linux-kernel - Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator

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Message-ID: <CAH5fLggfMNcuu0KD13_K49NBXXWD133BB6uc5ph7xQi0WTxBZg@mail.gmail.com>
Date: Mon, 3 Jun 2024 19:52:36 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Matt Gilbride <mattgilbride@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, 
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joel@...lfernandes.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Christian Brauner <brauner@...nel.org>, Rob Landley <rob@...dley.net>, 
	Davidlohr Bueso <dave@...olabs.net>, Michel Lespinasse <michel@...pinasse.org>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator

On Mon, Jun 3, 2024 at 7:42 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Mon, Jun 03, 2024 at 04:05:19PM +0000, Matt Gilbride wrote:
> [...]
> > +/// A mutable iterator over the nodes of a [`RBTree`].
> > +///
> > +/// Instances are created by calling [`RBTree::iter_mut`].
> > +pub struct IterMut<'a, K, V> {
> > +    _tree: PhantomData<&'a mut RBTree<K, V>>,
> > +    iter_raw: IterRaw<K, V>,
> > +}
> > +
> > +// SAFETY: The [`RBTreeIterator`] gives out mutable references to K and V, so it has the same
>
> s/RBTreeIterator/IterMut ?
>
> Also `IterMut` doesn't give out mutable references to K, which makes
> me think...
>
> > +// thread safety requirements as mutable references.
> > +unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
> > +
>
> we can lose the constrains to `K: Sync`, right?

Either Send or Sync would be valid here, but almost all types that are
Sync are also Send, but the opposite is not the case. So I wouldn't
consider that to be loosening the constrain.

Alice