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Re: [Qemu-devel] Java volatile vs. C11 seq_cst (was Re: [PATCH v2 1/2] a

From: Paul E. McKenney
Subject: Re: [Qemu-devel] Java volatile vs. C11 seq_cst (was Re: [PATCH v2 1/2] add a header file for atomic operations)
Date: Tue, 18 Jun 2013 18:53:07 -0700
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Jun 18, 2013 at 05:37:42PM +0200, Torvald Riegel wrote:
> On Tue, 2013-06-18 at 07:50 -0700, Paul E. McKenney wrote:
> > First, I am not a fan of SC, mostly because there don't seem to be many
> > (any?) production-quality algorithms that need SC.  But if you really
> > want to take a parallel-programming trip back to the 1980s, let's go!  ;-)
> Dekker-style mutual exclusion is useful for things like read-mostly
> multiple-reader single-writer locks, or similar "asymmetric" cases of
> synchronization.  SC fences are needed for this.

They definitely need Power hwsync rather than lwsync, but they need
fewer fences than would be emitted by slavishly following either of the
SC recipes for Power.  (Another example needing store-to-load ordering
is hazard pointers.)

> > PS:  Nevertheless, I personally prefer the C++ formulation, but that is
> >      only because I stand with one foot in theory and the other in
> >      practice.  If I were a pure practitioner, I would probably strongly
> >      prefer the Java formulation.
> That's because you're a practitioner with experience :)

I knew I had all this grey hair for some reason or another...  ;-)

                                                        Thanx, Paul

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