linux-kernel - Re: [PATCH v14 1/7] rust: sync: add `OnceLock`

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Message-ID: <CAH5fLggY2Ei14nVJzLBEoR1Rut1GKU4SZX=+14tuRH1aSuQVTA@mail.gmail.com>
Date: Wed, 2 Jul 2025 16:50:30 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Benno Lossin <lossin@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, Trevor Gross <tmgross@...ch.edu>, 
	Adam Bratschi-Kaye <ark.email@...il.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, 
	Daniel Gomez <da.gomez@...sung.com>, Simona Vetter <simona.vetter@...ll.ch>, 
	Greg KH <gregkh@...uxfoundation.org>, Fiona Behrens <me@...enk.dev>, 
	Daniel Almeida <daniel.almeida@...labora.com>, linux-modules@...r.kernel.org
Subject: Re: [PATCH v14 1/7] rust: sync: add `OnceLock`

On Wed, Jul 2, 2025 at 3:54 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> "Alice Ryhl" <aliceryhl@...gle.com> writes:
>
> > On Wed, Jul 2, 2025 at 3:19 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
> >>
> >> Introduce the `OnceLock` type, a container that can only be written once.
> >> The container uses an internal atomic to synchronize writes to the internal
> >> value.
> >>
> >> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> >
> > This type provides no way to wait for initialization to finish if it's
> > ongoing. Do you not need that?
>
> I don't, and in my use case it would cause a deadlock to wait. Anyway,
> it might be useful to others. Would you add it now, or wait for a user?

Waiting would require additional fields so it should probably be a
different type. It's more that we probably want the OnceLock name for
that other type for consistency with stdlib, so perhaps this should be
renamed? The name could be SetOnce or similar.

Alice