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From: Wedson Almeida Filho <wedsonaf@gmail.com>
To: Josh Stone <jistone@redhat.com>
Cc: "Greg KH" <gregkh@linuxfoundation.org>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Peter Zijlstra" <peterz@infradead.org>,
	rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Will Deacon" <will@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Vincenzo Palazzo" <vincenzopalazzodev@gmail.com>
Subject: Re: [RFC 2/5] rust: sync: Arc: Introduces ArcInner::count()
Date: Fri, 3 Feb 2023 16:22:44 -0300	[thread overview]
Message-ID: <CANeycqo088O+yCA91hujZtxZzbR4UyYrj_yvGYHp0MgWatxmpA@mail.gmail.com> (raw)
In-Reply-To: <9d144ca0-5cf2-a575-a30b-22f5ff4e8e2b@redhat.com>

On Fri, 3 Feb 2023 at 16:17, Josh Stone <jistone@redhat.com> wrote:
>
> On 2/2/23 11:38 PM, Greg KH wrote:
> > How?  Because you have an implicit reference on it already?  If so, then
> > why does reading from it matter at all, as if you have a reference, you
> > know it isn't 0, and that's all that you can really care about.  You
> > don't care about any number other than 0 for a reference count, as by
> > definition, that's what a reference count does :)
>
> There is an additional ability for 1, mentioned up thread -- if you have
> &mut Arc<T>, and the inner count is 1, then you *know* there aren't any
> other Arc<T> handles anywhere else. Then it is safe to return an
> exclusive &mut T, like the upstream Arc::get_mut and Arc::make_mut. This
> can also be used for owned Arc<T> like the upstream Arc::try_unwrap.

The `Arc<T>` in the kernel is pinned so we can't return an `&mut T`,
though a `Pin<&mut T>` would be ok.

  reply	other threads:[~2023-02-03 19:23 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-01 23:22 [RFC 0/5] rust: sync: Arc: Implement Debug and Display Boqun Feng
2023-02-01 23:22 ` [RFC 1/5] rust: sync: impl Display for {Unique,}Arc Boqun Feng
2023-02-02 14:15   ` Gary Guo
2023-02-02 16:50   ` Björn Roy Baron
2023-02-04 10:20   ` Finn Behrens
2023-02-04 18:47   ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 2/5] rust: sync: Arc: Introduces ArcInner::count() Boqun Feng
2023-02-02  9:14   ` Peter Zijlstra
2023-02-02 13:46     ` Boqun Feng
2023-02-02 14:21     ` Gary Guo
2023-02-02 15:41       ` Greg KH
2023-02-02 16:10         ` Boqun Feng
2023-02-02 16:17           ` Greg KH
2023-02-02 16:51             ` Boqun Feng
2023-02-02 21:47               ` Miguel Ojeda
2023-02-03  5:22                 ` Greg KH
2023-02-03  7:25                   ` Boqun Feng
2023-02-03  7:38                     ` Greg KH
2023-02-03  7:43                       ` Boqun Feng
2023-02-03  8:01                       ` Boqun Feng
2023-02-03 19:17                       ` Josh Stone
2023-02-03 19:22                         ` Wedson Almeida Filho [this message]
2023-02-02 14:22   ` Gary Guo
2023-02-04 18:48   ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 3/5] rust: sync: Arc: Introduces Arc::get_inner() helper Boqun Feng
2023-02-02 14:24   ` Gary Guo
2023-02-02 16:53   ` Björn Roy Baron
2023-02-04 18:51   ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 4/5] rust: sync: impl Debug for {Unique,}Arc Boqun Feng
2023-02-02 14:28   ` Gary Guo
2023-02-03 19:46     ` Boqun Feng
2023-02-04 18:56   ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 5/5] sample: rust: print: Add sampe code for Arc printing Boqun Feng
2023-02-02 16:56   ` Björn Roy Baron
2023-02-04 10:22   ` Finn Behrens
2023-02-04 19:05   ` Vincenzo Palazzo

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