Re: Safe to use stdatomic.h?

From: Jeff King <peff@peff.net>
Date: Mar 20, 2017, 20:27 UTC
Message-ID: <20170320202755.ospj7o6dfczti6wp@sigill.intra.peff.net>
In-Reply-To: <000801d2a1b7$1ec41620$5c4c4260$@gmail.com>

On Mon, Mar 20, 2017 at 04:18:20PM -0400, Ben Peart wrote:

Show 10 quoted lines

> My college Jeff is working on a patch series to further parallelize the
> loading of the index.  As part of that patch, it would be nice to use the
> atomic_fetch_add function as that would be more efficient than creating a
> mutex simply to protect a variable so that it can be incremented.  I haven't
> seen any use of atomics yet in Git, nor anything that includes
> <stdatomic.h>.
> 
> GCC has supported them since 4.9 and Clang has supported them by default
> since 3.3.  Are there any compilers currently in use by Git that don't
> support these C11 functions?

Yes, there definitely are older compilers in use. However, if you can abstract the operation you want to perform into its own function, it's perfectly fine to #ifdef it to use the atomics when available and fall back to a mutex otherwise.

-Peff