linux-kernel - Re: [PATCH 12/13] rust: sync: introduce `CondVar`

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Message-ID: <ZCWgKnuRpUfWs2wT@wedsonaf-dev>
Date:   Thu, 30 Mar 2023 11:43:54 -0300
From:   Wedson Almeida Filho <wedsonaf@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rust-for-linux@...r.kernel.org, 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>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <walmeida@...rosoft.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 12/13] rust: sync: introduce `CondVar`

On Thu, Mar 30, 2023 at 02:52:23PM +0200, Peter Zijlstra wrote:
> On Thu, Mar 30, 2023 at 01:39:53AM -0300, Wedson Almeida Filho wrote:
> > From: Wedson Almeida Filho <walmeida@...rosoft.com>
> > 
> > This is the traditional condition variable or monitor synchronisation
> > primitive. It is implemented with C's `wait_queue_head_t`.
> > 
> > It allows users to release a lock and go to sleep while guaranteeing
> > that notifications won't be missed. This is achieved by enqueuing a wait
> > entry before releasing the lock.
> > 
> 
> > +/// A conditional variable.
> > +///
> > +/// Exposes the kernel's [`struct wait_queue_head`] as a condition variable. It allows the caller to
> > +/// atomically release the given lock and go to sleep. It reacquires the lock when it wakes up. And
> > +/// it wakes up when notified by another thread (via [`CondVar::notify_one`] or
> > +/// [`CondVar::notify_all`]) or because the thread received a signal. It may also wake up
> > +/// spuriously.
> 
> Urgh so wide :-/

Thanks for reviewing :)

> But no, threads can *always* and for any reason, have spurious wakeups.

I don't believe I said otherwise. Is there anything in the text above you'd like to see changed?

> Also, is this hard tied to mutex? If so, you should probably use swait
> instead of wait.

This is not tied to mutex, it works with any lock.

Cheers,
-Wedson