Re: memory barriers (was: Yes, WaitLatch is vulnerable to weak-memory-ordering bugs)

On Thu, Sep 22, 2011 at 10:53 AM, Peter Geoghegan <peter(at)2ndquadrant(dot)com> wrote:
> As I've already pointed out, the comment "Won't work on Visual Studio
> 2003" is not accurate:
>
> http://msdn.microsoft.com/en-us/library/f20w0x5e(v=vs.71).aspx
>
> Besides, if it's not supported, why bother mentioning it?

I mentioned it because it took me a long time to figure out whether it
was supported or not, and I finally came to the conclusion that it
wasn't. I stand corrected, though; I've now removed that reference.
Sorry for not jumping on it sooner; it was still vaguely on my list of
things to fix at some point, but it hadn't percolated to the top yet.

The attached version (hopefully) fixes various other things people
have complained about as well, including:

- Heikki's complaint about sometimes writing atomic instead of barrier
(which was leftovers), and
- Gurjeet's complaint that I hadn't defined the variable anywhere

I've also added a lengthy README file to the patch that attempts to
explain how barriers should be used in PostgreSQL coding. It's
certainly not a comprehensive treatment of the topic, but hopefully
it's enough to get people oriented. I've attempted to tailor it a bit
to PostgreSQL conventions, like talking about shared memory vs.
backend-private memory instead of assuming (as a number of other
discussions of this topic do) a thread model. It also includes some
advice about when memory barriers shouldn't be used or won't work, and
some references for further reading.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company