
> always wrap a shared_ptr in a mutex.

Which is why some people think the feature should never have been
added to the standard in the first place.

> There exist lock-free implementations in the wild. E.g. in folly. Would it
> be possible to adopt one of those?

Probably not, because it would require ABI-breaking changes to
std::shared_ptr, which is out of the question.