Date: Thu, 26 Jun 2014 13:21:48 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>,
 Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@heroku.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>, Ants Aasma <ants@cybertec.at>
Subject: Re: better atomics - v0.5
Message-ID: <20140626112148.GC1926@awork2.anarazel.de>
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On 2014-06-25 20:22:31 -0400, Robert Haas wrote:
> On Wed, Jun 25, 2014 at 5:42 PM, Heikki Linnakangas
> <hlinnakangas@vmware.com> wrote:
> > I think having a separate file for each architecture is nice. I totally
> > agree that they don't belong in src/include/storage, though. s_lock.h has
> > always been misplaced there, but we've let it be for historical reasons, but
> > now that we're adding a dozen new files, it's time to move them out.
> 
> I find the current organization pretty confusing, but maybe that could
> be solved by better documentation of what's supposed to go in each
> architecture or compiler-dependent file.

The idea is that first a architecture specific file (atomics-arch-*.h)
is included. That file can provide a (partial) implementation for the
specific architecture. Or it can do pretty much nothing.

After that a compiler specific file is included
(atomics-generic-*.h). If atomics aren't yet implemented that can
provide an intrinsics based implementation if the compiler version has
support for it. At the very least a compiler barrier should be provided.

After that the spinlock based fallback implementation
(atomics-fallback.h) provides atomics and barriers if not yet
available. By here we're sure that nothing else will provide them.

Then we can provide operations (atomics-generic.h) that build ontop of
the provided functions. E.g. implement _sub, _and et al.

I'll include some more of that explanation in the header.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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